Extends JTransforms to reduce memory allocation on a per FFT iteration.

Co-authored-by: denny <dennis.sheirer@gmail.com>

src/main/java/io/github/dsheirer/audio/AbstractAudioModule.java

@@ -35,7 +35,7 @@ import org.slf4j.LoggerFactory;
 public abstract class AbstractAudioModule extends Module implements IAudioSegmentProvider, IdentifierUpdateListener
 {
     private final static Logger mLog = LoggerFactory.getLogger(AbstractAudioModule.class);
-    public static final long DEFAULT_SEGMENT_AUDIO_SAMPLE_LENGTH = 60 * 8000; // 1 minute @ 8kHz
+    public static final long DEFAULT_MAX_SEGMENT_LENGTH_MILLIS = 60_000; // 1 minute
     public static final int DEFAULT_TIMESLOT = 0;
     private final int mMaxSegmentAudioSampleLength;
     private Listener<AudioSegment> mAudioSegmentListener;
@@ -51,12 +51,12 @@ public abstract class AbstractAudioModule extends Module implements IAudioSegmen
      * Constructs an abstract audio module
      *
      * @param aliasList for aliasing identifiers
-     * @param maxSegmentAudioSampleLength in milliseconds
+     * @param maxSegmentLengthMillis maximum audio segment length in milliseconds
      */
-    public AbstractAudioModule(AliasList aliasList, int timeslot, long maxSegmentAudioSampleLength)
+    public AbstractAudioModule(AliasList aliasList, int timeslot, long maxSegmentLengthMillis)
     {
         mAliasList = aliasList;
-        mMaxSegmentAudioSampleLength = (int)(maxSegmentAudioSampleLength * 8); //Convert milliseconds to samples
+        mMaxSegmentAudioSampleLength = (int)(maxSegmentLengthMillis * 8); //Convert milliseconds to samples
         mTimeslot = timeslot;
         mIdentifierCollection = new MutableIdentifierCollection(getTimeslot());
         mIdentifierUpdateNotificationBroadcaster.addListener(mIdentifierCollection);
@@ -67,7 +67,7 @@ public abstract class AbstractAudioModule extends Module implements IAudioSegmen
      */
     public AbstractAudioModule(AliasList aliasList)
     {
-        this(aliasList, DEFAULT_TIMESLOT, DEFAULT_SEGMENT_AUDIO_SAMPLE_LENGTH);
+        this(aliasList, DEFAULT_TIMESLOT, DEFAULT_MAX_SEGMENT_LENGTH_MILLIS);
     }
 
     /**

src/main/java/io/github/dsheirer/audio/codec/mbe/JmbeAudioModule.java

@@ -59,7 +59,7 @@ public abstract class JmbeAudioModule extends AbstractAudioModule implements Lis
 
     public JmbeAudioModule(UserPreferences userPreferences, AliasList aliasList, int timeslot)
     {
-        super(aliasList, timeslot, DEFAULT_SEGMENT_AUDIO_SAMPLE_LENGTH);
+        super(aliasList, timeslot, DEFAULT_MAX_SEGMENT_LENGTH_MILLIS);
         mUserPreferences = userPreferences;
         MyEventBus.getGlobalEventBus().register(this);
         loadConverter();

src/main/java/io/github/dsheirer/audio/playback/AudioChannel.java

@@ -46,6 +46,12 @@ public class AudioChannel implements Listener<IdentifierUpdateNotification>
      * sample rate.
      */
     public static final int SAMPLES_PER_INTERVAL = 160;
+    /**
+     * Quantity of consecutive intervals without new audio (1 second) before an incomplete audio segment is treated as
+     * stalled and abandoned.  An audio segment is delivered once to a single channel, so abandoning a segment that is
+     * still live loses the rest of the call.  This has to tolerate decoder gaps, such as a missed P25 LDU (180 ms).
+     */
+    static final int MAX_STALLED_INTERVALS = 50;
     private static final Logger LOGGER = LoggerFactory.getLogger(AudioChannel.class);
     private final AudioBuffer mAudioBuffer = new AudioBuffer();
     private final Broadcaster<AudioEvent> mAudioEventBroadcaster = new Broadcaster<>();
@@ -225,7 +231,7 @@ public class AudioChannel implements Listener<IdentifierUpdateNotification>
         }
 
         //Dispose completed/fully-played audio segments and segments that have stalled/failed to progress
-        if(mCurrentAudioSegment != null && ((mNoAudioFromSegmentIntervalCount >= 6) ||
+        if(mCurrentAudioSegment != null && ((mNoAudioFromSegmentIntervalCount >= MAX_STALLED_INTERVALS) ||
           (mCurrentAudioSegment.isComplete() && (mCurrentBufferIndex >= mCurrentAudioSegment.getAudioBufferCount()))))
         {
             disposeCurrentAudioSegment();
@@ -401,6 +407,24 @@ public class AudioChannel implements Listener<IdentifierUpdateNotification>
         return mAudioSegmentQueue.isEmpty();
     }
 
+    /**
+     * Next audio segment queued for playback, without removing it from the queue.
+     * @return queued audio segment or null if the queue is empty.
+     */
+    AudioSegment peekQueuedAudioSegment()
+    {
+        return mAudioSegmentQueue.peek();
+    }
+
+    /**
+     * Removes the next audio segment from the queue, transferring it (and its consumer count) to the caller.
+     * @return queued audio segment or null if the queue is empty.
+     */
+    AudioSegment pollQueuedAudioSegment()
+    {
+        return mAudioSegmentQueue.poll();
+    }
+
     /**
      * Schedules the audio segment for playback.  The audio segment user count should already be incremented by the
      * calling entity.
@@ -475,6 +499,7 @@ public class AudioChannel implements Listener<IdentifierUpdateNotification>
         }
 
         mCurrentBufferIndex = -1;
+        mNoAudioFromSegmentIntervalCount = 0;
     }
 
     /**

src/main/java/io/github/dsheirer/audio/playback/AudioPlaybackManager.java

@@ -173,6 +173,7 @@ public class AudioPlaybackManager implements Listener<AudioSegment>, IAudioContr
         {
             Iterator<AudioSegment> it = mAudioSegments.iterator();
             AudioSegment audioSegment;
+            List<AudioSegment> displaced = new ArrayList<>();
 
             //Remove any audio segments flagged as do not monitor.  Don't remove completed segments yet, because
             //we want to give them a brief chance at playback.  Automatically assign linked audio segments to the
@@ -200,6 +201,16 @@ public class AudioPlaybackManager implements Listener<AudioSegment>, IAudioContr
                                 if(audioOutput.isLinkedTo(audioSegment))
                                 {
                                     it.remove();
+
+                                    //Linked audio continues the current call, so it goes ahead of anything queued
+                                    AudioSegment queued = audioOutput.pollQueuedAudioSegment();
+
+                                    while(queued != null)
+                                    {
+                                        displaced.add(queued);
+                                        queued = audioOutput.pollQueuedAudioSegment();
+                                    }
+
                                     audioOutput.play(audioSegment);
                                 }
                             }
@@ -212,6 +223,8 @@ public class AudioPlaybackManager implements Listener<AudioSegment>, IAudioContr
                 }
             }
 
+            mAudioSegments.addAll(displaced);
+
             //Sort audio segments by playback priority and assign to empty audio outputs
             if(!mAudioSegments.isEmpty() && mAudioOutput != null)
             {
@@ -232,6 +245,8 @@ public class AudioPlaybackManager implements Listener<AudioSegment>, IAudioContr
                             }
                         }
                     }
+
+                    replaceLowerPriorityQueuedSegments(mAudioSegments, mAudioOutput.getAudioProvider().getAudioChannels());
                 }
                 finally
                 {
@@ -255,6 +270,40 @@ public class AudioPlaybackManager implements Listener<AudioSegment>, IAudioContr
         }
     }
 
+    /**
+     * Swaps audio segments queued on the audio channels for waiting audio segments that have a higher playback priority,
+     * so that a segment queued behind the current playback can't hold a higher priority segment out of the channel.
+     * Audio that is currently playing is not interrupted.  Displaced segments are returned to the waiting list.
+     *
+     * @param waiting audio segments, sorted by playback priority.
+     * @param audioChannels to evaluate.
+     */
+    static void replaceLowerPriorityQueuedSegments(List<AudioSegment> waiting, List<AudioChannel> audioChannels)
+    {
+        for(AudioChannel audioChannel: audioChannels)
+        {
+            if(waiting.isEmpty())
+            {
+                return;
+            }
+
+            AudioSegment queued = audioChannel.peekQueuedAudioSegment();
+
+            if(queued != null &&
+               waiting.getFirst().monitorPriorityProperty().get() < queued.monitorPriorityProperty().get())
+            {
+                //The audio thread may have taken the queued segment since the peek, so only return what we removed.
+                queued = audioChannel.pollQueuedAudioSegment();
+                audioChannel.play(waiting.removeFirst());
+
+                if(queued != null)
+                {
+                    waiting.add(queued);
+                }
+            }
+        }
+    }
+
     public void dispose()
     {
         MyEventBus.getGlobalEventBus().unregister(this);

src/main/java/io/github/dsheirer/audio/playback/AudioProvider.java

@@ -30,6 +30,16 @@ import javax.sound.sampled.AudioFormat;
  */
 public abstract class AudioProvider
 {
+    /**
+     * Converts the audio sample to a 16-bit PCM sample, limiting out of range values instead of allowing them to wrap.
+     * @param sample in range -1.0 to 1.0
+     * @return PCM sample
+     */
+    protected static short toPcm(float sample)
+    {
+        return (short)(Math.clamp(sample, -1.0f, 1.0f) * Short.MAX_VALUE);
+    }
+
     /**
      * Audio format for this provider
      */

src/main/java/io/github/dsheirer/audio/playback/AudioProviderMono.java

@@ -77,7 +77,7 @@ public class AudioProviderMono extends AudioProvider
 
         for(int x = 0; x < AudioChannel.SAMPLES_PER_INTERVAL; x++)
         {
-            shortBuffer.put((short) (audio[x] * Short.MAX_VALUE));
+            shortBuffer.put(toPcm(audio[x]));
         }
 
         return buffer;

src/main/java/io/github/dsheirer/audio/playback/AudioProviderMultiChannel.java

@@ -108,7 +108,7 @@ public class AudioProviderMultiChannel extends AudioProvider
         {
             for(int channelNumber = 0; channelNumber < mAudioChannels.size(); channelNumber++)
             {
-                shortBuffer.put((short)(samples[channelNumber][sampleCounter] * Short.MAX_VALUE));
+                shortBuffer.put(toPcm(samples[channelNumber][sampleCounter]));
             }
         }
 

src/main/java/io/github/dsheirer/audio/playback/AudioProviderStereo.java

@@ -102,8 +102,8 @@ public class AudioProviderStereo extends AudioProvider
 
         for(int x = 0; x < AudioChannel.SAMPLES_PER_INTERVAL; x++)
         {
-            shortBuffer.put((short)(left[x] * Short.MAX_VALUE));
-            shortBuffer.put((short)(right[x] * Short.MAX_VALUE));
+            shortBuffer.put(toPcm(left[x]));
+            shortBuffer.put(toPcm(right[x]));
         }
 
         return buffer;

src/main/java/io/github/dsheirer/dsp/am/AmAudioNormalizer.java

@@ -0,0 +1,117 @@
+/*
+ * *****************************************************************************
+ * Copyright (C) 2014-2026 Dennis Sheirer
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program.  If not, see <http://www.gnu.org/licenses/>
+ * ****************************************************************************
+ */
+package io.github.dsheirer.dsp.am;
+
+/**
+ * Converts an AM envelope to audio by removing the carrier (DC) and scaling the audio by the carrier level.
+ *
+ * An AM signal's envelope is carrier * (1 + modulation), so using the carrier as the gain reference gives audio that
+ * follows the modulation depth of the transmission, independent of the received signal strength and without the
+ * pumping of an audio peak based AGC.
+ *
+ * The carrier estimate uses a cumulative mean at the start of a transmission to lock quickly and without a transient,
+ * and then transitions to a low-pass filter.  The DC removal follows the carrier estimate closely.  The gain reference
+ * rises with the carrier but falls slowly so that when the carrier drops, the remaining noise isn't amplified to full
+ * scale before the squelch closes.
+ */
+public class AmAudioNormalizer
+{
+    private static final double CARRIER_CUTOFF_HERTZ = 10.0;
+    private static final double GAIN_DECAY_SECONDS = 2.0;
+
+    /**
+     * Gain reference limit, approximately -80 dBFS, that sets the maximum applied gain.
+     */
+    private static final float MINIMUM_CARRIER_LEVEL = 1E-4f;
+
+    /**
+     * Audio amplitude produced by 100% modulation.
+     */
+    private static final float FULL_MODULATION_AMPLITUDE = 0.75f;
+    private static final float MAXIMUM_AMPLITUDE = 0.95f;
+
+    private float mCarrierAlpha;
+    private float mGainDecayAlpha;
+    private int mSettlingSamples;
+    private int mSampleCount;
+    private float mCarrier;
+    private float mGainReference;
+
+    /**
+     * Constructs an instance
+     * @param sampleRate of the envelope samples in hertz
+     */
+    public AmAudioNormalizer(double sampleRate)
+    {
+        setSampleRate(sampleRate);
+    }
+
+    /**
+     * Sets the sample rate and resets this normalizer.
+     * @param sampleRate of the envelope samples in hertz
+     */
+    public void setSampleRate(double sampleRate)
+    {
+        mCarrierAlpha = (float)(1.0 - Math.exp(-2.0 * Math.PI * CARRIER_CUTOFF_HERTZ / sampleRate));
+        mGainDecayAlpha = (float)(1.0 - Math.exp(-1.0 / (GAIN_DECAY_SECONDS * sampleRate)));
+        mSettlingSamples = (int)Math.ceil(1.0 / mCarrierAlpha);
+        reset();
+    }
+
+    /**
+     * Resets this normalizer to prepare for a new transmission.
+     */
+    public void reset()
+    {
+        mSampleCount = 0;
+        mCarrier = 0.0f;
+        mGainReference = 0.0f;
+    }
+
+    /**
+     * Converts the envelope sample to an audio sample.
+     * @param envelope sample, unscaled
+     * @return audio sample limited to the audio amplitude range.
+     */
+    public float process(float envelope)
+    {
+        if(mSampleCount < mSettlingSamples)
+        {
+            mSampleCount++;
+            mCarrier += (envelope - mCarrier) / mSampleCount;
+            mGainReference = mCarrier;
+        }
+        else
+        {
+            mCarrier += (envelope - mCarrier) * mCarrierAlpha;
+
+            if(mCarrier > mGainReference)
+            {
+                mGainReference = mCarrier;
+            }
+            else
+            {
+                mGainReference += (mCarrier - mGainReference) * mGainDecayAlpha;
+            }
+        }
+
+        float audio = (envelope - mCarrier) / Math.max(mGainReference, MINIMUM_CARRIER_LEVEL) * FULL_MODULATION_AMPLITUDE;
+        return Math.clamp(audio, -MAXIMUM_AMPLITUDE, MAXIMUM_AMPLITUDE);
+    }
+}

src/main/java/io/github/dsheirer/dsp/am/AmDemodulatorFactory.java

@@ -51,8 +51,6 @@ public class AmDemodulatorFactory
                 return new VectorAMDemodulator256(gain);
             case VECTOR_SIMD_512:
                 return new VectorAMDemodulator512(gain);
-            case VECTOR_SIMD_PREFERRED:
-                return new VectorAMDemodulator64(gain);
             case SCALAR:
             case UNCALIBRATED:
                 return new ScalarAMDemodulator(gain);

src/main/java/io/github/dsheirer/dsp/am/ISquelchingDemodulator.java

@@ -17,13 +17,14 @@
  * ****************************************************************************
  */
 
-package io.github.dsheirer.dsp.fm;
+package io.github.dsheirer.dsp.am;
 
+import io.github.dsheirer.dsp.fm.IDemodulator;
 import io.github.dsheirer.sample.Listener;
 import io.github.dsheirer.source.SourceEvent;
 
 /**
- * Interface for FM demodulator that provides squelch control.
+ * Interface for AM demodulator that provides squelch control.
  */
 public interface ISquelchingDemodulator extends IDemodulator
 {

src/main/java/io/github/dsheirer/dsp/am/SquelchingAMDemodulator.java

@@ -19,7 +19,6 @@
 
 package io.github.dsheirer.dsp.am;
 
-import io.github.dsheirer.dsp.fm.ISquelchingDemodulator;
 import io.github.dsheirer.dsp.magnitude.IMagnitudeCalculator;
 import io.github.dsheirer.dsp.magnitude.MagnitudeFactory;
 import io.github.dsheirer.dsp.squelch.AdaptiveSquelch;
@@ -32,32 +31,63 @@ import io.github.dsheirer.source.SourceEvent;
 public class SquelchingAMDemodulator implements ISquelchingDemodulator, Listener<SourceEvent>
 {
     private static final float ZERO = 0.0f;
+    private static final float ENVELOPE_GAIN = 1.0f;
+    private static final double DEFAULT_SAMPLE_RATE = 50000.0;
+    private static final double FADE_SECONDS = 0.005;
+
+    /**
+     * Audio delay, longer than the worst case 25 ms for the squelch to detect loss of signal plus the fade duration, so
+     * that the audio fades out before the carrier drop reaches the audio normalizer, which would otherwise produce a
+     * thump at the end of a transmission.
+     */
+    private static final double AUDIO_DELAY_SECONDS = 0.032;
     private final IMagnitudeCalculator mMagnitudeCalculator = MagnitudeFactory.getMagnitudeCalculator();
     private final IAmDemodulator mAmDemodulator;
     private final AdaptiveSquelch mAdaptiveSquelch;
+    private final AmAudioNormalizer mAudioNormalizer = new AmAudioNormalizer(DEFAULT_SAMPLE_RATE);
+    private float[] mDelayedEnvelope;
+    private boolean[] mDelayedAudioEnabled;
+    private int mDelayPointer = 0;
+    private float mFadeGain = 0.0f;
+    private float mFadeStep = (float)(1.0 / (DEFAULT_SAMPLE_RATE * FADE_SECONDS));
     private boolean mSquelchChanged = false;
 
     /**
      * Constructs an instance
-     * @param gain to apply to the demodulated AM samples (e.g. 500.0f)
-     * @param alpha decay value of the single pole IIR filter in range: 0.0 - 1.0.  The smaller the alpha value,
-     * the slower the squelch response.
      * @param squelchThreshold in decibels.  Signal power must exceed this threshold value for unsquelch.
      * @param squelchAutoTrack to enable the squelch noise floor auto tracking feature.
+     * @param bandwidth of the channel in hertz
      */
-    public SquelchingAMDemodulator(float gain, float alpha, float squelchThreshold, boolean squelchAutoTrack)
+    public SquelchingAMDemodulator(float squelchThreshold, boolean squelchAutoTrack, double bandwidth)
     {
-        mAmDemodulator = AmDemodulatorFactory.getAmDemodulator(gain);
-        mAdaptiveSquelch = new AdaptiveSquelch(alpha, squelchThreshold, squelchAutoTrack);
+        mAmDemodulator = AmDemodulatorFactory.getAmDemodulator(ENVELOPE_GAIN);
+        mAdaptiveSquelch = new AdaptiveSquelch(squelchThreshold, squelchAutoTrack, bandwidth);
+        setAudioDelay(DEFAULT_SAMPLE_RATE);
     }
 
     /**
-     * Set or update the sample rate for the squelch to adjust the power level notification rate.
+     * Set or update the sample rate for the squelch to adjust the power level notification rate and for the audio
+     * normalizer timing.
      * @param sampleRate in hertz
      */
     public void setSampleRate(int sampleRate)
     {
         mAdaptiveSquelch.setSampleRate(sampleRate);
+        mAudioNormalizer.setSampleRate(sampleRate);
+        mFadeStep = (float)Math.min(1.0, 1.0 / (sampleRate * FADE_SECONDS));
+        setAudioDelay(sampleRate);
+    }
+
+    /**
+     * Sizes the audio delay buffers.
+     * @param sampleRate in hertz
+     */
+    private void setAudioDelay(double sampleRate)
+    {
+        int length = (int)Math.ceil(sampleRate * AUDIO_DELAY_SECONDS);
+        mDelayedEnvelope = new float[length];
+        mDelayedAudioEnabled = new boolean[length];
+        mDelayPointer = 0;
     }
 
     /**
@@ -72,7 +102,7 @@ public class SquelchingAMDemodulator implements ISquelchingDemodulator, Listener
      * Demodulates the complex sample arrays.
      * @param i inphase sample array
      * @param q quadrature sample array
-     * @return demodulated AM samples with gain applied.
+     * @return demodulated audio samples, normalized to the carrier level, or zero valued samples while squelched.
      */
     public float[] demodulate(float[] i, float[] q)
     {
@@ -86,9 +116,26 @@ public class SquelchingAMDemodulator implements ISquelchingDemodulator, Listener
         {
             mAdaptiveSquelch.process(magnitude[x]);
 
-            if(!(mAdaptiveSquelch.isUnmuted()))
+            boolean audioEnabled = mAdaptiveSquelch.isAudioEnabled();
+            float envelope = mDelayedEnvelope[mDelayPointer];
+            boolean delayedAudioEnabled = mDelayedAudioEnabled[mDelayPointer];
+            mDelayedEnvelope[mDelayPointer] = demodulated[x];
+            mDelayedAudioEnabled[mDelayPointer] = audioEnabled;
+            mDelayPointer = (mDelayPointer + 1) % mDelayedEnvelope.length;
+
+            //Fade in once the delayed audio reaches the squelch open point and fade out as soon as the squelch detects
+            //loss of signal, ahead of the delayed audio.
+            mFadeGain = (audioEnabled && delayedAudioEnabled) ? Math.min(mFadeGain + mFadeStep, 1.0f) :
+                    Math.max(mFadeGain - mFadeStep, 0.0f);
+
+            if(mFadeGain > ZERO)
+            {
+                demodulated[x] = mAudioNormalizer.process(envelope) * mFadeGain;
+            }
+            else
             {
                 demodulated[x] = ZERO;
+                mAudioNormalizer.reset();
             }
 
             if(mAdaptiveSquelch.isSquelchChanged())

src/main/java/io/github/dsheirer/dsp/am/VectorAMDemodulator128.java

@@ -18,8 +18,6 @@
  */
 package io.github.dsheirer.dsp.am;
 
-import io.github.dsheirer.dsp.magnitude.IMagnitudeCalculator;
-import io.github.dsheirer.dsp.magnitude.MagnitudeFactory;
 import io.github.dsheirer.vector.VectorUtilities;
 import jdk.incubator.vector.FloatVector;
 import jdk.incubator.vector.VectorSpecies;
@@ -32,7 +30,6 @@ public class VectorAMDemodulator128 implements IAmDemodulator
 {
     private static final VectorSpecies<Float> VECTOR_SPECIES = FloatVector.SPECIES_128;
     private float mGain;
-    private IMagnitudeCalculator mMagnitudeCalculator = MagnitudeFactory.getMagnitudeCalculator();
 
     /**
      * Constructs this demodulator where the specified gain is applied to demodulated output samples.

src/main/java/io/github/dsheirer/dsp/am/VectorAMDemodulator256.java

@@ -18,8 +18,6 @@
  */
 package io.github.dsheirer.dsp.am;
 
-import io.github.dsheirer.dsp.magnitude.IMagnitudeCalculator;
-import io.github.dsheirer.dsp.magnitude.MagnitudeFactory;
 import io.github.dsheirer.vector.VectorUtilities;
 import jdk.incubator.vector.FloatVector;
 import jdk.incubator.vector.VectorSpecies;
@@ -32,7 +30,6 @@ public class VectorAMDemodulator256 implements IAmDemodulator
 {
     private static final VectorSpecies<Float> VECTOR_SPECIES = FloatVector.SPECIES_256;
     private float mGain;
-    private IMagnitudeCalculator mMagnitudeCalculator = MagnitudeFactory.getMagnitudeCalculator();
 
     /**
      * Constructs this demodulator where the specified gain is applied to demodulated output samples.

src/main/java/io/github/dsheirer/dsp/am/VectorAMDemodulator512.java

@@ -18,8 +18,6 @@
  */
 package io.github.dsheirer.dsp.am;
 
-import io.github.dsheirer.dsp.magnitude.IMagnitudeCalculator;
-import io.github.dsheirer.dsp.magnitude.MagnitudeFactory;
 import io.github.dsheirer.vector.VectorUtilities;
 import jdk.incubator.vector.FloatVector;
 import jdk.incubator.vector.VectorSpecies;
@@ -32,7 +30,6 @@ public class VectorAMDemodulator512 implements IAmDemodulator
 {
     private static final VectorSpecies<Float> VECTOR_SPECIES = FloatVector.SPECIES_512;
     private float mGain;
-    private IMagnitudeCalculator mMagnitudeCalculator = MagnitudeFactory.getMagnitudeCalculator();
 
     /**
      * Constructs this demodulator where the specified gain is applied to demodulated output samples.

src/main/java/io/github/dsheirer/dsp/am/VectorAMDemodulator64.java

@@ -18,8 +18,6 @@
  */
 package io.github.dsheirer.dsp.am;
 
-import io.github.dsheirer.dsp.magnitude.IMagnitudeCalculator;
-import io.github.dsheirer.dsp.magnitude.MagnitudeFactory;
 import io.github.dsheirer.vector.VectorUtilities;
 import jdk.incubator.vector.FloatVector;
 import jdk.incubator.vector.VectorSpecies;
@@ -32,7 +30,6 @@ public class VectorAMDemodulator64 implements IAmDemodulator
 {
     private static final VectorSpecies<Float> VECTOR_SPECIES = FloatVector.SPECIES_64;
     private float mGain;
-    private IMagnitudeCalculator mMagnitudeCalculator = MagnitudeFactory.getMagnitudeCalculator();
 
     /**
      * Constructs this demodulator where the specified gain is applied to demodulated output samples.

src/main/java/io/github/dsheirer/dsp/filter/ChannelFilterDesigner.java

@@ -0,0 +1,148 @@
+/*
+ * *****************************************************************************
+ * Copyright (C) 2014-2026 Dennis Sheirer
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program.  If not, see <http://www.gnu.org/licenses/>
+ * ****************************************************************************
+ */
+package io.github.dsheirer.dsp.filter;
+
+import io.github.dsheirer.dsp.filter.design.FilterDesignException;
+import io.github.dsheirer.dsp.filter.fir.FIRFilterSpecification;
+import io.github.dsheirer.dsp.window.WindowType;
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
+
+/**
+ * Designs low-pass filters for complex sample channels, with a check of the designed frequency response.
+ */
+public class ChannelFilterDesigner
+{
+    private static final Logger LOGGER = LoggerFactory.getLogger(ChannelFilterDesigner.class);
+    private static final double MAXIMUM_STOP_BAND_DB = -40.0;
+    private static final double MAXIMUM_PASS_BAND_DB = 1.0;
+    private static final int FILTER_RESPONSE_CHECK_POINTS = 1024;
+    private static final int FALLBACK_FILTER_SIZING_ATTENUATION_DB = 75;
+    private static final int FALLBACK_FILTER_MAXIMUM_ATTENUATION_DB = 150;
+    private static final int FALLBACK_FILTER_ATTENUATION_STEP_DB = 15;
+
+    /**
+     * Designs the low-pass channel filter for complex samples, where the channel bandwidth spans the two-sided
+     * (positive and negative frequency) signal.  The stop band ripple provides approximately 46 dB of attenuation.
+     *
+     * The remez designer can converge on a filter that meets the specification at the design grid points but has a large
+     * response spike outside of them, so the response of the designed filter is checked before it's used.
+     *
+     * @param sampleRate of the samples to filter in hertz
+     * @param bandwidth of the channel in hertz
+     * @return filter coefficients
+     */
+    public static float[] design(double sampleRate, double bandwidth)
+    {
+        int passBandStop = (int)(bandwidth * .4);
+        int stopBandStart = (int)(bandwidth * .5);
+
+        FIRFilterSpecification specification = FIRFilterSpecification.lowPassBuilder()
+                .sampleRate(sampleRate)
+                .gridDensity(16)
+                .oddLength(true)
+                .passBandCutoff(passBandStop)
+                .passBandAmplitude(1.0)
+                .passBandRipple(0.01)
+                .stopBandStart(stopBandStart)
+                .stopBandAmplitude(0.0)
+                .stopBandRipple(0.005)
+                .build();
+
+        float[] coefficients = null;
+
+        try
+        {
+            coefficients = FilterFactory.getTaps(specification);
+        }
+        catch(FilterDesignException fde)
+        {
+            LOGGER.warn("Couldn't design remez channel filter for sample rate [" + sampleRate +
+                    "] pass frequency [" + passBandStop + "] and stop frequency [" + stopBandStart + "]");
+        }
+
+        if(coefficients == null || !isValidFilterResponse(coefficients, sampleRate, passBandStop, stopBandStart))
+        {
+            LOGGER.info("Unable to use remez filter designer for sample rate [" + sampleRate + "] pass band stop [" +
+                    passBandStop + "] and stop band start [" + stopBandStart +
+                    "] - will proceed using simple low pass filter design");
+            //Center the cutoff so the bandwidth matches the remez design and size the filter to meet the response limits.
+            for(int attenuation = FALLBACK_FILTER_SIZING_ATTENUATION_DB; attenuation <= FALLBACK_FILTER_MAXIMUM_ATTENUATION_DB;
+                attenuation += FALLBACK_FILTER_ATTENUATION_STEP_DB)
+            {
+                int length = FilterFactory.getLowPass(sampleRate, passBandStop, stopBandStart, attenuation,
+                        WindowType.HAMMING, true).length;
+                coefficients = FilterFactory.getLowPass(sampleRate, (passBandStop + stopBandStart) / 2, length, WindowType.HAMMING);
+
+                if(isValidFilterResponse(coefficients, sampleRate, passBandStop, stopBandStart))
+                {
+                    break;
+                }
+            }
+        }
+
+        return coefficients;
+    }
+
+    /**
+     * Checks the frequency response of the low-pass filter, relative to the response at DC.
+     * @param coefficients of the filter
+     * @param sampleRate of the filter in hertz
+     * @param passBandStop frequency in hertz
+     * @param stopBandStart frequency in hertz
+     * @return true if the pass band and stop band responses are within limits, through to half the sample rate.
+     */
+    public static boolean isValidFilterResponse(float[] coefficients, double sampleRate, int passBandStop, int stopBandStart)
+    {
+        double dc = getResponseDb(coefficients, 0.0, sampleRate);
+        double nyquist = sampleRate / 2.0;
+
+        for(int x = 0; x <= FILTER_RESPONSE_CHECK_POINTS; x++)
+        {
+            double frequency = nyquist * x / FILTER_RESPONSE_CHECK_POINTS;
+            double response = getResponseDb(coefficients, frequency, sampleRate) - dc;
+
+            if((frequency <= passBandStop && response > MAXIMUM_PASS_BAND_DB) ||
+               (frequency >= stopBandStart && response > MAXIMUM_STOP_BAND_DB))
+            {
+                return false;
+            }
+        }
+
+        return true;
+    }
+
+    /**
+     * Calculates the magnitude response of the filter at the specified frequency.
+     */
+    public static double getResponseDb(float[] coefficients, double frequency, double sampleRate)
+    {
+        double radians = 2.0 * Math.PI * frequency / sampleRate;
+        double real = 0.0;
+        double imaginary = 0.0;
+
+        for(int x = 0; x < coefficients.length; x++)
+        {
+            real += coefficients[x] * Math.cos(radians * x);
+            imaginary += coefficients[x] * Math.sin(radians * x);
+        }
+
+        return 20.0 * Math.log10(Math.hypot(real, imaginary));
+    }
+}

src/main/java/io/github/dsheirer/dsp/filter/channelizer/ComplexPolyphaseChannelizerM2.java

@@ -27,7 +27,7 @@ import java.util.Arrays;
 import java.util.Queue;
 import java.util.concurrent.ArrayBlockingQueue;
 import org.apache.commons.math3.util.FastMath;
-import org.jtransforms.fft.FloatFFT_1D;
+import org.jtransforms.fft.ReusableFloatInverseFFT;
 import org.slf4j.Logger;
 import org.slf4j.LoggerFactory;
 
@@ -85,7 +85,7 @@ public class ComplexPolyphaseChannelizerM2 extends AbstractComplexPolyphaseChann
 
     //Sized to process 40 times per second
     private IFFTProcessorDispatcher mIFFTProcessorDispatcher = new IFFTProcessorDispatcher(25);
-    private FloatFFT_1D mFFT;
+    private ReusableFloatInverseFFT mFFT;
     private ChannelDFT mChannelDFT;
     private float[] mInlineSamples;
     private float[] mInlineFilter;
@@ -453,7 +453,7 @@ public class ComplexPolyphaseChannelizerM2 extends AbstractComplexPolyphaseChann
     private void init(float[] coefficients)
     {
         int channelCount = getChannelCount();
-        mFFT = new FloatFFT_1D(channelCount);
+        mFFT = new ReusableFloatInverseFFT(channelCount);
         mChannelDFT = ChannelDFTFactory.getChannelDFT(channelCount);
         int bufferLength = getSubChannelCount() * mTapsPerChannel;
         mSamplesPerBlock = channelCount; //Same as subChannelCount / 2
@@ -505,7 +505,7 @@ public class ComplexPolyphaseChannelizerM2 extends AbstractComplexPolyphaseChann
                         for(int offset = 0; offset < samples.length; offset += blockLength)
                         {
                             //Rotate each of the channels to the correct phase using the IFFT
-                            mFFT.complexInverse(samples, offset, true);
+                            mFFT.complexInverse(samples, offset);
                         }
                     }
 

src/main/java/io/github/dsheirer/dsp/filter/fir/remez/RemezFIRFilterDesigner.java

@@ -100,7 +100,7 @@ public class RemezFIRFilterDesigner
     	}
     	catch( FilterDesignException fde )
     	{
-    		mLog.error( "Filter design error - couldn't find extremal indices at count [" + 
+    		mLog.warn( "Filter design error - couldn't find extremal indices at count [" + 
     				iterationCount + "] try changing filter order up/down from [" +
     				mSpecification.getOrder() + "]" );
     		

src/main/java/io/github/dsheirer/dsp/fm/SquelchingFMDemodulator.java

@@ -1,161 +0,0 @@
-/*
- * *****************************************************************************
- * Copyright (C) 2014-2023 Dennis Sheirer
- *
- * This program is free software: you can redistribute it and/or modify
- * it under the terms of the GNU General Public License as published by
- * the Free Software Foundation, either version 3 of the License, or
- * (at your option) any later version.
- *
- * This program is distributed in the hope that it will be useful,
- * but WITHOUT ANY WARRANTY; without even the implied warranty of
- * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
- * GNU General Public License for more details.
- *
- * You should have received a copy of the GNU General Public License
- * along with this program.  If not, see <http://www.gnu.org/licenses/>
- * ****************************************************************************
- */
-
-package io.github.dsheirer.dsp.fm;
-
-import io.github.dsheirer.dsp.magnitude.IMagnitudeCalculator;
-import io.github.dsheirer.dsp.magnitude.MagnitudeFactory;
-import io.github.dsheirer.dsp.squelch.AdaptiveSquelch;
-import io.github.dsheirer.sample.Listener;
-import io.github.dsheirer.source.SourceEvent;
-import org.slf4j.Logger;
-import org.slf4j.LoggerFactory;
-
-/**
- * FM Demodulator for demodulating complex samples and producing demodulated floating point samples.
- *
- * Implements listener of source events to process runtime squelch threshold change request events
- * which are forwarded to the power squelch control.
- */
-public class SquelchingFMDemodulator implements ISquelchingDemodulator, Listener<SourceEvent>
-{
-    private static final Logger mLog = LoggerFactory.getLogger(SquelchingFMDemodulator.class);
-    private static final float ZERO = 0.0f;
-    private final AdaptiveSquelch mAdaptiveSquelch;
-    private final IMagnitudeCalculator mMagnitude = MagnitudeFactory.getMagnitudeCalculator();
-    private final IDemodulator mFmDemodulator = FmDemodulatorFactory.getFmDemodulator();
-    private boolean mSquelchChanged = false;
-
-    /**
-     * Creates an FM demodulator instance with a default gain of 1.0.
-     *
-     * @param alpha decay value of the single pole IIR filter in range: 0.0 - 1.0.  The smaller the alpha value,
-     * the slower the squelch response.
-     * @param squelchThreshold in decibels.  Signal power must exceed this threshold value for unsquelch.
-     * causes immediate mute and unmute.  Set to higher count to prevent mute/unmute flapping.
-     * @param squelchAutoTrack to enable the squelch noise floor auto-tracking feature.
-     */
-    public SquelchingFMDemodulator(float alpha, float squelchThreshold, boolean squelchAutoTrack)
-    {
-        mAdaptiveSquelch = new AdaptiveSquelch(alpha, squelchThreshold, squelchAutoTrack);
-    }
-
-    /**
-     * Set or update the sample rate for the squelch to adjust the power level notification rate.
-     * @param sampleRate in hertz
-     */
-    public void setSampleRate(int sampleRate)
-    {
-        mAdaptiveSquelch.setSampleRate(sampleRate);
-    }
-
-    /**
-     * Registers the listener to receive notifications of squelch change events from the power squelch.
-     */
-    public void setSourceEventListener(Listener<SourceEvent> listener)
-    {
-        mAdaptiveSquelch.setSourceEventListener(listener);
-    }
-
-    /**
-     * Demodulates the complex (I/Q) sample arrays
-     * @param i inphase samples
-     * @param q quadrature samples
-     * @return demodulated real samples
-     */
-    @Override
-    public float[] demodulate(float[] i, float[] q)
-    {
-        setSquelchChanged(false);
-
-        float[] demodulated = mFmDemodulator.demodulate(i, q);
-        float[] magnitude = mMagnitude.calculate(i, q);
-
-        for(int x = 0; x < magnitude.length; x++)
-        {
-            mAdaptiveSquelch.process(magnitude[x]);
-
-            if(!(mAdaptiveSquelch.isUnmuted()))
-            {
-                demodulated[x] = ZERO;
-            }
-
-            if(mAdaptiveSquelch.isSquelchChanged())
-            {
-                setSquelchChanged(true);
-            }
-        }
-
-        return demodulated;
-    }
-
-    /**
-     * Sets the threshold for squelch control
-     * @param threshold (dB)
-     */
-    public void setSquelchThreshold(float threshold)
-    {
-        mAdaptiveSquelch.setSquelchThreshold(threshold);
-    }
-
-    @Override
-    public void setSquelchAutoTrack(boolean autoTrack)
-    {
-        mAdaptiveSquelch.setSquelchAutoTrack(autoTrack);
-    }
-
-    /**
-     * Indicates if the squelch state has changed during the processing of buffer(s)
-     */
-    public boolean isSquelchChanged()
-    {
-        return mSquelchChanged;
-    }
-
-    /**
-     * Sets or resets the squelch changed flag.
-     */
-    private void setSquelchChanged(boolean changed)
-    {
-        mSquelchChanged = changed;
-    }
-
-    /**
-     * Indicates if the squelch state is currently muted
-     */
-    public boolean isMuted()
-    {
-        return mAdaptiveSquelch.isMuted();
-    }
-
-    @Override
-    public void receive(SourceEvent sourceEvent)
-    {
-        switch(sourceEvent.getEvent())
-        {
-            //Only forward squelch threshold and auto-track current & change requests
-            case REQUEST_CURRENT_SQUELCH_THRESHOLD:
-            case REQUEST_CHANGE_SQUELCH_THRESHOLD:
-            case REQUEST_CURRENT_SQUELCH_AUTO_TRACK:
-            case REQUEST_CHANGE_SQUELCH_AUTO_TRACK:
-                mAdaptiveSquelch.receive(sourceEvent);
-                break;
-        }
-    }
-}

src/main/java/io/github/dsheirer/dsp/squelch/AdaptiveSquelch.java

@@ -19,66 +19,106 @@
 
 package io.github.dsheirer.dsp.squelch;
 
-import io.github.dsheirer.dsp.filter.iir.SinglePoleIirFilter;
 import io.github.dsheirer.sample.Listener;
 import io.github.dsheirer.source.SourceEvent;
-import java.time.Duration;
+import java.util.Arrays;
 import org.apache.commons.math3.util.FastMath;
 import org.slf4j.Logger;
 import org.slf4j.LoggerFactory;
 
 /**
- * Adaptive squelch control that optionally tracks the noise floor and auto-adjusts squelch threshold.
+ * Adaptive power squelch control that optionally tracks the noise floor and auto-adjusts squelch threshold.
+ *
+ * Signal power is measured in 5 millisecond blocks so that all timing is independent of the sample rate.  The squelch
+ * opens after consecutive blocks at or above the threshold.  It closes on a 20 millisecond power average that spans at
+ * least one cycle of the lowest voice frequencies, so that modulation doesn't look like a loss of signal, and which
+ * responds in a fixed time regardless of how strong the signal was.
+ *
+ * Closing occurs in two steps.  Audio is disabled as soon as the power average falls below the close threshold, which
+ * limits the noise tail, while the squelch stays open for a hang period to bridge a brief signal fade without ending
+ * the call.
+ *
+ * When auto-track is enabled, the noise floor is the lowest power from the recent intervals that look like noise, using
+ * the ratio mean(power^2) / mean(power)^2, which is 2.0 for gaussian noise and approaches 1.0 for a steady carrier.  The
+ * threshold is held at a margin over the noise floor, so a threshold below the noise floor can't latch the squelch open.
+ * The squelch stays closed until the first noise floor measurement is complete.  A signal that doesn't look like noise
+ * is excluded from the noise floor unless it persists for the carrier timeout, after which it's treated as the noise
+ * floor so that a dead carrier doesn't hold the squelch open.  The noise floor recovers when the carrier ends.  A carrier
+ * with voice modulation, such as a continuous broadcast, doesn't time out, and a timed out carrier that develops voice
+ * modulation is removed from the noise floor.
  *
  * Initially modeled on: https://github.com/gnuradio/gnuradio/blob/master/gr-analog/lib/simple_squelch_cc_impl.cc
  */
 public class AdaptiveSquelch implements Listener<SourceEvent>
 {
     private static final Logger mLog = LoggerFactory.getLogger(AdaptiveSquelch.class);
-    private static final long AUTO_ADJUST_PERIOD_MS = Duration.ofSeconds(5).toMillis();
-    private SinglePoleIirFilter mFilter;
+    private static final double DEFAULT_SAMPLE_RATE = 50000.0;
+    private static final double BLOCK_SECONDS = 0.005;
+    private static final int OPEN_BLOCKS = 2; //10 milliseconds
+    private static final int CLOSE_AVERAGE_BLOCKS = 4; //20 milliseconds
+    private static final int HANG_BLOCKS = 20; //100 milliseconds
+    private static final int POWER_INTERVAL_BLOCKS = 100; //500 milliseconds
+    private static final int NOISE_WINDOW_INTERVALS = 20; //10 seconds
+    private static final int CARRIER_TIMEOUT_INTERVALS = 120; //60 seconds
+    private static final int MINIMUM_VOICE_INTERVALS = 3;
+    private static final double NOISE_POWER_RATIO = 1.85;
+    private static final float MINIMUM_SQUELCH_MARGIN = 4.0f; //6 dB
+    private static final float CLOSE_THRESHOLD_RATIO = 0.5f; //3 dB below the open threshold
+    private final float[] mCloseBlocks = new float[CLOSE_AVERAGE_BLOCKS];
+    private int mCloseBlockPointer = 0;
+    private float mCloseAccumulator = 0.0f;
+    private int mBlockSize = (int)Math.round(DEFAULT_SAMPLE_RATE * BLOCK_SECONDS);
+    private int mBlockSampleCount = 0;
+    private float mBlockAccumulator = 0.0f;
+    private int mOpenCount = 0;
+    private int mHangCount = 0;
     private float mPower = 0.0f;
-    private boolean mSquelch;
-    private float mSquelchThreshold;
+    private double mIntervalPower = 0.0;
+    private double mIntervalPowerSquared = 0.0;
+    private int mIntervalSampleCount = 0;
+    private int mIntervalBlockCount = 0;
+    private boolean mFirstIntervalComplete = false;
+    private final float[] mNoiseHistory = new float[NOISE_WINDOW_INTERVALS];
+    private int mNoiseHistoryPointer = 0;
+    private int mNoiseHistoryCount = 0;
+    private int mCarrierIntervalCount = 0;
+    private int mVoiceIntervalCount = 0;
+    private boolean mCarrierTimedOut = false;
+    private boolean mCarrierDetected = false;
+    private Float mNoiseFloorBeforeCarrier;
+    private final VoiceModulationDetector mVoiceModulationDetector;
     private Float mNoiseFloor;
-    private float mSquelchBuffer;
+    private Float mLowestNoiseFloor;
+    private float mUserThreshold;
+    private boolean mSquelch = true;
+    private float mSquelchThreshold;
     private boolean mSquelchChanged = false;
-    private int mPowerLevelBroadcastCount = 0;
-    private int mPowerLevelBroadcastThreshold;
     private boolean mAutoTrackNoiseFloor;
-    private long mLastAutoAdjustTimestamp;
     private Listener<SourceEvent> mSourceEventListener;
 
     /**
      * Constructs an instance
      *
-     * Testing against a 12.5 kHz analog FM modulated signal, the following parameters provided a
-     * good responsiveness.  A threshold of -80.0 dB seemed to trigger significant flapping during un-squelching.
-     *   - alpha: 0.0001
-     *   - threshold: 78.0 dB
-     *
-     * @param alpha decay value of the single pole IIR filter in range: 0.0 - 1.0.  The smaller the alpha value,
-     * the slower the squelch response.
      * @param squelchThreshold in decibels.  Signal power must exceed this threshold value for unsquelch.
      * @param autoTrack the noise floor when squelched and periodically readjust the squelch threshold.
+     * @param bandwidth of the channel in hertz
      */
-    public AdaptiveSquelch(float alpha, float squelchThreshold, boolean autoTrack)
+    public AdaptiveSquelch(float squelchThreshold, boolean autoTrack, double bandwidth)
     {
-        mFilter = new SinglePoleIirFilter(alpha);
+        mVoiceModulationDetector = new VoiceModulationDetector(DEFAULT_SAMPLE_RATE, bandwidth,
+                (int)Math.round(DEFAULT_SAMPLE_RATE * BLOCK_SECONDS) * POWER_INTERVAL_BLOCKS);
         setSquelchThreshold(squelchThreshold);
         mAutoTrackNoiseFloor = autoTrack;
-        mLastAutoAdjustTimestamp = System.currentTimeMillis();
-        mPowerLevelBroadcastThreshold = 25000; //Based on a default sample rate of 50 kHz, so 2x/second
     }
 
     /**
-     * Sets the sample rate to effect the frequency of power level notifications where the notifications are
-     * sent twice a second.
+     * Sets the sample rate to size the power measurement blocks.
      * @param sampleRate in hertz
      */
     public void setSampleRate(int sampleRate)
     {
-        mPowerLevelBroadcastThreshold = sampleRate / 2;
+        mBlockSize = Math.max(1, (int)Math.round(sampleRate * BLOCK_SECONDS));
+        mVoiceModulationDetector.configure(sampleRate, mBlockSize * POWER_INTERVAL_BLOCKS);
     }
 
     /**
@@ -132,32 +172,36 @@ public class AdaptiveSquelch implements Listener<SourceEvent>
     }
 
     /**
-     * Sets the squelch threshold
+     * Sets the squelch threshold.  With auto-track enabled, the threshold is treated as a margin over the current noise
+     * floor, subject to the minimum squelch margin.  The margin is stored relative to the lowest observed noise floor so
+     * that a change made while a timed out carrier has raised the noise floor applies once that carrier ends.
      * @param squelchThreshold in decibels
      */
     public void setSquelchThreshold(float squelchThreshold)
     {
-        float squelchThresholdDb = fromDb(squelchThreshold);
-        setSquelchThreshold(squelchThresholdDb, true);
+        float threshold = fromDb(squelchThreshold);
+
+        if(mAutoTrackNoiseFloor && mNoiseFloor != null)
+        {
+            mUserThreshold = mLowestNoiseFloor * Math.max(MINIMUM_SQUELCH_MARGIN, threshold / mNoiseFloor);
+            updateTrackedThreshold();
+        }
+        else
+        {
+            mUserThreshold = threshold;
+            applySquelchThreshold(mUserThreshold);
+        }
     }
 
     /**
-     * Sets the squelch threshold.  This method is synchronized to coordinate changes requested by the user/UI thread
+     * Applies the squelch threshold.  This method is synchronized to coordinate changes requested by the user/UI thread
      * and auto-track changes made by the stream processing thread.
      *
      * @param squelchThreshold value
-     * @param resetNoiseFloor to reset the noise floor and squelch threshold
      */
-    private synchronized void setSquelchThreshold(float squelchThreshold, boolean resetNoiseFloor)
+    private synchronized void applySquelchThreshold(float squelchThreshold)
     {
         mSquelchThreshold = squelchThreshold;
-
-        if(resetNoiseFloor)
-        {
-            //Set noise floor to null so that both the noise floor and the squelch buffer get updated after first power reading
-            mNoiseFloor = null;
-        }
-
         broadcast(SourceEvent.squelchThreshold(null, getSquelchThreshold()));
     }
 
@@ -183,59 +227,231 @@ public class AdaptiveSquelch implements Listener<SourceEvent>
     }
 
     /**
-     * Processes a complex IQ sample and changes squelch state when the signal power is above or below the
-     * threshold value.
+     * Processes a complex IQ sample and updates the squelch state at the end of each power measurement block.
      * @param magnitude of a complex sample (inphase * inphase + quadrature * quadrature)
      */
     public void process(float magnitude)
     {
-        mPower = mFilter.filter(magnitude);
+        mBlockAccumulator += magnitude;
+        mBlockSampleCount++;
+        mIntervalPower += magnitude;
+        mIntervalPowerSquared += (double)magnitude * magnitude;
+        mIntervalSampleCount++;
 
-        if(mSquelch && mPower >= mSquelchThreshold)
+        //Voice detection is only needed for a carrier, so that channels with only noise don't incur this cost.
+        if(mCarrierDetected)
         {
-            setSquelch(false);
-        }
-        else if(!mSquelch && mPower < mSquelchThreshold)
-        {
-            setSquelch(true);
+            mVoiceModulationDetector.receive((float)Math.sqrt(magnitude));
         }
 
-        mPowerLevelBroadcastCount++;
-        if(mPowerLevelBroadcastCount % mPowerLevelBroadcastThreshold == 0)
+        if(mBlockSampleCount >= mBlockSize)
         {
-            mPowerLevelBroadcastCount = 0;
-            broadcast(SourceEvent.channelPowerLevel(null, 10.0 * Math.log10(mPower)));
-
-            if(mSquelch)
-            {
-                adjustSquelchThreshold();
-            }
+            float power = mBlockAccumulator / mBlockSampleCount;
+            mBlockAccumulator = 0.0f;
+            mBlockSampleCount = 0;
+            processBlock(power);
         }
     }
 
     /**
-     * With the user specified squelch threshold, establishes a squelch buffer (delta) from the actual noise floor and
-     * then automatically updates the squelch threshold to be the current noise floor plus this threshold value.
-     *
-     * Note: this method should only be invoked from a squelch (true) state.
+     * Updates the squelch state from a block power measurement.
+     * @param power of the block
      */
-    private void adjustSquelchThreshold()
+    private void processBlock(float power)
     {
-        if(mAutoTrackNoiseFloor)
+        mCloseAccumulator += power - mCloseBlocks[mCloseBlockPointer];
+        mCloseBlocks[mCloseBlockPointer] = power;
+        mCloseBlockPointer = (mCloseBlockPointer + 1) % CLOSE_AVERAGE_BLOCKS;
+
+        if(mSquelch)
         {
-            if(mNoiseFloor == null)
+            //With auto-track, the threshold isn't reliable until there's a noise floor measurement.
+            boolean ready = mFirstIntervalComplete || !mAutoTrackNoiseFloor;
+            mOpenCount = (ready && power >= mSquelchThreshold) ? mOpenCount + 1 : 0;
+
+            if(mOpenCount >= OPEN_BLOCKS)
             {
-                //We set the squelch buffer just once, after the squelch threshold is set and noise floor is set to null
-                mSquelchBuffer = mSquelchThreshold - mPower;
+                mOpenCount = 0;
+                mHangCount = 0;
+                //Seed the close average so that it doesn't start with the blocks from before the signal arrived.
+                Arrays.fill(mCloseBlocks, power);
+                mCloseAccumulator = power * CLOSE_AVERAGE_BLOCKS;
+                setSquelch(false);
+            }
+        }
+        else if(mCloseAccumulator / CLOSE_AVERAGE_BLOCKS >= mSquelchThreshold * CLOSE_THRESHOLD_RATIO)
+        {
+            mHangCount = 0;
+        }
+        else
+        {
+            mHangCount++;
+
+            if(mHangCount >= HANG_BLOCKS)
+            {
+                setSquelch(true);
+            }
+        }
+
+        updatePowerInterval();
+    }
+
+    /**
+     * Counts power blocks to provide periodic power level notifications and noise floor updates.
+     */
+    private void updatePowerInterval()
+    {
+        mIntervalBlockCount++;
+
+        if(mIntervalBlockCount >= POWER_INTERVAL_BLOCKS)
+        {
+            double mean = mIntervalPower / mIntervalSampleCount;
+            mPower = (float)mean;
+            broadcast(SourceEvent.channelPowerLevel(null, 10.0 * Math.log10(mPower)));
+
+            if(mAutoTrackNoiseFloor && mean > 0.0)
+            {
+                updateNoiseFloor(mIntervalPowerSquared / mIntervalSampleCount / (mean * mean));
             }
 
-            mNoiseFloor = mPower;
+            mFirstIntervalComplete = true;
+            mIntervalPower = 0.0;
+            mIntervalPowerSquared = 0.0;
+            mIntervalSampleCount = 0;
+            mIntervalBlockCount = 0;
+        }
+    }
 
-            if((System.currentTimeMillis() - mLastAutoAdjustTimestamp) > AUTO_ADJUST_PERIOD_MS)
-            {
-                setSquelchThreshold(mNoiseFloor + mSquelchBuffer, false);
-                mLastAutoAdjustTimestamp = System.currentTimeMillis();
-            }
+    /**
+     * Updates the noise floor history from the current interval power and updates the squelch threshold.
+     * @param powerRatio mean(power^2) / mean(power)^2 for the interval
+     */
+    private void updateNoiseFloor(double powerRatio)
+    {
+        boolean voice = mVoiceModulationDetector.analyze();
+        mCarrierDetected = powerRatio < NOISE_POWER_RATIO;
+
+        if(mCarrierDetected)
+        {
+            updateCarrier(voice);
+        }
+        else
+        {
+            resetCarrierTracking();
+            mCarrierTimedOut = false;
+            mNoiseFloorBeforeCarrier = null;
+            addNoisePower(mPower);
+        }
+
+        if(mNoiseHistoryCount > 0)
+        {
+            updateTrackedThreshold();
+        }
+    }
+
+    /**
+     * Updates the carrier timeout from an interval that doesn't look like noise.  A carrier that lasts for the timeout
+     * period is treated as the noise floor, unless it has voice modulation.
+     * @param voice true if voice modulation was detected in this interval
+     */
+    private void updateCarrier(boolean voice)
+    {
+        mCarrierIntervalCount++;
+
+        if(voice)
+        {
+            mVoiceIntervalCount++;
+        }
+
+        boolean hasVoice = mVoiceIntervalCount >= MINIMUM_VOICE_INTERVALS;
+
+        if(mCarrierTimedOut && hasVoice)
+        {
+            restoreNoiseFloor();
+            resetCarrierTracking();
+        }
+        else if(mCarrierTimedOut)
+        {
+            addNoisePower(mPower);
+        }
+        else if(mCarrierIntervalCount >= CARRIER_TIMEOUT_INTERVALS && !hasVoice)
+        {
+            //Replace the history so that the carrier takes effect immediately.
+            mCarrierTimedOut = true;
+            mNoiseFloorBeforeCarrier = mNoiseFloor;
+            mNoiseHistoryCount = 0;
+            addNoisePower(mPower);
+        }
+
+        if(mCarrierIntervalCount >= CARRIER_TIMEOUT_INTERVALS)
+        {
+            resetCarrierTracking();
+        }
+    }
+
+    /**
+     * Resets the counts for the current carrier evaluation period.
+     */
+    private void resetCarrierTracking()
+    {
+        mCarrierIntervalCount = 0;
+        mVoiceIntervalCount = 0;
+    }
+
+    /**
+     * Removes a timed out carrier from the noise floor, restoring the noise floor from before the carrier.  If there's
+     * no noise floor from before the carrier, the user threshold is restored until the noise floor can be measured.
+     */
+    private void restoreNoiseFloor()
+    {
+        mCarrierTimedOut = false;
+        mNoiseHistoryCount = 0;
+
+        if(mNoiseFloorBeforeCarrier != null)
+        {
+            addNoisePower(mNoiseFloorBeforeCarrier);
+            mNoiseFloorBeforeCarrier = null;
+        }
+        else
+        {
+            mNoiseFloor = null;
+            mLowestNoiseFloor = null;
+            applySquelchThreshold(mUserThreshold);
+        }
+    }
+
+    /**
+     * Adds the power to the noise history.
+     * @param power of the interval
+     */
+    private void addNoisePower(float power)
+    {
+        mNoiseHistory[mNoiseHistoryPointer] = power;
+        mNoiseHistoryPointer = (mNoiseHistoryPointer + 1) % NOISE_WINDOW_INTERVALS;
+        mNoiseHistoryCount = Math.min(mNoiseHistoryCount + 1, NOISE_WINDOW_INTERVALS);
+    }
+
+    /**
+     * Sets the squelch threshold to the margin over the current noise floor, where the margin is the larger of the
+     * minimum margin and the amount that the user threshold exceeds the lowest observed noise floor.
+     */
+    private void updateTrackedThreshold()
+    {
+        float noiseFloor = Float.MAX_VALUE;
+
+        for(int x = 0; x < mNoiseHistoryCount; x++)
+        {
+            int index = (mNoiseHistoryPointer - 1 - x + NOISE_WINDOW_INTERVALS) % NOISE_WINDOW_INTERVALS;
+            noiseFloor = Math.min(noiseFloor, mNoiseHistory[index]);
+        }
+
+        mNoiseFloor = noiseFloor;
+        mLowestNoiseFloor = (mLowestNoiseFloor == null) ? noiseFloor : Math.min(mLowestNoiseFloor, noiseFloor);
+        float threshold = noiseFloor * Math.max(MINIMUM_SQUELCH_MARGIN, mUserThreshold / mLowestNoiseFloor);
+
+        if(threshold != mSquelchThreshold)
+        {
+            applySquelchThreshold(threshold);
         }
     }
 
@@ -255,6 +471,15 @@ public class AdaptiveSquelch implements Listener<SourceEvent>
         return !mSquelch;
     }
 
+    /**
+     * Indicates if audio should be passed.  This is false during the hang period, while the signal is below the close
+     * threshold but the squelch is still open.
+     */
+    public boolean isAudioEnabled()
+    {
+        return !mSquelch && mHangCount == 0;
+    }
+
     /**
      * Current power level
      * @return current power level in dB
@@ -309,6 +534,7 @@ public class AdaptiveSquelch implements Listener<SourceEvent>
         {
             case REQUEST_CHANGE_SQUELCH_THRESHOLD:
                 setSquelchThreshold(sourceEvent.getValue().floatValue());
+                broadcast(SourceEvent.squelchUserThreshold(toDb(mUserThreshold)));
                 break;
             case REQUEST_CURRENT_SQUELCH_THRESHOLD:
                 broadcast(SourceEvent.squelchThreshold(null, getSquelchThreshold()));

src/main/java/io/github/dsheirer/dsp/squelch/NoiseSquelch.java

@@ -1,6 +1,6 @@
 /*
  * *****************************************************************************
- * Copyright (C) 2014-2025 Dennis Sheirer
+ * Copyright (C) 2014-2026 Dennis Sheirer
  *
  * This program is free software: you can redistribute it and/or modify
  * it under the terms of the GNU General Public License as published by
@@ -23,9 +23,11 @@ import io.github.dsheirer.audio.squelch.SquelchState;
 import io.github.dsheirer.dsp.filter.FilterFactory;
 import io.github.dsheirer.dsp.filter.fir.real.IRealFilter;
 import io.github.dsheirer.dsp.filter.fir.real.RealFIRFilter;
+import io.github.dsheirer.dsp.fm.ScalarFMDemodulator;
 import io.github.dsheirer.dsp.window.WindowType;
 import io.github.dsheirer.sample.Listener;
 import java.util.Arrays;
+import java.util.Random;
 
 /**
  * Squelch processor for unfiltered, demodulated audio that operators by high-pass filtering the audio to remove below
@@ -47,6 +49,12 @@ public class NoiseSquelch implements INoiseSquelchController
     public static final float DEFAULT_NOISE_CLOSE_THRESHOLD = 0.19f;
     public static final float MINIMUM_NOISE_THRESHOLD = 0.1f;
     public static final float MAXIMUM_NOISE_THRESHOLD = 0.5f;
+    private static final int HIGH_PASS_FILTER_CUTOFF = 3000;
+    private static final int HIGH_PASS_FILTER_LENGTH = 31;
+    //Noise-only variance of a 12.5 kHz channel at 25 kHz, which is the reference that the noise thresholds are set against.
+    private static final float REFERENCE_NOISE_VARIANCE = 0.298f;
+    private static final int NOISE_MEASUREMENT_SETTLING_SAMPLES = 512;
+    private static final long NOISE_MEASUREMENT_SEED = 1L;
     private float[] mFilteredBuffer = new float[0];
     private float[] mAudioBuffer = new float[0];
     private float mMeanAccumulator;
@@ -227,7 +235,7 @@ public class NoiseSquelch implements INoiseSquelchController
      */
     public void setSampleRate(double sampleRate)
     {
-        float[] coefficients = FilterFactory.getHighPass((int)sampleRate, 3000, 31, WindowType.BLACKMAN_HARRIS_7);
+        float[] coefficients = getHighPassCoefficients(sampleRate);
         mHighPassFilter = new RealFIRFilter(coefficients);
         mVarianceWindowSize = (int)(sampleRate * (VARIANCE_CALCULATION_WINDOW_MILLISECONDS / 1000.0));
 
@@ -235,6 +243,88 @@ public class NoiseSquelch implements INoiseSquelchController
         mAudioBufferFilterDelay = (int)Math.ceil(coefficients.length / 2.0);
     }
 
+    /**
+     * Sets the sample rate for the incoming demodulated audio sample stream and normalizes the noise measurement for
+     * the channel filter applied ahead of the FM demodulator.  The demodulated noise variance depends on the ratio of
+     * the channel bandwidth to the sample rate and, without normalization, a narrow channel can have a noise-only
+     * variance that is below the noise close threshold, which holds the squelch open.  The noise measurement is scaled
+     * up so that a noise-only channel measures at the reference noise variance.  The noise measurement is never scaled
+     * down, so channels that are already above the reference are unchanged.
+     *
+     * @param sampleRate of the sample stream.
+     * @param channelFilter coefficients of the low-pass channel filter applied ahead of the FM demodulator.
+     */
+    public void setSampleRate(double sampleRate, float[] channelFilter)
+    {
+        setSampleRate(sampleRate);
+
+        float gain = (float)Math.sqrt(Math.max(1.0f, REFERENCE_NOISE_VARIANCE / getNoiseVariance(sampleRate, channelFilter)));
+        float[] coefficients = getHighPassCoefficients(sampleRate);
+
+        for(int x = 0; x < coefficients.length; x++)
+        {
+            coefficients[x] *= gain;
+        }
+
+        mHighPassFilter = new RealFIRFilter(coefficients);
+    }
+
+    /**
+     * Creates the high-pass filter that isolates the noise in the demodulated audio.
+     * @param sampleRate of the demodulated audio.
+     * @return filter coefficients
+     */
+    private static float[] getHighPassCoefficients(double sampleRate)
+    {
+        return FilterFactory.getHighPass((int)sampleRate, HIGH_PASS_FILTER_CUTOFF, HIGH_PASS_FILTER_LENGTH,
+                WindowType.BLACKMAN_HARRIS_7);
+    }
+
+    /**
+     * Measures the variance that the squelch sees when the channel contains only noise, using one second of a
+     * repeatable sequence of complex noise samples.
+     *
+     * @param sampleRate of the channel.
+     * @param channelFilter coefficients of the low-pass channel filter applied ahead of the FM demodulator.
+     * @return noise-only variance of the demodulated, high-pass filtered samples.
+     */
+    public static float getNoiseVariance(double sampleRate, float[] channelFilter)
+    {
+        int length = (int)sampleRate;
+        float[] i = new float[length];
+        float[] q = new float[length];
+        Random random = new Random(NOISE_MEASUREMENT_SEED);
+
+        for(int x = 0; x < length; x++)
+        {
+            i[x] = (float)random.nextGaussian();
+            q[x] = (float)random.nextGaussian();
+        }
+
+        float[] demodulated = new ScalarFMDemodulator().demodulate(new RealFIRFilter(channelFilter.clone()).filter(i),
+                new RealFIRFilter(channelFilter.clone()).filter(q));
+        float[] noise = new RealFIRFilter(getHighPassCoefficients(sampleRate)).filter(demodulated);
+
+        int count = length - NOISE_MEASUREMENT_SETTLING_SAMPLES;
+        double mean = 0.0;
+
+        for(int x = NOISE_MEASUREMENT_SETTLING_SAMPLES; x < length; x++)
+        {
+            mean += noise[x];
+        }
+
+        mean /= count;
+
+        double variance = 0.0;
+
+        for(int x = NOISE_MEASUREMENT_SETTLING_SAMPLES; x < length; x++)
+        {
+            variance += (noise[x] - mean) * (noise[x] - mean);
+        }
+
+        return (float)(variance / count);
+    }
+
     public void process(float[] samples)
     {
         float[] filtered = mHighPassFilter.filter(samples);

src/main/java/io/github/dsheirer/dsp/squelch/VoiceModulationDetector.java

@@ -0,0 +1,158 @@
+/*
+ * *****************************************************************************
+ * Copyright (C) 2014-2026 Dennis Sheirer
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program.  If not, see <http://www.gnu.org/licenses/>
+ * ****************************************************************************
+ */
+package io.github.dsheirer.dsp.squelch;
+
+import org.jtransforms.fft.FloatFFT_1D;
+
+/**
+ * Detects voice modulation on the envelope of a steady AM carrier.  The noise on a carrier's envelope is spectrally flat
+ * across the channel, while voice energy is concentrated in the lower part of the voice band.  The detector compares
+ * the average spectral density of a low and a high band, with band edges limited to the channel pass band.
+ *
+ * A single detection isn't proof of a voice transmission and a pause in speech isn't proof of a dead carrier, so the
+ * results should be evaluated across a longer period.
+ */
+public class VoiceModulationDetector
+{
+    private static final float MAXIMUM_FREQUENCY = 2300.0f;
+    private static final float MAXIMUM_FREQUENCY_BANDWIDTH_RATIO = 0.38f;
+    private static final float LOW_BAND_START = 300.0f;
+    private static final float LOW_BAND_STOP_RATIO = 0.52f;
+    private static final float HIGH_BAND_START_RATIO = 0.65f;
+    private static final double DETECTION_THRESHOLD_DB = 5.0;
+
+    private final double mBandwidth;
+    private FloatFFT_1D mFFT;
+    private float[] mEnvelope;
+    private float[] mWindow;
+    private int mLowStartBin;
+    private int mLowStopBin;
+    private int mHighStartBin;
+    private int mHighStopBin;
+    private int mPointer = 0;
+
+    /**
+     * Constructs an instance
+     * @param sampleRate of the envelope samples in hertz
+     * @param bandwidth of the channel in hertz, spanning positive and negative frequencies
+     * @param analysisSamples maximum number of samples per analysis.  This is reduced to a power of 2.
+     */
+    public VoiceModulationDetector(double sampleRate, double bandwidth, int analysisSamples)
+    {
+        mBandwidth = bandwidth;
+        configure(sampleRate, analysisSamples);
+    }
+
+    /**
+     * Updates the sample rate and resets this detector.
+     * @param sampleRate of the envelope samples in hertz
+     * @param analysisSamples maximum number of samples per analysis.  This is reduced to a power of 2.
+     */
+    public final void configure(double sampleRate, int analysisSamples)
+    {
+        int length = Integer.highestOneBit(analysisSamples);
+        mFFT = new FloatFFT_1D(length);
+        mEnvelope = new float[length];
+        mWindow = new float[length];
+
+        for(int x = 0; x < length; x++)
+        {
+            mWindow[x] = (float)(0.5 - 0.5 * Math.cos(2.0 * Math.PI * x / length));
+        }
+
+        float stop = Math.min(MAXIMUM_FREQUENCY, (float)mBandwidth * MAXIMUM_FREQUENCY_BANDWIDTH_RATIO);
+        double hertzPerBin = sampleRate / length;
+        mLowStartBin = (int)Math.ceil(LOW_BAND_START / hertzPerBin);
+        mLowStopBin = (int)(stop * LOW_BAND_STOP_RATIO / hertzPerBin);
+        mHighStartBin = (int)Math.ceil(stop * HIGH_BAND_START_RATIO / hertzPerBin);
+        mHighStopBin = (int)(stop / hertzPerBin);
+        reset();
+    }
+
+    /**
+     * Discards any partial analysis buffer.
+     */
+    public void reset()
+    {
+        mPointer = 0;
+    }
+
+    /**
+     * Adds an envelope sample to the analysis buffer.  Samples are ignored once the buffer is full.
+     * @param envelope sample
+     */
+    public void receive(float envelope)
+    {
+        if(mPointer < mEnvelope.length)
+        {
+            mEnvelope[mPointer++] = envelope;
+        }
+    }
+
+    /**
+     * Analyzes the buffered samples and resets this detector.
+     * @return true if the analysis buffer is full and the samples contain voice modulation.
+     */
+    public boolean analyze()
+    {
+        boolean full = mPointer == mEnvelope.length;
+        mPointer = 0;
+
+        if(!full)
+        {
+            return false;
+        }
+
+        float mean = 0.0f;
+
+        for(float sample: mEnvelope)
+        {
+            mean += sample;
+        }
+
+        mean /= mEnvelope.length;
+
+        for(int x = 0; x < mEnvelope.length; x++)
+        {
+            mEnvelope[x] = (mEnvelope[x] - mean) * mWindow[x];
+        }
+
+        mFFT.realForward(mEnvelope);
+        double low = getBandPower(mLowStartBin, mLowStopBin);
+        double high = getBandPower(mHighStartBin, mHighStopBin);
+        return high > 0.0 && 10.0 * Math.log10(low / high) >= DETECTION_THRESHOLD_DB;
+    }
+
+    /**
+     * Calculates the mean power of the bins from the real transform output of interleaved real and imaginary values.
+     */
+    private double getBandPower(int startBin, int stopBin)
+    {
+        double power = 0.0;
+
+        for(int bin = startBin; bin < stopBin; bin++)
+        {
+            double real = mEnvelope[2 * bin];
+            double imaginary = mEnvelope[2 * bin + 1];
+            power += real * real + imaginary * imaginary;
+        }
+
+        return power / Math.max(1, stopBin - startBin);
+    }
+}

src/main/java/io/github/dsheirer/gui/playlist/channel/AMConfigurationEditor.java

@@ -301,7 +301,7 @@ public class AMConfigurationEditor extends ChannelConfigurationEditor
                         DecodeConfigAM.Bandwidth bandwidth = config.getBandwidth();
                         if(bandwidth == null)
                         {
-                            bandwidth = DecodeConfigNBFM.Bandwidth.BW_15_0;
+                            bandwidth = DecodeConfigAM.DEFAULT_BANDWIDTH;
                         }
 
                         for(Toggle toggle: getBandwidthButton().getToggleGroup().getToggles())
@@ -409,7 +409,7 @@ public class AMConfigurationEditor extends ChannelConfigurationEditor
         {
             getBandwidthButton().setDisable(false);
             final DecodeConfigAM.Bandwidth bandwidth = (decodeConfigAM.getBandwidth() != null ?
-                    decodeConfigAM.getBandwidth() : DecodeConfigNBFM.Bandwidth.BW_15_0);
+                    decodeConfigAM.getBandwidth() : DecodeConfigAM.DEFAULT_BANDWIDTH);
 
             for(Toggle toggle: getBandwidthButton().getToggleGroup().getToggles())
             {
@@ -454,7 +454,7 @@ public class AMConfigurationEditor extends ChannelConfigurationEditor
             config = new DecodeConfigAM();
         }
 
-        DecodeConfigAM.Bandwidth bandwidth = DecodeConfigAM.Bandwidth.BW_15_0;
+        DecodeConfigAM.Bandwidth bandwidth = DecodeConfigAM.DEFAULT_BANDWIDTH;
 
         if(getBandwidthButton().getToggleGroup().getSelectedToggle() != null)
         {

src/main/java/io/github/dsheirer/gui/power/SignalPowerView.java

@@ -109,6 +109,7 @@ public class SignalPowerView extends JPanel
         mSquelchAutoTrackCheckBox.addActionListener(e ->
         {
             broadcast(SourceEvent.requestSquelchAutoTrack(mSquelchAutoTrackCheckBox.isSelected()));
+            setConfigSquelchAutoTrack(mSquelchAutoTrackCheckBox.isSelected());
         });
         valuePanel.add(mSquelchAutoTrackCheckBox, "span,left");
 
@@ -116,7 +117,11 @@ public class SignalPowerView extends JPanel
     }
 
     /**
-     * Updates the channel's decode configuration with a new squelch threshold value
+     * Updates the channel's decode configuration with a new squelch threshold value.
+     *
+     * Note: this is only used for the user threshold notification that follows a user change.  The threshold
+     * notifications from the decoder can be values that are automatically tracked from current channel conditions, and
+     * saving those would replace the user's setting.
      */
     private void setConfigSquelchThreshold(int threshold)
     {
@@ -195,7 +200,6 @@ public class SignalPowerView extends JPanel
             {
                 final double threshold = sourceEvent.getValue().doubleValue();
                 mSquelchThreshold = threshold;
-                setConfigSquelchThreshold((int)threshold);
 
                 EventQueue.invokeLater(() -> {
                     mPowerMeter.setSquelchThreshold(threshold);
@@ -206,10 +210,11 @@ public class SignalPowerView extends JPanel
                     mSquelchUpButton.setEnabled(true);
                 });
             }
+            case NOTIFICATION_SQUELCH_USER_THRESHOLD ->
+                    setConfigSquelchThreshold((int)Math.round(sourceEvent.getValue().doubleValue()));
             case NOTIFICATION_SQUELCH_AUTO_TRACK ->
             {
                 boolean autoTrack = sourceEvent.getValue().intValue() == 1;
-                setConfigSquelchAutoTrack(autoTrack);
                 EventQueue.invokeLater(() -> {
                     mSquelchAutoTrackCheckBox.setSelected(autoTrack);
                     mSquelchAutoTrackCheckBox.setEnabled(true);
@@ -225,5 +230,9 @@ public class SignalPowerView extends JPanel
     {
         mProcessingChain = processingChain;
         reset();
+
+        //Request the current squelch settings, which enables the squelch controls when the decoder responds.
+        broadcast(SourceEvent.requestCurrentSquelchThreshold());
+        broadcast(SourceEvent.requestCurrentSquelchAutoTrack());
     }
 }

src/main/java/io/github/dsheirer/gui/preference/application/AppearancePreferenceEditor.java

@@ -25,6 +25,7 @@ import io.github.dsheirer.preference.application.ApplicationPreference;
 import javafx.geometry.Insets;
 import javafx.geometry.Orientation;
 import javafx.scene.control.Button;
+import javafx.scene.control.CheckBox;
 import javafx.scene.control.Label;
 import javafx.scene.control.RadioButton;
 import javafx.scene.control.Separator;
@@ -45,6 +46,7 @@ public class AppearancePreferenceEditor extends HBox
     private final ApplicationPreference mApplicationPreference;
     private GridPane mEditorPane;
     private VBox mThemeRadioGroup;
+    private CheckBox mComplementaryAliasColorsCheckBox;
     private Slider mGuiScaleSlider;
     private Label mGuiScaleValueLabel;
 
@@ -74,6 +76,12 @@ public class AppearancePreferenceEditor extends HBox
 
             mEditorPane.add(new Label("Theme"), 0, row, 3, 1);
             mEditorPane.add(getThemeRadioGroup(), 0, ++row, 3, 1);
+            mEditorPane.add(getComplementaryAliasColorsCheckBox(), 0, ++row, 3, 1);
+
+            Label aliasColorHint = new Label("Dark themes only. Replaces alias colors that are hard to read against " +
+                "the background with a complementary color.");
+            aliasColorHint.setWrapText(true);
+            mEditorPane.add(aliasColorHint, 0, ++row, 3, 1);
 
             Separator separator = new Separator(Orientation.HORIZONTAL);
             GridPane.setHgrow(separator, Priority.ALWAYS);
@@ -139,6 +147,22 @@ public class AppearancePreferenceEditor extends HBox
         return mThemeRadioGroup;
     }
 
+    /**
+     * Check box to opt in to replacing hard to read alias colors with a complementary color in dark themes.
+     */
+    private CheckBox getComplementaryAliasColorsCheckBox()
+    {
+        if(mComplementaryAliasColorsCheckBox == null)
+        {
+            mComplementaryAliasColorsCheckBox = new CheckBox("Use Complementary Alias Colors");
+            mComplementaryAliasColorsCheckBox.setSelected(mApplicationPreference.isComplementaryAliasColors());
+            mComplementaryAliasColorsCheckBox.setOnAction(e -> mApplicationPreference
+                .setComplementaryAliasColors(mComplementaryAliasColorsCheckBox.isSelected()));
+        }
+
+        return mComplementaryAliasColorsCheckBox;
+    }
+
     /**
      * Slider to adjust the global GUI zoom factor.  The slider snaps to 10% increments and only
      * persists the value when the user releases the slider so we do not thrash a LAF reinstall on

src/main/java/io/github/dsheirer/gui/theme/ThemeManager.java

@@ -74,6 +74,7 @@ public class ThemeManager
     private volatile UserPreferences mUserPreferences;
     private volatile Theme mCurrentTheme = Theme.LIGHT;
     private volatile double mCurrentGuiScale = 1.0d;
+    private volatile boolean mComplementaryAliasColors = false;
     /** Data URL of the currently-active per-theme accent stylesheet, or null. */
     private volatile String mAccentStylesheetUrl;
 
@@ -109,6 +110,7 @@ public class ThemeManager
         mUserPreferences = userPreferences;
         mCurrentTheme = userPreferences.getApplicationPreference().getTheme();
         mCurrentGuiScale = userPreferences.getApplicationPreference().getGuiScale();
+        mComplementaryAliasColors = userPreferences.getApplicationPreference().isComplementaryAliasColors();
 
         if(firstBind)
         {
@@ -225,12 +227,12 @@ public class ThemeManager
      * Provides the color to render user-selected content (e.g. an alias) against a background in the current theme.
      * @param color selected by the user.
      * @param background that the color is rendered against.
-     * @return the color, or a readable alternative when dark mode is active and the color lacks contrast with the
-     * background.
+     * @return the color, or a readable alternative when the user enabled complementary alias colors, dark mode is
+     * active and the color lacks contrast with the background.
      */
     public Color getReadableColor(Color color, Color background)
     {
-        return isDarkMode() ? ColorContrast.getReadable(color, background) : color;
+        return mComplementaryAliasColors && isDarkMode() ? ColorContrast.getReadable(color, background) : color;
     }
 
     public void register(Scene scene)
@@ -288,6 +290,20 @@ public class ThemeManager
 
         Theme updated = mUserPreferences.getApplicationPreference().getTheme();
         double updatedScale = mUserPreferences.getApplicationPreference().getGuiScale();
+        boolean updatedComplementary = mUserPreferences.getApplicationPreference().isComplementaryAliasColors();
+
+        if(updatedComplementary != mComplementaryAliasColors)
+        {
+            mComplementaryAliasColors = updatedComplementary;
+
+            //The Swing table renderers look up the alias color each time they paint.
+            EventQueue.invokeLater(() -> {
+                for(Window window: Window.getWindows())
+                {
+                    window.repaint();
+                }
+            });
+        }
 
         if(updated == mCurrentTheme && Math.abs(updatedScale - mCurrentGuiScale) < 1e-6)
         {

src/main/java/io/github/dsheirer/module/decode/am/AMDecoder.java

@@ -21,20 +21,14 @@ package io.github.dsheirer.module.decode.am;
 import io.github.dsheirer.channel.state.DecoderStateEvent;
 import io.github.dsheirer.channel.state.IDecoderStateEventProvider;
 import io.github.dsheirer.channel.state.State;
+import io.github.dsheirer.dsp.am.ISquelchingDemodulator;
 import io.github.dsheirer.dsp.am.SquelchingAMDemodulator;
+import io.github.dsheirer.dsp.filter.ChannelFilterDesigner;
 import io.github.dsheirer.dsp.filter.FilterFactory;
 import io.github.dsheirer.dsp.filter.decimate.DecimationFilterFactory;
 import io.github.dsheirer.dsp.filter.decimate.IRealDecimationFilter;
-import io.github.dsheirer.dsp.filter.design.FilterDesignException;
-import io.github.dsheirer.dsp.filter.fir.FIRFilterSpecification;
 import io.github.dsheirer.dsp.filter.fir.real.IRealFilter;
 import io.github.dsheirer.dsp.filter.resample.RealResampler;
-import io.github.dsheirer.dsp.fm.ISquelchingDemodulator;
-import io.github.dsheirer.dsp.gain.AudioGainAndDcFilter;
-import io.github.dsheirer.dsp.squelch.INoiseSquelchController;
-import io.github.dsheirer.dsp.squelch.NoiseSquelch;
-import io.github.dsheirer.dsp.squelch.NoiseSquelchState;
-import io.github.dsheirer.dsp.window.WindowType;
 import io.github.dsheirer.module.decode.DecoderType;
 import io.github.dsheirer.module.decode.SquelchControlDecoder;
 import io.github.dsheirer.sample.Listener;
@@ -52,15 +46,9 @@ import org.slf4j.LoggerFactory;
  */
 public class AMDecoder extends SquelchControlDecoder implements ISourceEventListener, ISourceEventProvider,
         IComplexSamplesListener, Listener<ComplexSamples>, IRealBufferProvider,
-        IDecoderStateEventProvider, INoiseSquelchController
+        IDecoderStateEventProvider
 {
     private final static Logger mLog = LoggerFactory.getLogger(AMDecoder.class);
-    private static final float DEMODULATOR_GAIN = 150.0f;
-    private static final float SQUELCH_ALPHA_DECAY = 0.0004f;
-    private static final float MINIMUM_GAIN = 0.5f;
-    private static final float MAXIMUM_GAIN = 16.0f;
-    private static final float OBJECTIVE_AUDIO_AMPLITUDE = 0.75f;
-    private AudioGainAndDcFilter mAGC = new AudioGainAndDcFilter(MINIMUM_GAIN, MAXIMUM_GAIN, OBJECTIVE_AUDIO_AMPLITUDE);
     private static final double DEMODULATED_AUDIO_SAMPLE_RATE = 8000.0;
     private IRealFilter mIBasebandFilter;
     private IRealFilter mQBasebandFilter;
@@ -73,7 +61,6 @@ public class AMDecoder extends SquelchControlDecoder implements ISourceEventList
     private Listener<DecoderStateEvent> mDecoderStateEventListener;
     private final double mChannelBandwidth;
     protected boolean mSquelch = true;
-    private final NoiseSquelch mNoiseSquelch = new NoiseSquelch(0.1f, 0.2f, 4, 6);
 
     /**
      * Constructs an instance
@@ -83,8 +70,8 @@ public class AMDecoder extends SquelchControlDecoder implements ISourceEventList
     public AMDecoder(DecodeConfigAM config)
     {
         super(config);
-        mDemodulator = new SquelchingAMDemodulator(DEMODULATOR_GAIN, SQUELCH_ALPHA_DECAY, config.getSquelchThreshold(),
-                config.isSquelchAutoTrack());
+        mDemodulator = new SquelchingAMDemodulator(config.getSquelchThreshold(), config.isSquelchAutoTrack(),
+                config.getBandwidth().getValue());
 		mChannelBandwidth = config.getBandwidth().getValue();
     }
 
@@ -94,30 +81,6 @@ public class AMDecoder extends SquelchControlDecoder implements ISourceEventList
         return DecoderType.AM;
     }
 
-    @Override
-    public void setSquelchOverride(boolean override)
-    {
-        mNoiseSquelch.setSquelchOverride(override);
-    }
-
-    @Override
-    public void setHysteresisThreshold(int open, int close)
-    {
-        mNoiseSquelch.setHysteresisThreshold(open, close);
-    }
-
-    @Override
-    public void setNoiseThreshold(float open, float close)
-    {
-        mNoiseSquelch.setNoiseThreshold(open, close);
-    }
-
-    @Override
-    public void setNoiseSquelchStateListener(Listener<NoiseSquelchState> listener)
-    {
-        mNoiseSquelch.setNoiseSquelchStateListener(listener);
-    }
-
     /**
      * Implements the ISourceEventListener interface
      */
@@ -154,8 +117,6 @@ public class AMDecoder extends SquelchControlDecoder implements ISourceEventList
         if(mResampledBufferListener != null)
         {
             mResampledBufferListener.receive(demodulatedSamples);
-//            //Apply audio gain and rebroadcast
-//            super.broadcast(mAGC.process(demodulatedSamples));
         }
     }
 
@@ -196,7 +157,7 @@ public class AMDecoder extends SquelchControlDecoder implements ISourceEventList
     {
         if(mIDecimationFilter == null || mQDecimationFilter == null)
         {
-            throw new IllegalStateException("NBFM demodulator module must receive a sample rate change source " +
+            throw new IllegalStateException("AM demodulator module must receive a sample rate change source " +
                     "event before it can process complex sample buffers");
         }
 
@@ -208,8 +169,6 @@ public class AMDecoder extends SquelchControlDecoder implements ISourceEventList
 
         float[] demodulated = mDemodulator.demodulate(filteredI, filteredQ);
 
-        mNoiseSquelch.process(demodulated);
-
         if(mResampler != null)
         {
             //Squelch changed while processing this audio buffer
@@ -225,6 +184,8 @@ public class AMDecoder extends SquelchControlDecoder implements ISourceEventList
                     //Demodulator says to mute and we are unmuted = Squelch and End Call
                     else
                     {
+                        //Process the final audio and flush the resampler so that audio doesn't carry into the next call
+                        mResampler.resample(demodulated, true);
                         mSquelch = true;
                         notifyCallEnd();
                     }
@@ -275,7 +236,6 @@ public class AMDecoder extends SquelchControlDecoder implements ISourceEventList
      */
     protected void notifyCallStart()
     {
-        mAGC.reset();
         broadcast(new DecoderStateEvent(this, DecoderStateEvent.Event.START, State.CALL, 0));
     }
 
@@ -398,53 +358,17 @@ public class AMDecoder extends SquelchControlDecoder implements ISourceEventList
                     mIDecimationFilter = DecimationFilterFactory.getRealDecimationFilter(decimationRate);
                     mQDecimationFilter = DecimationFilterFactory.getRealDecimationFilter(decimationRate);
 
-                    if((decimatedSampleRate < (2.0 * mChannelBandwidth)))
+                    //The complex sample rate must span the two-sided channel bandwidth.
+                    if(decimatedSampleRate < mChannelBandwidth)
                     {
                         throw new IllegalStateException(getDecoderType().name() + " demodulator with channel bandwidth [" +
-                                mChannelBandwidth + "] requires a channel sample rate of [" + (2.0 * mChannelBandwidth +
-                                "] - sample rate of [" + decimatedSampleRate + "] is not supported"));
+                                mChannelBandwidth + "] requires a channel sample rate of at least [" + mChannelBandwidth +
+                                "] - sample rate of [" + decimatedSampleRate + "] is not supported");
                     }
 
                     mDemodulator.setSampleRate((int) decimatedSampleRate);
 
-                    mNoiseSquelch.setSampleRate(decimatedSampleRate);
-
-                    int passBandStop = (int) (mChannelBandwidth * .8);
-                    int stopBandStart = (int) mChannelBandwidth;
-
-                    float[] coefficients = null;
-
-                    FIRFilterSpecification specification = FIRFilterSpecification.lowPassBuilder()
-                            .sampleRate(decimatedSampleRate * 2)
-                            .gridDensity(16)
-                            .oddLength(true)
-                            .passBandCutoff(passBandStop)
-                            .passBandAmplitude(1.0)
-                            .passBandRipple(0.01)
-                            .stopBandStart(stopBandStart)
-                            .stopBandAmplitude(0.0)
-                            .stopBandRipple(0.005) //Approximately 90 dB attenuation
-                            .build();
-
-                    try
-                    {
-                        coefficients = FilterFactory.getTaps(specification);
-                    }
-                    catch(FilterDesignException fde)
-                    {
-                        mLog.error("Couldn't design demodulator remez filter for sample rate [" + sampleRate +
-                                "] pass frequency [" + passBandStop + "] and stop frequency [" + stopBandStart +
-                                "] - will proceed using sinc (low-pass) filter");
-                    }
-
-                    if(coefficients == null)
-                    {
-                        mLog.info("Unable to use remez filter designer for sample rate [" + decimatedSampleRate +
-                                "] pass band stop [" + passBandStop +
-                                "] and stop band start [" + stopBandStart + "] - will proceed using simple low pass filter design");
-                        coefficients = FilterFactory.getLowPass(decimatedSampleRate, passBandStop, stopBandStart, 60,
-                                WindowType.HAMMING, true);
-                    }
+                    float[] coefficients = ChannelFilterDesigner.design(decimatedSampleRate, mChannelBandwidth);
 
                     mIBasebandFilter = FilterFactory.getRealFilter(coefficients);
                     mQBasebandFilter = FilterFactory.getRealFilter(coefficients);

src/main/java/io/github/dsheirer/module/decode/am/DecodeConfigAM.java

@@ -30,6 +30,7 @@ import io.github.dsheirer.source.tuner.channel.ChannelSpecification;
  */
 public class DecodeConfigAM extends DecodeConfigAnalog implements ISquelchConfiguration
 {
+    public static final Bandwidth DEFAULT_BANDWIDTH = Bandwidth.BW_6_0;
     private int mSquelchThreshold = -78;
     private boolean mSquelchAutoTrack = true;
 
@@ -46,7 +47,7 @@ public class DecodeConfigAM extends DecodeConfigAnalog implements ISquelchConfig
     @Override
     protected Bandwidth getDefaultBandwidth()
     {
-        return Bandwidth.BW_15_0;
+        return DEFAULT_BANDWIDTH;
     }
 
     /**
@@ -62,12 +63,14 @@ public class DecodeConfigAM extends DecodeConfigAnalog implements ISquelchConfig
                 return new ChannelSpecification(25000.0, 3000, 1500.0, 1700.0);
             case BW_5_0:
                 return new ChannelSpecification(25000.0, 5000, 2500.0, 2700.0);
+            case BW_6_0:
+                return new ChannelSpecification(25000.0, 6000, 3000.0, 3200.0);
             case BW_8_33:
                 return new ChannelSpecification(25000.0, 10000, 5000.0, 7000.0);
             case BW_15_0:
-                return new ChannelSpecification(25000.0, 15000, 7500.0, 9500.0);
+                return new ChannelSpecification(30000.0, 15000, 7500.0, 9500.0);
             case BW_25_0:
-                return new ChannelSpecification(25000.0, 25000, 12500.0, 14500.0);
+                return new ChannelSpecification(50000.0, 25000, 12500.0, 14500.0);
             default:
                 throw new IllegalArgumentException("Unrecognized AM bandwidth value: " + getBandwidth());
         }

src/main/java/io/github/dsheirer/module/decode/analog/DecodeConfigAnalog.java

@@ -100,6 +100,7 @@ public abstract class DecodeConfigAnalog extends DecodeConfiguration
     {
         BW_3_0("3.0 kHz", 3000.0),
         BW_5_0("5.0 kHz", 5000.0),
+        BW_6_0("6.0 kHz", 6000.0),
         BW_7_5("7.5 kHz", 7500.0),
         BW_8_33("8.33 kHz", 8333.0),
         BW_12_5("12.5 kHz", 12500.0),
@@ -121,7 +122,7 @@ public abstract class DecodeConfigAnalog extends DecodeConfiguration
         }
 
         //AM demodulator channel bandwidth options
-        public static EnumSet<Bandwidth> AM_BANDWIDTHS = EnumSet.of(BW_3_0, BW_5_0, BW_8_33, BW_15_0, BW_25_0);
+        public static EnumSet<Bandwidth> AM_BANDWIDTHS = EnumSet.of(BW_3_0, BW_5_0, BW_6_0, BW_8_33, BW_15_0, BW_25_0);
 
         //FM demodulator channel bandwidth options
         public static EnumSet<Bandwidth> FM_BANDWIDTHS = EnumSet.of(BW_7_5, BW_12_5, BW_25_0);

src/main/java/io/github/dsheirer/module/decode/nbfm/NBFMDecoder.java

@@ -22,11 +22,10 @@ import io.github.dsheirer.audio.squelch.SquelchState;
 import io.github.dsheirer.channel.state.DecoderStateEvent;
 import io.github.dsheirer.channel.state.IDecoderStateEventProvider;
 import io.github.dsheirer.channel.state.State;
+import io.github.dsheirer.dsp.filter.ChannelFilterDesigner;
 import io.github.dsheirer.dsp.filter.FilterFactory;
 import io.github.dsheirer.dsp.filter.decimate.DecimationFilterFactory;
 import io.github.dsheirer.dsp.filter.decimate.IRealDecimationFilter;
-import io.github.dsheirer.dsp.filter.design.FilterDesignException;
-import io.github.dsheirer.dsp.filter.fir.FIRFilterSpecification;
 import io.github.dsheirer.dsp.filter.fir.real.IRealFilter;
 import io.github.dsheirer.dsp.filter.resample.RealResampler;
 import io.github.dsheirer.dsp.fm.FmDemodulatorFactory;
@@ -34,7 +33,6 @@ import io.github.dsheirer.dsp.fm.IDemodulator;
 import io.github.dsheirer.dsp.squelch.INoiseSquelchController;
 import io.github.dsheirer.dsp.squelch.NoiseSquelch;
 import io.github.dsheirer.dsp.squelch.NoiseSquelchState;
-import io.github.dsheirer.dsp.window.WindowType;
 import io.github.dsheirer.module.decode.DecoderType;
 import io.github.dsheirer.module.decode.SquelchControlDecoder;
 import io.github.dsheirer.module.decode.squelch.SquelchCodeState;
@@ -454,39 +452,9 @@ public class NBFMDecoder extends SquelchControlDecoder implements ISourceEventLi
             throw new IllegalStateException(getDecoderType().name() + " demodulator with channel bandwidth [" + mChannelBandwidth + "] requires a channel sample rate of [" + (2.0 * mChannelBandwidth + "] - sample rate of [" + decimatedSampleRate + "] is not supported"));
         }
 
-        mNoiseSquelch.setSampleRate(decimatedSampleRate);
+        float[] coefficients = ChannelFilterDesigner.design(decimatedSampleRate, mChannelBandwidth);
 
-        int passBandStop = (int) (mChannelBandwidth * .8);
-        int stopBandStart = (int) mChannelBandwidth;
-
-        float[] coefficients = null;
-
-        FIRFilterSpecification specification = FIRFilterSpecification.lowPassBuilder()
-                .sampleRate(decimatedSampleRate * 2)
-                .gridDensity(16)
-                .oddLength(true)
-                .passBandCutoff(passBandStop)
-                .passBandAmplitude(1.0)
-                .passBandRipple(0.01)
-                .stopBandStart(stopBandStart)
-                .stopBandAmplitude(0.0)
-                .stopBandRipple(0.005)
-                .build();
-
-        try
-        {
-            coefficients = FilterFactory.getTaps(specification);
-        }
-        catch(FilterDesignException fde)
-        {
-            mLog.error("Couldn't design demodulator remez filter for sample rate [" + sampleRate + "] pass frequency [" + passBandStop + "] and stop frequency [" + stopBandStart + "] - will proceed using sinc (low-pass) filter");
-        }
-
-        if(coefficients == null)
-        {
-            mLog.info("Unable to use remez filter designer for sample rate [" + decimatedSampleRate + "] pass band stop [" + passBandStop + "] and stop band start [" + stopBandStart + "] - will proceed using simple low pass filter design");
-            coefficients = FilterFactory.getLowPass(decimatedSampleRate, passBandStop, stopBandStart, 60, WindowType.HAMMING, true);
-        }
+        mNoiseSquelch.setSampleRate(decimatedSampleRate, coefficients);
 
         mIBasebandFilter = FilterFactory.getRealFilter(coefficients);
         mQBasebandFilter = FilterFactory.getRealFilter(coefficients);

src/main/java/io/github/dsheirer/module/decode/p25/phase1/P25P1MessageFramer.java

@@ -796,6 +796,10 @@ public class P25P1MessageFramer extends C4FMMessageFramer
                 {
                     dispatchMessage();
                 }
+                else
+                {
+                    mMessageAssembler = null;
+                }
             }
             else
             {
@@ -803,6 +807,18 @@ public class P25P1MessageFramer extends C4FMMessageFramer
                 dispatchDroppedSamples(droppedBitCount);
                 dispatchMessage();
             }
+
+            //A multi-block TSBK or PDU reconfigures the assembler for its next block.  A place holder that resolved to
+            //a PDU may already contain those blocks, so dispatch each block that's fully assembled.
+            while(mMessageAssembler != null && mMessageAssembler.isComplete())
+            {
+                dispatchMessage();
+            }
+
+            //The new NID ended the multi-block sequence, so the assembler can't continue into the next frame, which
+            //would prevent starting the assembler for that frame.  The elapsed dibits are reported as sync loss.
+            mMessageAssembler = null;
+            mPDUSequence = null;
         }
 
         mDibitCounter -= 57;

src/main/java/io/github/dsheirer/preference/application/ApplicationPreference.java

@@ -37,6 +37,7 @@ public class ApplicationPreference extends Preference
     private static final String PREFERENCE_KEY_DARK_MODE = "dark.mode";
     private static final String PREFERENCE_KEY_THEME = "ui.theme";
     private static final String PREFERENCE_KEY_GUI_SCALE = "ui.gui.scale";
+    private static final String PREFERENCE_KEY_COMPLEMENTARY_ALIAS_COLORS = "ui.complementary.alias.colors";
 
     /** Hard bounds for the GUI zoom factor. */
     public static final double MIN_GUI_SCALE = 0.5d;
@@ -49,6 +50,7 @@ public class ApplicationPreference extends Preference
     private Boolean mAutomaticDiagnosticMonitoring;
     private Theme mTheme;
     private Double mGuiScale;
+    private Boolean mComplementaryAliasColors;
 
     /**
      * Constructs an instance
@@ -167,6 +169,32 @@ public class ApplicationPreference extends Preference
         return getTheme().isDark();
     }
 
+    /**
+     * Indicates if alias colors that lack contrast with the background are replaced with a complementary color when a
+     * dark theme is active.
+     * @return true if enabled.  Default is false, so that aliases display the color selected by the user.
+     */
+    public boolean isComplementaryAliasColors()
+    {
+        if(mComplementaryAliasColors == null)
+        {
+            mComplementaryAliasColors = mPreferences.getBoolean(PREFERENCE_KEY_COMPLEMENTARY_ALIAS_COLORS, false);
+        }
+
+        return mComplementaryAliasColors;
+    }
+
+    /**
+     * Sets the enabled state for using complementary alias colors in dark themes.
+     * @param enabled true to replace alias colors that lack contrast with the background.
+     */
+    public void setComplementaryAliasColors(boolean enabled)
+    {
+        mComplementaryAliasColors = enabled;
+        mPreferences.putBoolean(PREFERENCE_KEY_COMPLEMENTARY_ALIAS_COLORS, enabled);
+        notifyPreferenceUpdated();
+    }
+
     /**
      * Returns the GUI zoom factor.  1.0 = 100% (default).  Bounded to
      * [{@link #MIN_GUI_SCALE}, {@link #MAX_GUI_SCALE}].

src/main/java/io/github/dsheirer/source/SourceEvent.java

@@ -45,6 +45,7 @@ public class SourceEvent
         NOTIFICATION_RECORDING_FILE_LOADED,
         NOTIFICATION_SAMPLE_RATE_CHANGE,
         NOTIFICATION_SQUELCH_THRESHOLD,
+        NOTIFICATION_SQUELCH_USER_THRESHOLD,
         NOTIFICATION_SQUELCH_AUTO_TRACK,
         NOTIFICATION_STOP_SAMPLE_STREAM,
         NOTIFICATION_TUNER_SHUTDOWN,
@@ -428,6 +429,17 @@ public class SourceEvent
         return new SourceEvent(Event.NOTIFICATION_SQUELCH_THRESHOLD, source, thresholdDb);
     }
 
+    /**
+     * Creates a new squelch user threshold notification, which is the setting to save after a user change request.  This
+     * can differ from the current squelch threshold when auto-tracking the noise floor.
+     * @param thresholdDb setting
+     * @return new source event
+     */
+    public static SourceEvent squelchUserThreshold(double thresholdDb)
+    {
+        return new SourceEvent(Event.NOTIFICATION_SQUELCH_USER_THRESHOLD, null, thresholdDb);
+    }
+
     /**
      * Requests the current squelch threshold value
      * @return source event

src/main/java/io/github/dsheirer/source/tuner/channel/TunerChannelSource.java

@@ -204,6 +204,7 @@ public abstract class TunerChannelSource extends ComplexSource implements ISourc
             case NOTIFICATION_FREQUENCY_ROTATION_SUCCESS:
             case NOTIFICATION_CHANNEL_POWER:
             case NOTIFICATION_SQUELCH_THRESHOLD:
+            case NOTIFICATION_SQUELCH_USER_THRESHOLD:
             case NOTIFICATION_SQUELCH_AUTO_TRACK:
             case REQUEST_CHANGE_SQUELCH_THRESHOLD:
             case REQUEST_CURRENT_SQUELCH_THRESHOLD:

src/main/java/org/jtransforms/fft/ReusableFloatInverseFFT.java

@@ -0,0 +1,156 @@
+/*
+ * *****************************************************************************
+ * Copyright (C) 2014-2026 Dennis Sheirer
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program.  If not, see <http://www.gnu.org/licenses/>
+ * ****************************************************************************
+ */
+package org.jtransforms.fft;
+
+import java.util.ArrayList;
+import java.util.List;
+
+/**
+ * Scaled complex inverse FFT that produces the same values as FloatFFT_1D.complexInverse(samples, offset, true) without
+ * allocating on each call.
+ *
+ * FloatFFT_1D allocates a scratch array of two floats per channel on every mixed-radix transform.  This class runs the
+ * same mixed-radix passes using a single reused scratch array.  It's in this package because those passes are package
+ * private.  Sizes that FloatFFT_1D doesn't transform as mixed-radix (powers of two and sizes with other prime factors)
+ * are delegated to FloatFFT_1D.
+ *
+ * Note: this class isn't thread safe because the scratch array is shared across calls.
+ */
+public class ReusableFloatInverseFFT
+{
+    private static final int[] SUPPORTED_RADIX = {3, 5};
+    private final FloatFFT_1D mFFT;
+    private final int mSize;
+    private final int[] mFactors;
+    private final float[] mScratch;
+    private final float mScale;
+
+    /**
+     * Constructs an instance
+     * @param size of the transform in complex samples
+     */
+    public ReusableFloatInverseFFT(int size)
+    {
+        mSize = size;
+        mFFT = new FloatFFT_1D(size);
+        mFactors = getFactors(size);
+        mScratch = mFactors != null ? new float[2 * size] : null;
+        mScale = 1.0f / size;
+    }
+
+    /**
+     * Identifies the order of radix passes for the size, matching the order used by FloatFFT_1D.
+     * @param size of the transform
+     * @return radix values in pass order, or null if the size should be delegated to FloatFFT_1D.
+     */
+    private static int[] getFactors(int size)
+    {
+        if(size < 2 || Integer.bitCount(size) == 1)
+        {
+            return null;
+        }
+
+        List<Integer> factors = new ArrayList<>();
+        int remaining = size;
+
+        while(remaining % 4 == 0)
+        {
+            factors.add(4);
+            remaining /= 4;
+        }
+
+        //FloatFFT_1D moves a radix-2 pass to the front
+        if(remaining % 2 == 0)
+        {
+            factors.addFirst(2);
+            remaining /= 2;
+        }
+
+        for(int radix : SUPPORTED_RADIX)
+        {
+            while(remaining % radix == 0)
+            {
+                factors.add(radix);
+                remaining /= radix;
+            }
+        }
+
+        if(remaining != 1)
+        {
+            return null;
+        }
+
+        return factors.stream().mapToInt(Integer::intValue).toArray();
+    }
+
+    /**
+     * Performs a scaled inverse transform in place.
+     * @param samples containing interleaved I/Q values
+     * @param offset to the start of the block in the samples array
+     */
+    public void complexInverse(float[] samples, int offset)
+    {
+        if(mFactors == null)
+        {
+            mFFT.complexInverse(samples, offset, true);
+            return;
+        }
+
+        final float[] scratch = mScratch;
+        final int size = mSize;
+        boolean resultsInScratch = false;
+        int subTransforms = 1;
+        int twiddleOffset = 2 * size;
+
+        for(int radix : mFactors)
+        {
+            int next = radix * subTransforms;
+            int stride = 2 * (size / next);
+            float[] in = resultsInScratch ? scratch : samples;
+            int inOffset = resultsInScratch ? 0 : offset;
+            float[] out = resultsInScratch ? samples : scratch;
+            int outOffset = resultsInScratch ? offset : 0;
+
+            switch(radix)
+            {
+                case 2 -> mFFT.passf2(stride, subTransforms, in, inOffset, out, outOffset, twiddleOffset, 1);
+                case 3 -> mFFT.passf3(stride, subTransforms, in, inOffset, out, outOffset, twiddleOffset, 1);
+                case 4 -> mFFT.passf4(stride, subTransforms, in, inOffset, out, outOffset, twiddleOffset, 1);
+                default -> mFFT.passf5(stride, subTransforms, in, inOffset, out, outOffset, twiddleOffset, 1);
+            }
+
+            resultsInScratch = !resultsInScratch;
+            subTransforms = next;
+            twiddleOffset += (radix - 1) * stride;
+        }
+
+        if(resultsInScratch)
+        {
+            System.arraycopy(scratch, 0, samples, offset, 2 * size);
+        }
+
+        final float scale = mScale;
+        final int end = offset + 2 * size;
+
+        for(int x = offset; x < end; x++)
+        {
+            samples[x] *= scale;
+        }
+    }
+}

src/test/java/io/github/dsheirer/audio/AudioSegmentRolloverTest.java

@@ -0,0 +1,59 @@
+/*
+ * *****************************************************************************
+ * Copyright (C) 2014-2026 Dennis Sheirer
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program.  If not, see <http://www.gnu.org/licenses/>
+ * ****************************************************************************
+ */
+
+package io.github.dsheirer.audio;
+
+import static org.junit.jupiter.api.Assertions.assertEquals;
+import static org.junit.jupiter.api.Assertions.assertTrue;
+
+import io.github.dsheirer.alias.AliasList;
+import java.util.ArrayList;
+import java.util.Collections;
+import java.util.List;
+import org.junit.jupiter.api.Test;
+
+/**
+ * Tests audio segment rollover at the maximum audio segment length.
+ */
+public class AudioSegmentRolloverTest
+{
+    private static final float[] ONE_SECOND_OF_AUDIO = new float[8000];
+
+    @Test
+    public void defaultMaximumSegmentLengthIsOneMinute()
+    {
+        AudioModule module = new AudioModule(new AliasList("test"), Collections.emptyList());
+        List<AudioSegment> segments = new ArrayList<>();
+        module.setAudioSegmentListener(segments::add);
+
+        for(int seconds = 0; seconds < 60; seconds++)
+        {
+            module.addAudio(ONE_SECOND_OF_AUDIO);
+        }
+
+        assertEquals(1, segments.size(), "A full minute of audio should fit in a single segment");
+
+        module.addAudio(ONE_SECOND_OF_AUDIO);
+
+        assertEquals(2, segments.size(), "Audio beyond one minute should roll over to a new segment");
+        assertEquals(60_000, segments.get(0).getDuration());
+        assertTrue(segments.get(0).isComplete(), "First segment should be closed");
+        assertTrue(segments.get(1).isLinkedTo(segments.get(0)), "New segment should link to the first segment");
+    }
+}

src/test/java/io/github/dsheirer/audio/playback/AudioPlaybackPriorityTest.java

@@ -0,0 +1,170 @@
+/*
+ * *****************************************************************************
+ * Copyright (C) 2014-2026 Dennis Sheirer
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program.  If not, see <http://www.gnu.org/licenses/>
+ * ****************************************************************************
+ */
+
+package io.github.dsheirer.audio.playback;
+
+import static org.junit.jupiter.api.Assertions.assertEquals;
+import static org.junit.jupiter.api.Assertions.assertFalse;
+import static org.junit.jupiter.api.Assertions.assertNull;
+import static org.junit.jupiter.api.Assertions.assertSame;
+import static org.junit.jupiter.api.Assertions.assertTrue;
+
+import io.github.dsheirer.alias.AliasList;
+import io.github.dsheirer.audio.AudioSegment;
+import io.github.dsheirer.preference.UserPreferences;
+import java.util.ArrayList;
+import java.util.List;
+import org.junit.jupiter.api.AfterEach;
+import org.junit.jupiter.api.BeforeEach;
+import org.junit.jupiter.api.Test;
+
+/**
+ * Tests that a higher priority audio segment isn't displaced by lower priority audio during playback (issue #2333).
+ */
+public class AudioPlaybackPriorityTest
+{
+    private static final float[] AUDIO = new float[AudioChannel.SAMPLES_PER_INTERVAL];
+    private AudioChannel mChannel;
+
+    @BeforeEach
+    public void setup()
+    {
+        mChannel = new AudioChannel(new UserPreferences(), "TEST");
+    }
+
+    @AfterEach
+    public void teardown()
+    {
+        mChannel.dispose();
+    }
+
+    private static AudioSegment segment(int priority)
+    {
+        AudioSegment segment = new AudioSegment(new AliasList("test"), 0);
+        segment.incrementConsumerCount();
+        segment.monitorPriorityProperty().set(priority);
+        segment.addAudio(AUDIO);
+        return segment;
+    }
+
+    /**
+     * Pulls audio until the buffered audio (start tone and first frame) is exhausted and the channel is waiting on the
+     * audio segment for more audio.
+     */
+    private void drainBufferedAudio()
+    {
+        while(mChannel.getAudio() != null)
+        {
+            //Discard buffered audio
+        }
+    }
+
+    private void pullIntervals(int count)
+    {
+        for(int x = 0; x < count; x++)
+        {
+            mChannel.getAudio();
+        }
+    }
+
+    @Test
+    public void liveSegmentSurvivesDecoderGapWithLowerPriorityQueued()
+    {
+        AudioSegment priority1 = segment(1);
+        AudioSegment priority2 = segment(2);
+        mChannel.play(priority1);
+        mChannel.getAudio();
+        mChannel.play(priority2);
+        drainBufferedAudio();
+
+        //300 ms without audio exceeds a missed P25 LDU
+        pullIntervals(15);
+
+        assertTrue(mChannel.hasAudioSegment(), "Live segment should still be assigned");
+        assertSame(priority2, mChannel.peekQueuedAudioSegment(), "Queued lower priority segment should not have started");
+
+        priority1.addAudio(AUDIO);
+        assertTrue(mChannel.getAudio() != null, "Audio arriving after the gap should play");
+    }
+
+    @Test
+    public void stalledSegmentIsAbandonedSoChannelIsReleased()
+    {
+        mChannel.play(segment(1));
+        mChannel.getAudio();
+        drainBufferedAudio();
+        pullIntervals(AudioChannel.MAX_STALLED_INTERVALS + 1);
+
+        assertFalse(mChannel.hasAudioSegment(), "Stalled segment should be released");
+    }
+
+    @Test
+    public void completedSegmentIsReleasedWithoutWaitingForStallTimeout()
+    {
+        AudioSegment segment = segment(1);
+        mChannel.play(segment);
+        mChannel.getAudio();
+        segment.completeProperty().set(true);
+        drainBufferedAudio();
+        pullIntervals(2);
+
+        assertFalse(mChannel.hasAudioSegment(), "Completed segment should be released");
+    }
+
+    @Test
+    public void higherPriorityWaitingSegmentReplacesLowerPriorityQueuedSegment()
+    {
+        AudioSegment priority1 = segment(1);
+        AudioSegment priority3 = segment(3);
+        mChannel.play(priority3);
+        List<AudioSegment> waiting = new ArrayList<>(List.of(priority1));
+
+        AudioPlaybackManager.replaceLowerPriorityQueuedSegments(waiting, List.of(mChannel));
+
+        assertSame(priority1, mChannel.peekQueuedAudioSegment());
+        assertEquals(List.of(priority3), waiting, "Displaced segment should return to the waiting list");
+    }
+
+    @Test
+    public void equalAndLowerPriorityWaitingSegmentsDoNotReplaceQueuedSegment()
+    {
+        AudioSegment queued = segment(2);
+        mChannel.play(queued);
+
+        for(int priority: new int[]{2, 3})
+        {
+            AudioSegment other = segment(priority);
+            List<AudioSegment> waiting = new ArrayList<>(List.of(other));
+            AudioPlaybackManager.replaceLowerPriorityQueuedSegments(waiting, List.of(mChannel));
+
+            assertSame(queued, mChannel.peekQueuedAudioSegment());
+            assertEquals(List.of(other), waiting);
+        }
+    }
+
+    @Test
+    public void noReplacementWhenNothingIsQueued()
+    {
+        List<AudioSegment> waiting = new ArrayList<>(List.of(segment(1)));
+        AudioPlaybackManager.replaceLowerPriorityQueuedSegments(waiting, List.of(mChannel));
+
+        assertNull(mChannel.peekQueuedAudioSegment());
+        assertEquals(1, waiting.size());
+    }
+}

src/test/java/io/github/dsheirer/audio/playback/AudioProviderPcmTest.java

@@ -0,0 +1,44 @@
+/*
+ * *****************************************************************************
+ * Copyright (C) 2014-2026 Dennis Sheirer
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program.  If not, see <http://www.gnu.org/licenses/>
+ * ****************************************************************************
+ */
+package io.github.dsheirer.audio.playback;
+
+import static org.junit.jupiter.api.Assertions.assertEquals;
+
+import org.junit.jupiter.api.Test;
+
+/**
+ * Unit tests for audio provider sample conversion
+ */
+class AudioProviderPcmTest
+{
+    @Test
+    void outOfRangeSamplesAreLimitedInsteadOfWrapping()
+    {
+        assertEquals(Short.MAX_VALUE, AudioProvider.toPcm(1.35f));
+        assertEquals(-Short.MAX_VALUE, AudioProvider.toPcm(-26.0f));
+    }
+
+    @Test
+    void inRangeSamplesAreScaled()
+    {
+        assertEquals(0, AudioProvider.toPcm(0.0f));
+        assertEquals(16383, AudioProvider.toPcm(0.5f));
+        assertEquals(Short.MAX_VALUE, AudioProvider.toPcm(1.0f));
+    }
+}

src/test/java/io/github/dsheirer/dsp/am/AmAudioNormalizerTest.java

@@ -0,0 +1,121 @@
+/*
+ * *****************************************************************************
+ * Copyright (C) 2014-2026 Dennis Sheirer
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program.  If not, see <http://www.gnu.org/licenses/>
+ * ****************************************************************************
+ */
+package io.github.dsheirer.dsp.am;
+
+import static org.junit.jupiter.api.Assertions.assertEquals;
+import static org.junit.jupiter.api.Assertions.assertTrue;
+
+import org.junit.jupiter.api.Test;
+
+/**
+ * Unit tests for the AM audio normalizer
+ */
+class AmAudioNormalizerTest
+{
+    private static final double SAMPLE_RATE = 25000.0;
+    private static final float MODULATION = 0.8f;
+
+    private static float envelope(float carrier, int sample)
+    {
+        return carrier * (1.0f + MODULATION * (float)Math.cos(2.0 * Math.PI * 1000.0 / SAMPLE_RATE * sample));
+    }
+
+    @Test
+    void outputFollowsModulationDepthAtAnyCarrierLevel()
+    {
+        for(float carrier: new float[]{0.0005f, 0.002f, 0.01f, 0.03f, 0.1f})
+        {
+            checkOutput(carrier);
+        }
+    }
+
+    private static void checkOutput(float carrier)
+    {
+        AmAudioNormalizer normalizer = new AmAudioNormalizer(SAMPLE_RATE);
+        double sum = 0.0;
+        float peak = 0.0f;
+        int settle = (int)SAMPLE_RATE;
+        int count = (int)SAMPLE_RATE;
+
+        for(int x = 0; x < settle + count; x++)
+        {
+            float audio = normalizer.process(envelope(carrier, x));
+
+            if(x >= settle)
+            {
+                sum += audio;
+                peak = Math.max(peak, Math.abs(audio));
+            }
+        }
+
+        assertEquals(0.6f, peak, 0.02f, "Peak");
+        assertEquals(0.0, sum / count, 0.002, "DC");
+    }
+
+    @Test
+    void transmissionStartHasNoTransient()
+    {
+        AmAudioNormalizer normalizer = new AmAudioNormalizer(SAMPLE_RATE);
+
+        for(int x = 0; x < (int)SAMPLE_RATE; x++)
+        {
+            assertTrue(Math.abs(normalizer.process(envelope(0.01f, x))) < 0.8f, "Transient at sample " + x);
+        }
+    }
+
+    @Test
+    void noiseAfterCarrierDropIsNotAmplifiedToCarrierLevel()
+    {
+        AmAudioNormalizer normalizer = new AmAudioNormalizer(SAMPLE_RATE);
+
+        for(int x = 0; x < (int)SAMPLE_RATE; x++)
+        {
+            normalizer.process(envelope(0.01f, x));
+        }
+
+        java.util.Random random = new java.util.Random(1);
+        float peak = 0.0f;
+
+        //Noise is 40 dB below the carrier.  Skip the carrier estimate decay.
+        for(int x = 0; x < (int)(SAMPLE_RATE * 0.5); x++)
+        {
+            float audio = normalizer.process(0.0001f * (1.0f + random.nextFloat()));
+
+            if(x > (int)(SAMPLE_RATE * 0.2))
+            {
+                peak = Math.max(peak, Math.abs(audio));
+            }
+        }
+
+        assertTrue(peak < 0.05f, "Noise peak " + peak);
+    }
+
+    @Test
+    void outputIsLimited()
+    {
+        AmAudioNormalizer normalizer = new AmAudioNormalizer(SAMPLE_RATE);
+
+        for(int x = 0; x < 1000; x++)
+        {
+            normalizer.process(0.001f);
+        }
+
+        assertTrue(normalizer.process(1.0f) <= 0.95f);
+    }
+}

src/test/java/io/github/dsheirer/dsp/am/SquelchingAMDemodulatorTest.java

@@ -0,0 +1,105 @@
+/*
+ * *****************************************************************************
+ * Copyright (C) 2014-2026 Dennis Sheirer
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program.  If not, see <http://www.gnu.org/licenses/>
+ * ****************************************************************************
+ */
+package io.github.dsheirer.dsp.am;
+
+import static org.junit.jupiter.api.Assertions.assertEquals;
+import static org.junit.jupiter.api.Assertions.assertTrue;
+
+import org.junit.jupiter.api.Test;
+
+/**
+ * Unit tests for the AM demodulator squelch transitions
+ */
+class SquelchingAMDemodulatorTest
+{
+    private static final int SAMPLE_RATE = 25000;
+    private static final int BUFFER = 1024;
+    private static final double TONE = 1000.0;
+
+    /**
+     * Demodulates silence, then a transmission, then silence.
+     */
+    private static float[] transmission(float carrier)
+    {
+        SquelchingAMDemodulator demodulator = new SquelchingAMDemodulator(-78.0f, false, 6000.0);
+        demodulator.setSampleRate(SAMPLE_RATE);
+        int buffers = 150;
+        float[] audio = new float[BUFFER * buffers];
+
+        for(int b = 0; b < buffers; b++)
+        {
+            float[] i = new float[BUFFER];
+            float[] q = new float[BUFFER];
+
+            if(b >= 30 && b < 100)
+            {
+                for(int x = 0; x < BUFFER; x++)
+                {
+                    int sample = b * BUFFER + x;
+                    i[x] = carrier * (1.0f + 0.8f * (float)Math.cos(2.0 * Math.PI * TONE * sample / SAMPLE_RATE));
+                }
+            }
+
+            System.arraycopy(demodulator.demodulate(i, q), 0, audio, b * BUFFER, BUFFER);
+        }
+
+        return audio;
+    }
+
+    @Test
+    void transmissionHasNoClicks()
+    {
+        for(float carrier: new float[]{0.001f, 0.01f, 0.1f})
+        {
+            float[] audio = transmission(carrier);
+            float peak = 0.0f;
+            float step = 0.0f;
+
+            for(int x = 1; x < audio.length; x++)
+            {
+                peak = Math.max(peak, Math.abs(audio[x]));
+                step = Math.max(step, Math.abs(audio[x] - audio[x - 1]));
+            }
+
+            //Expected 80% modulated peak is 0.6 and the largest step of the 1 kHz tone is 0.15
+            assertTrue(peak < 0.7f, "Peak " + peak + " for carrier " + carrier);
+            assertTrue(step < 0.2f, "Step " + step + " for carrier " + carrier);
+        }
+    }
+
+    @Test
+    void audioEndsWithTheTransmission()
+    {
+        float[] audio = transmission(0.01f);
+        int last = 0;
+
+        for(int x = 0; x < audio.length; x++)
+        {
+            if(audio[x] != 0.0f)
+            {
+                last = x;
+            }
+        }
+
+        //Audio is delayed by 32 ms, so it can't run past the end of the transmission plus the delay.
+        int end = 100 * BUFFER;
+        assertTrue(last <= end + SAMPLE_RATE * 0.032, "Last audio sample " + last + " for end at " + end);
+        assertEquals(0.0f, audio[audio.length - 1]);
+    }
+}

src/test/java/io/github/dsheirer/dsp/filter/ChannelFilterDesignerTest.java

@@ -0,0 +1,98 @@
+/*
+ * *****************************************************************************
+ * Copyright (C) 2014-2026 Dennis Sheirer
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program.  If not, see <http://www.gnu.org/licenses/>
+ * ****************************************************************************
+ */
+package io.github.dsheirer.dsp.filter;
+
+import static org.junit.jupiter.api.Assertions.assertTrue;
+
+import org.junit.jupiter.api.Test;
+
+/**
+ * Unit tests for the channel filter design
+ */
+class ChannelFilterDesignerTest
+{
+    private static final double[] BANDWIDTHS = {3000.0, 5000.0, 6000.0, 7500.0, 8333.0, 12500.0, 15000.0, 25000.0};
+
+    /**
+     * Each channel filter must be valid across decimated sample rates, which includes rates where the remez designer
+     * previously produced a filter with a large response spike at half of the sample rate.
+     */
+    @Test
+    void channelFilterResponseIsValidForDecimatedSampleRates()
+    {
+        for(double bandwidth: BANDWIDTHS)
+        {
+            for(double sampleRate = bandwidth; sampleRate < 4.0 * bandwidth; sampleRate += bandwidth / 32.0)
+            {
+                check(sampleRate, bandwidth);
+            }
+        }
+    }
+
+    @Test
+    void tunerDerivedSampleRates()
+    {
+        check(11718.75, 3000.0);
+        check(19531.25, 5000.0);
+        check(50000.0, 15000.0);
+        check(29296.875, 7500.0);
+        check(48828.125, 12500.0);
+        check(25000.0, 7500.0);
+    }
+
+    /**
+     * These sample rates use the fallback filter design, which must keep the same bandwidth as the remez design.
+     */
+    @Test
+    void fallbackFilterKeepsChannelBandwidth()
+    {
+        checkPassBand(11718.75, 3000.0);
+        checkPassBand(19531.25, 5000.0);
+        checkPassBand(50000.0, 15000.0);
+    }
+
+    private static void checkPassBand(double sampleRate, double bandwidth)
+    {
+        float[] coefficients = ChannelFilterDesigner.design(sampleRate, bandwidth);
+        double response = ChannelFilterDesigner.getResponseDb(coefficients, bandwidth * .4, sampleRate) -
+            ChannelFilterDesigner.getResponseDb(coefficients, 0.0, sampleRate);
+        assertTrue(response > -1.0, "Pass band edge response [" + response + " dB] at sample rate [" + sampleRate + "]");
+    }
+
+    private static void check(double sampleRate, double bandwidth)
+    {
+        float[] coefficients = ChannelFilterDesigner.design(sampleRate, bandwidth);
+        assertTrue(ChannelFilterDesigner.isValidFilterResponse(coefficients, sampleRate, (int)(bandwidth * .4), (int)(bandwidth * .5)),
+            "Filter response for sample rate [" + sampleRate + "] bandwidth [" + bandwidth + "]");
+    }
+
+    @Test
+    void responseCheckRejectsSpikeAtNyquist()
+    {
+        //Low-pass moving average with an added alternating sequence that peaks at half of the sample rate.
+        float[] coefficients = new float[31];
+
+        for(int x = 0; x < coefficients.length; x++)
+        {
+            coefficients[x] = 1.0f / coefficients.length + (x % 2 == 0 ? 0.1f : -0.1f);
+        }
+
+        assertTrue(!ChannelFilterDesigner.isValidFilterResponse(coefficients, 25000.0, 3000, 4000));
+    }
+}

src/test/java/io/github/dsheirer/dsp/squelch/AdaptiveSquelchTest.java

@@ -0,0 +1,387 @@
+/*
+ * *****************************************************************************
+ * Copyright (C) 2014-2026 Dennis Sheirer
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program.  If not, see <http://www.gnu.org/licenses/>
+ * ****************************************************************************
+ */
+package io.github.dsheirer.dsp.squelch;
+
+import static org.junit.jupiter.api.Assertions.assertEquals;
+import static org.junit.jupiter.api.Assertions.assertFalse;
+import static org.junit.jupiter.api.Assertions.assertTrue;
+
+import io.github.dsheirer.source.SourceEvent;
+import java.util.ArrayList;
+import java.util.List;
+import java.util.Random;
+import org.junit.jupiter.api.Test;
+
+/**
+ * Unit tests for the adaptive squelch
+ */
+class AdaptiveSquelchTest
+{
+    private static final int SAMPLE_RATE = 25000;
+    private static final float THRESHOLD_DB = -78.0f;
+    private static final float NOISE = (float)Math.pow(10.0, -9.0); //-90 dB
+
+    private static AdaptiveSquelch squelch(int sampleRate, boolean autoTrack)
+    {
+        AdaptiveSquelch squelch = new AdaptiveSquelch(THRESHOLD_DB, autoTrack, 6000.0);
+        squelch.setSampleRate(sampleRate);
+        return squelch;
+    }
+
+    private static void process(AdaptiveSquelch squelch, float power, double seconds, int sampleRate)
+    {
+        for(int x = 0; x < (int)(seconds * sampleRate); x++)
+        {
+            squelch.process(power);
+        }
+    }
+
+    /**
+     * Seconds of samples at the power level until the audio is disabled and until the squelch closes.
+     */
+    private static double[] closeTimes(float signal, int sampleRate)
+    {
+        AdaptiveSquelch squelch = squelch(sampleRate, false);
+        process(squelch, signal, 0.5, sampleRate);
+        assertTrue(squelch.isUnmuted());
+        double audio = -1.0;
+
+        for(int x = 0; x < sampleRate; x++)
+        {
+            squelch.process(NOISE);
+
+            if(audio < 0.0 && !squelch.isAudioEnabled())
+            {
+                audio = (double)x / sampleRate;
+            }
+
+            if(squelch.isMuted())
+            {
+                return new double[]{audio, (double)x / sampleRate};
+            }
+        }
+
+        throw new AssertionError("Squelch didn't close");
+    }
+
+    @Test
+    void closeTimeIsIndependentOfSignalLevelAndSampleRate()
+    {
+        for(int sampleRate: new int[]{6250, 25000, 50000})
+        {
+            for(float signal: new float[]{1E-7f, 1E-6f, 1E-4f, 1E-2f})
+            {
+                double[] times = closeTimes(signal, sampleRate);
+                assertEquals(0.0175, times[0], 0.0085, "Audio disable " + signal + " at " + sampleRate);
+                assertEquals(0.1175, times[1], 0.0085, "Close " + signal + " at " + sampleRate);
+            }
+        }
+    }
+
+    @Test
+    void startsMuted()
+    {
+        AdaptiveSquelch squelch = squelch(SAMPLE_RATE, false);
+        assertTrue(squelch.isMuted());
+        assertFalse(squelch.isAudioEnabled());
+    }
+
+    @Test
+    void shortNoiseBurstDoesNotOpen()
+    {
+        AdaptiveSquelch squelch = squelch(SAMPLE_RATE, false);
+        process(squelch, NOISE, 0.1, SAMPLE_RATE);
+        process(squelch, 1E-4f, 0.005, SAMPLE_RATE);
+        process(squelch, NOISE, 0.1, SAMPLE_RATE);
+        assertTrue(squelch.isMuted());
+    }
+
+    @Test
+    void hysteresisHoldsOpenBelowOpenThreshold()
+    {
+        AdaptiveSquelch squelch = squelch(SAMPLE_RATE, false);
+        float threshold = (float)Math.pow(10.0, THRESHOLD_DB / 10.0);
+        process(squelch, threshold * 1.2f, 0.1, SAMPLE_RATE);
+        assertTrue(squelch.isUnmuted());
+        process(squelch, threshold * 0.6f, 2.0, SAMPLE_RATE); //2 dB below open, above close
+        assertTrue(squelch.isAudioEnabled());
+    }
+
+    @Test
+    void fadeShorterThanHangKeepsCallOpen()
+    {
+        AdaptiveSquelch squelch = squelch(SAMPLE_RATE, false);
+        process(squelch, 1E-5f, 0.1, SAMPLE_RATE);
+        process(squelch, NOISE, 0.06, SAMPLE_RATE);
+        assertFalse(squelch.isAudioEnabled());
+        assertTrue(squelch.isUnmuted());
+        process(squelch, 1E-5f, 0.03, SAMPLE_RATE);
+        assertTrue(squelch.isAudioEnabled());
+    }
+
+    @Test
+    void lowFrequencyModulationDoesNotDisableAudio()
+    {
+        AdaptiveSquelch squelch = squelch(SAMPLE_RATE, false);
+        float threshold = (float)Math.pow(10.0, THRESHOLD_DB / 10.0);
+        process(squelch, threshold * 2.0f, 0.1, SAMPLE_RATE);
+
+        //Carrier 3 dB over the open threshold with 100% modulation at 100 Hz
+        for(int x = 0; x < SAMPLE_RATE * 2; x++)
+        {
+            double envelope = 1.0 + Math.cos(2.0 * Math.PI * 100.0 * x / SAMPLE_RATE);
+            squelch.process((float)(threshold * 2.0 / 1.5 * envelope * envelope));
+            assertTrue(squelch.isAudioEnabled(), "Audio disabled at sample " + x);
+        }
+    }
+
+    /**
+     * Sample powers with the exponential distribution of complex gaussian noise.
+     */
+    private static void noise(AdaptiveSquelch squelch, float power, double seconds, int sampleRate, Random random)
+    {
+        for(int x = 0; x < (int)(seconds * sampleRate); x++)
+        {
+            squelch.process((float)(-Math.log(1.0 - random.nextDouble()) * power));
+        }
+    }
+
+    /**
+     * Sample powers for a steady carrier with noise 20 dB below the carrier
+     */
+    private static void carrier(AdaptiveSquelch squelch, float power, double seconds, int sampleRate, Random random)
+    {
+        double sigma = Math.sqrt(power * 0.01 / 2.0);
+        double amplitude = Math.sqrt(power);
+
+        for(int x = 0; x < (int)(seconds * sampleRate); x++)
+        {
+            double i = amplitude + sigma * random.nextGaussian();
+            double q = sigma * random.nextGaussian();
+            squelch.process((float)(i * i + q * q));
+        }
+    }
+
+    @Test
+    void thresholdBelowNoiseFloorDoesNotLatchOpen()
+    {
+        Random random = new Random(1);
+        AdaptiveSquelch squelch = squelch(SAMPLE_RATE, true);
+        float noise = (float)Math.pow(10.0, -7.4); //-74 dB is above the -78 dB threshold
+
+        for(int x = 0; x < SAMPLE_RATE * 30; x++)
+        {
+            squelch.process((float)(-Math.log(1.0 - random.nextDouble()) * noise));
+            assertTrue(squelch.isMuted(), "Opened at sample " + x);
+        }
+
+        assertEquals(-68.0f, squelch.getSquelchThreshold(), 0.5f);
+    }
+
+    @Test
+    void transmissionOpensOverLearnedNoiseFloor()
+    {
+        Random random = new Random(2);
+        AdaptiveSquelch squelch = squelch(SAMPLE_RATE, true);
+        noise(squelch, 4E-8f, 2.0, SAMPLE_RATE, random); //-74 dB
+        carrier(squelch, 4E-7f, 1.0, SAMPLE_RATE, random); //-64 dB
+        assertTrue(squelch.isAudioEnabled());
+        noise(squelch, 4E-8f, 0.5, SAMPLE_RATE, random);
+        assertTrue(squelch.isMuted());
+        assertEquals(-68.0f, squelch.getSquelchThreshold(), 0.5f);
+    }
+
+    @Test
+    void userMarginAboveMinimumIsKept()
+    {
+        Random random = new Random(3);
+        AdaptiveSquelch squelch = squelch(SAMPLE_RATE, true);
+        noise(squelch, 1E-9f, 2.0, SAMPLE_RATE, random); //-90 dB, with a -78 dB threshold
+        assertEquals(THRESHOLD_DB, squelch.getSquelchThreshold(), 0.5f);
+    }
+
+    @Test
+    void autoTrackKeepsDecibelMarginWhenNoiseFloorRises()
+    {
+        Random random = new Random(4);
+        AdaptiveSquelch squelch = squelch(SAMPLE_RATE, true);
+        noise(squelch, 1E-9f, 2.0, SAMPLE_RATE, random); //-90 dB
+
+        //Raise the noise floor 16 dB in steps that stay under the squelch threshold.
+        for(int step = 1; step <= 8; step++)
+        {
+            noise(squelch, 1E-9f * (float)Math.pow(10.0, step * 0.2), 11.0, SAMPLE_RATE, random);
+            assertTrue(squelch.isMuted(), "Opened at step " + step);
+        }
+
+        assertEquals(THRESHOLD_DB + 16.0f, squelch.getSquelchThreshold(), 0.5f);
+    }
+
+    @Test
+    void steadyCarrierPresentAtStartPassesUntilTimeoutThenMutes()
+    {
+        Random random = new Random(5);
+        AdaptiveSquelch squelch = squelch(SAMPLE_RATE, true);
+        carrier(squelch, 2.5E-7f, 59.0, SAMPLE_RATE, random); //-66 dB
+        assertTrue(squelch.isAudioEnabled());
+        carrier(squelch, 2.5E-7f, 3.0, SAMPLE_RATE, random);
+        assertTrue(squelch.isMuted());
+        carrier(squelch, 2.5E-7f, 30.0, SAMPLE_RATE, random);
+        assertTrue(squelch.isMuted());
+    }
+
+    @Test
+    void steadyCarrierAfterNoisePassesUntilTimeoutThenMutes()
+    {
+        Random random = new Random(6);
+        AdaptiveSquelch squelch = squelch(SAMPLE_RATE, true);
+        noise(squelch, 4E-8f, 2.0, SAMPLE_RATE, random);
+        carrier(squelch, 4E-7f, 59.0, SAMPLE_RATE, random);
+        assertTrue(squelch.isAudioEnabled());
+        carrier(squelch, 4E-7f, 3.0, SAMPLE_RATE, random);
+        assertTrue(squelch.isMuted());
+    }
+
+    @Test
+    void transmissionsAreHeardAfterCarrierTimeoutEnds()
+    {
+        Random random = new Random(7);
+        AdaptiveSquelch squelch = squelch(SAMPLE_RATE, true);
+        noise(squelch, 4E-8f, 2.0, SAMPLE_RATE, random);
+        carrier(squelch, 4E-7f, 63.0, SAMPLE_RATE, random);
+        assertTrue(squelch.isMuted());
+
+        noise(squelch, 4E-8f, 1.0, SAMPLE_RATE, random);
+        assertEquals(-68.0f, squelch.getSquelchThreshold(), 0.5f);
+        carrier(squelch, 4E-7f, 1.0, SAMPLE_RATE, random);
+        assertTrue(squelch.isAudioEnabled());
+    }
+
+    @Test
+    void autoTrackDisabledUsesUserThreshold()
+    {
+        Random random = new Random(8);
+        AdaptiveSquelch squelch = squelch(SAMPLE_RATE, false);
+        noise(squelch, 4E-8f, 2.0, SAMPLE_RATE, random); //Noise above the threshold opens the squelch
+        assertTrue(squelch.isUnmuted());
+        assertEquals(THRESHOLD_DB, squelch.getSquelchThreshold(), 0.01f);
+    }
+
+    /**
+     * Requests the threshold and returns the user threshold notification value.
+     */
+    private static double requestThreshold(AdaptiveSquelch squelch, double threshold)
+    {
+        List<SourceEvent> events = new ArrayList<>();
+        squelch.setSourceEventListener(events::add);
+        squelch.receive(SourceEvent.requestSquelchThreshold(null, threshold));
+        squelch.setSourceEventListener(null);
+        return events.stream().filter(event -> event.getEvent() == SourceEvent.Event.NOTIFICATION_SQUELCH_USER_THRESHOLD)
+            .findFirst().orElseThrow().getValue().doubleValue();
+    }
+
+    @Test
+    void thresholdChangeDuringTimedOutCarrierIsRelativeToNoiseFloor()
+    {
+        Random random = new Random(9);
+        AdaptiveSquelch squelch = squelch(SAMPLE_RATE, true);
+        noise(squelch, 4E-8f, 2.0, SAMPLE_RATE, random); //-74 dB with a -68 dB threshold
+        carrier(squelch, 4E-7f, 63.0, SAMPLE_RATE, random); //-64 dB with a -58 dB threshold
+        assertEquals(-58.0f, squelch.getSquelchThreshold(), 0.5f);
+
+        //One dB up from the displayed threshold saves one dB over the -68 dB threshold, not -57 dB
+        assertEquals(-67.0, requestThreshold(squelch, squelch.getSquelchThreshold() + 1.0), 0.5);
+        assertEquals(-57.0f, squelch.getSquelchThreshold(), 0.5f);
+
+        //The setting applies when the carrier ends
+        noise(squelch, 4E-8f, 1.0, SAMPLE_RATE, random);
+        assertEquals(-67.0f, squelch.getSquelchThreshold(), 0.5f);
+    }
+
+    @Test
+    void thresholdChangeBelowMinimumMarginIsLimited()
+    {
+        Random random = new Random(10);
+        AdaptiveSquelch squelch = squelch(SAMPLE_RATE, true);
+        noise(squelch, 4E-8f, 2.0, SAMPLE_RATE, random); //-74 dB
+        assertEquals(-68.0, requestThreshold(squelch, -72.0), 0.5);
+        assertEquals(-68.0f, squelch.getSquelchThreshold(), 0.5f);
+    }
+
+    @Test
+    void thresholdChangeWithAutoTrackDisabledIsUnchanged()
+    {
+        AdaptiveSquelch squelch = squelch(SAMPLE_RATE, false);
+        assertEquals(-72.0, requestThreshold(squelch, -72.0), 0.01);
+        assertEquals(-72.0f, squelch.getSquelchThreshold(), 0.01f);
+    }
+
+    /**
+     * Sample powers for a carrier with noise 20 dB below the carrier and bursts of low frequency voice-like modulation.
+     */
+    private static void voiceCarrier(AdaptiveSquelch squelch, float power, double seconds, int sampleRate, Random random)
+    {
+        double sigma = Math.sqrt(power * 0.01 / 2.0);
+        double amplitude = Math.sqrt(power);
+
+        for(int x = 0; x < (int)(seconds * sampleRate); x++)
+        {
+            double time = (double)x / sampleRate;
+            double modulation = 0.3 * Math.cos(2.0 * Math.PI * 500.0 * time) + 0.2 * Math.cos(2.0 * Math.PI * 800.0 * time);
+            double i = amplitude * (1.0 + modulation) + sigma * random.nextGaussian();
+            double q = sigma * random.nextGaussian();
+            squelch.process((float)(i * i + q * q));
+        }
+    }
+
+    @Test
+    void carrierWithVoiceModulationDoesNotTimeOut()
+    {
+        Random random = new Random(11);
+        AdaptiveSquelch squelch = squelch(SAMPLE_RATE, true);
+        noise(squelch, 4E-8f, 2.0, SAMPLE_RATE, random);
+        voiceCarrier(squelch, 4E-7f, 190.0, SAMPLE_RATE, random);
+        assertTrue(squelch.isAudioEnabled());
+        assertEquals(-68.0f, squelch.getSquelchThreshold(), 0.5f);
+    }
+
+    @Test
+    void voiceOnTimedOutCarrierReopensSquelch()
+    {
+        Random random = new Random(12);
+        AdaptiveSquelch squelch = squelch(SAMPLE_RATE, true);
+        noise(squelch, 4E-8f, 2.0, SAMPLE_RATE, random);
+        carrier(squelch, 4E-7f, 63.0, SAMPLE_RATE, random);
+        assertTrue(squelch.isMuted());
+        voiceCarrier(squelch, 4E-7f, 4.0, SAMPLE_RATE, random);
+        assertEquals(-68.0f, squelch.getSquelchThreshold(), 0.5f);
+        assertTrue(squelch.isAudioEnabled());
+    }
+
+    @Test
+    void voiceOnCarrierPresentAtStartReopensSquelch()
+    {
+        Random random = new Random(13);
+        AdaptiveSquelch squelch = squelch(SAMPLE_RATE, true);
+        carrier(squelch, 4E-7f, 63.0, SAMPLE_RATE, random);
+        assertTrue(squelch.isMuted());
+        voiceCarrier(squelch, 4E-7f, 4.0, SAMPLE_RATE, random);
+        assertTrue(squelch.isAudioEnabled());
+    }
+}

src/test/java/io/github/dsheirer/dsp/squelch/NoiseSquelchTest.java

@@ -0,0 +1,127 @@
+/*
+ * *****************************************************************************
+ * Copyright (C) 2014-2026 Dennis Sheirer
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program.  If not, see <http://www.gnu.org/licenses/>
+ * ****************************************************************************
+ */
+
+package io.github.dsheirer.dsp.squelch;
+
+import static org.junit.jupiter.api.Assertions.assertEquals;
+import static org.junit.jupiter.api.Assertions.assertTrue;
+
+import io.github.dsheirer.dsp.filter.ChannelFilterDesigner;
+import io.github.dsheirer.dsp.filter.fir.real.RealFIRFilter;
+import io.github.dsheirer.dsp.fm.ScalarFMDemodulator;
+import java.util.Arrays;
+import java.util.Random;
+import org.junit.jupiter.api.Test;
+
+/**
+ * Unit tests for the noise squelch normalization across channel bandwidths and sample rates.
+ */
+class NoiseSquelchTest
+{
+    private static final double[][] CHANNELS = {{7500.0, 25000.0}, {7500.0, 25600.0}, {7500.0, 18750.0},
+            {12500.0, 25000.0}, {12500.0, 37500.0}, {12500.0, 48828.125}, {25000.0, 50000.0}};
+    private static final int BUFFER_SIZE = 2048;
+    private static final double SECONDS = 5.0;
+    private static final double NOISE_LEVEL = 0.01;
+
+    /**
+     * A noise-only channel must stay squelched with the default thresholds.  A 7.5 kHz channel at 25 kHz has a noise
+     * variance between the default open and close thresholds, which holds the squelch open if it's not normalized.
+     */
+    @Test
+    void noiseOnlyChannelStaysSquelched()
+    {
+        for(double[] channel: CHANNELS)
+        {
+            double passed = process(channel[0], channel[1], null);
+            assertEquals(0.0, passed, 0.01, "Noise passed for bandwidth [" + channel[0] + "] rate [" + channel[1] + "]");
+        }
+    }
+
+    @Test
+    void signalOpensSquelch()
+    {
+        for(double[] channel: CHANNELS)
+        {
+            double passed = process(channel[0], channel[1], 12.0);
+            assertTrue(passed > 0.95, "Signal blocked [" + passed + "] for bandwidth [" + channel[0] + "] rate [" + channel[1] + "]");
+        }
+    }
+
+    /**
+     * The noise thresholds reference a 12.5 kHz channel at 25 kHz, so that channel must not be rescaled.
+     */
+    @Test
+    void referenceChannelIsNotRescaled()
+    {
+        float[] filter = ChannelFilterDesigner.design(25000.0, 12500.0);
+        assertEquals(0.298f, NoiseSquelch.getNoiseVariance(25000.0, filter), 0.01f);
+    }
+
+    /**
+     * Processes an FM tone in noise, or noise only, through the channel filter, demodulator and noise squelch.
+     * @param snr of the signal in the channel bandwidth in dB, or null for noise only.
+     * @return fraction of the audio samples passed by the squelch
+     */
+    private static double process(double bandwidth, double sampleRate, Double snr)
+    {
+        Random random = new Random(2);
+        int length = (int)(sampleRate * SECONDS);
+        float[] i = new float[length];
+        float[] q = new float[length];
+        double amplitude = snr == null ? 0.0 :
+            Math.sqrt(2.0 * NOISE_LEVEL * NOISE_LEVEL * (bandwidth / sampleRate) * Math.pow(10.0, snr / 10.0));
+        double phase = 0.0;
+
+        for(int x = 0; x < length; x++)
+        {
+            phase += 2.0 * Math.PI * (bandwidth * .2) * Math.sin(2.0 * Math.PI * 1000.0 * x / sampleRate) / sampleRate;
+            i[x] = (float)(random.nextGaussian() * NOISE_LEVEL + amplitude * Math.cos(phase));
+            q[x] = (float)(random.nextGaussian() * NOISE_LEVEL + amplitude * Math.sin(phase));
+        }
+
+        float[] coefficients = ChannelFilterDesigner.design(sampleRate, bandwidth);
+        RealFIRFilter iFilter = new RealFIRFilter(coefficients.clone());
+        RealFIRFilter qFilter = new RealFIRFilter(coefficients.clone());
+        ScalarFMDemodulator demodulator = new ScalarFMDemodulator();
+        NoiseSquelch squelch = new NoiseSquelch(NoiseSquelch.DEFAULT_NOISE_OPEN_THRESHOLD,
+                NoiseSquelch.DEFAULT_NOISE_CLOSE_THRESHOLD, NoiseSquelch.DEFAULT_HYSTERESIS_OPEN_THRESHOLD,
+                NoiseSquelch.DEFAULT_HYSTERESIS_CLOSE_THRESHOLD);
+        squelch.setSampleRate(sampleRate, coefficients);
+
+        long[] passed = {0};
+        squelch.setAudioListener(audio -> {
+            for(float sample: audio)
+            {
+                if(sample != 0.0f)
+                {
+                    passed[0]++;
+                }
+            }
+        });
+
+        for(int offset = 0; offset + BUFFER_SIZE <= length; offset += BUFFER_SIZE)
+        {
+            squelch.process(demodulator.demodulate(iFilter.filter(Arrays.copyOfRange(i, offset, offset + BUFFER_SIZE)),
+                    qFilter.filter(Arrays.copyOfRange(q, offset, offset + BUFFER_SIZE))));
+        }
+
+        return (double)passed[0] / length;
+    }
+}

src/test/java/io/github/dsheirer/dsp/squelch/VoiceModulationDetectorTest.java

@@ -0,0 +1,86 @@
+/*
+ * *****************************************************************************
+ * Copyright (C) 2014-2026 Dennis Sheirer
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program.  If not, see <http://www.gnu.org/licenses/>
+ * ****************************************************************************
+ */
+package io.github.dsheirer.dsp.squelch;
+
+import static org.junit.jupiter.api.Assertions.assertFalse;
+import static org.junit.jupiter.api.Assertions.assertTrue;
+
+import java.util.Random;
+import org.junit.jupiter.api.Test;
+
+/**
+ * Unit tests for the voice modulation detector
+ */
+class VoiceModulationDetectorTest
+{
+    private static final double[] BANDWIDTHS = {3000.0, 5000.0, 6000.0, 8333.0, 15000.0, 25000.0};
+
+    /**
+     * Fills the detector with a carrier having white envelope noise and optional modulation.
+     */
+    private static boolean analyze(double sampleRate, double bandwidth, double modulation, Random random)
+    {
+        int samples = (int)(sampleRate / 2.0);
+        VoiceModulationDetector detector = new VoiceModulationDetector(sampleRate, bandwidth, samples);
+
+        for(int x = 0; x < samples; x++)
+        {
+            double time = x / sampleRate;
+            detector.receive((float)(1.0 + modulation * Math.cos(2.0 * Math.PI * 450.0 * time) + 0.1 * random.nextGaussian()));
+        }
+
+        return detector.analyze();
+    }
+
+    @Test
+    void flatEnvelopeNoiseIsNotVoice()
+    {
+        Random random = new Random(1);
+
+        for(double bandwidth: BANDWIDTHS)
+        {
+            for(double sampleRate: new double[]{25000.0, 39062.5, 50000.0})
+            {
+                for(int x = 0; x < 50; x++)
+                {
+                    assertFalse(analyze(sampleRate, bandwidth, 0.0, random), "Bandwidth " + bandwidth);
+                }
+            }
+        }
+    }
+
+    @Test
+    void lowFrequencyModulationIsVoice()
+    {
+        Random random = new Random(2);
+
+        for(double bandwidth: BANDWIDTHS)
+        {
+            assertTrue(analyze(39062.5, bandwidth, 0.2, random), "Bandwidth " + bandwidth);
+        }
+    }
+
+    @Test
+    void partialBufferIsNotAnalyzed()
+    {
+        VoiceModulationDetector detector = new VoiceModulationDetector(25000.0, 6000.0, 12500);
+        detector.receive(1.0f);
+        assertFalse(detector.analyze());
+    }
+}

src/test/java/io/github/dsheirer/module/decode/am/AMDecoderSampleRateTest.java

@@ -0,0 +1,136 @@
+/*
+ * *****************************************************************************
+ * Copyright (C) 2014-2026 Dennis Sheirer
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program.  If not, see <http://www.gnu.org/licenses/>
+ * ****************************************************************************
+ */
+package io.github.dsheirer.module.decode.am;
+
+import static org.junit.jupiter.api.Assertions.assertEquals;
+import static org.junit.jupiter.api.Assertions.assertThrows;
+import static org.junit.jupiter.api.Assertions.assertTrue;
+
+import io.github.dsheirer.dsp.filter.decimate.DecimationFilterFactory;
+import io.github.dsheirer.module.decode.analog.DecodeConfigAnalog.Bandwidth;
+import io.github.dsheirer.sample.complex.ComplexSamples;
+import io.github.dsheirer.source.SourceEvent;
+import io.github.dsheirer.source.tuner.channel.ChannelSpecification;
+import java.util.ArrayList;
+import java.util.List;
+import org.junit.jupiter.api.Test;
+
+/**
+ * Unit tests for the channel sample rates supported by the AM decoder.
+ */
+class AMDecoderSampleRateTest
+{
+    private static final int BUFFER = 2048;
+
+    private static AMDecoder decoder(Bandwidth bandwidth, double sampleRate)
+    {
+        DecodeConfigAM config = new DecodeConfigAM();
+        config.setBandwidth(bandwidth);
+        AMDecoder decoder = new AMDecoder(config);
+        decoder.getSourceEventListener().receive(SourceEvent.sampleRateChange(sampleRate));
+        return decoder;
+    }
+
+    @Test
+    void defaultBandwidthIsSixKilohertz()
+    {
+        assertEquals(Bandwidth.BW_6_0, new DecodeConfigAM().getBandwidth());
+        assertTrue(Bandwidth.BW_6_0.isAM());
+    }
+
+    @Test
+    void minimumChannelSampleRateIsAtLeastTwiceTheBandwidth()
+    {
+        for(Bandwidth bandwidth: Bandwidth.AM_BANDWIDTHS)
+        {
+            DecodeConfigAM config = new DecodeConfigAM();
+            config.setBandwidth(bandwidth);
+            assertTrue(config.getChannelSpecification().getMinimumSampleRate() >= 2.0 * bandwidth.getValue(), bandwidth.name());
+        }
+    }
+
+    /**
+     * Follows the heterodyne channel source decimation selection for tuner sample rates, including 1.8 and 3.6 MHz which
+     * previously produced an unsupported 28,125 Hz sample rate for the default 15 kHz bandwidth.
+     */
+    @Test
+    void heterodyneChannelRatesAreSupported()
+    {
+        double[] tunerRates = {1.8E6, 2.0E6, 2.4E6, 2.56E6, 3.0E6, 3.2E6, 3.6E6, 6.0E6, 7.2E6, 8.0E6, 10.0E6, 20.0E6};
+
+        for(Bandwidth bandwidth: Bandwidth.AM_BANDWIDTHS)
+        {
+            DecodeConfigAM config = new DecodeConfigAM();
+            config.setBandwidth(bandwidth);
+            ChannelSpecification specification = config.getChannelSpecification();
+
+            for(double tunerRate: tunerRates)
+            {
+                int decimation = DecimationFilterFactory.getDecimationRate((int)(tunerRate / specification.getMinimumSampleRate()));
+                decoder(bandwidth, tunerRate / decimation);
+            }
+        }
+    }
+
+    /**
+     * Polyphase channel rates don't use the channel specification minimum rate.
+     */
+    @Test
+    void ratesBelowTwiceTheBandwidthDecodeAudio()
+    {
+        for(double sampleRate: new double[]{25000.0, 28125.0})
+        {
+            AMDecoder decoder = decoder(Bandwidth.BW_15_0, sampleRate);
+            List<float[]> audio = new ArrayList<>();
+            decoder.setBufferListener(audio::add);
+            int sample = 0;
+
+            for(int b = 0; b < (int)(sampleRate * 2.0 / BUFFER); b++)
+            {
+                float[] i = new float[BUFFER];
+                float[] q = new float[BUFFER];
+
+                for(int x = 0; x < BUFFER; x++)
+                {
+                    i[x] = 0.01f * (1.0f + 0.8f * (float)Math.cos(2.0 * Math.PI * 1000.0 * sample++ / sampleRate));
+                }
+
+                decoder.receive(new ComplexSamples(i, q, 0L));
+            }
+
+            float peak = 0.0f;
+
+            for(float[] buffer: audio.subList(audio.size() / 2, audio.size()))
+            {
+                for(float value: buffer)
+                {
+                    peak = Math.max(peak, Math.abs(value));
+                }
+            }
+
+            assertEquals(0.6f, peak, 0.05f, "Peak at sample rate " + sampleRate);
+        }
+    }
+
+    @Test
+    void rateBelowTheBandwidthIsRejected()
+    {
+        assertThrows(IllegalStateException.class, () -> decoder(Bandwidth.BW_25_0, 20000.0));
+    }
+}

src/test/java/io/github/dsheirer/module/decode/am/AMDecoderSquelchRequestTest.java

@@ -0,0 +1,63 @@
+/*
+ * *****************************************************************************
+ * Copyright (C) 2014-2026 Dennis Sheirer
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program.  If not, see <http://www.gnu.org/licenses/>
+ * ****************************************************************************
+ */
+package io.github.dsheirer.module.decode.am;
+
+import static org.junit.jupiter.api.Assertions.assertEquals;
+
+import io.github.dsheirer.source.SourceEvent;
+import java.util.ArrayList;
+import java.util.List;
+import org.junit.jupiter.api.Test;
+
+/**
+ * Unit tests for the source event requests that the squelch controls use to get the current squelch settings.
+ */
+class AMDecoderSquelchRequestTest
+{
+    private static List<SourceEvent> events(DecodeConfigAM config, SourceEvent request)
+    {
+        AMDecoder decoder = new AMDecoder(config);
+        List<SourceEvent> events = new ArrayList<>();
+        decoder.setSourceEventListener(events::add);
+        decoder.getSourceEventListener().receive(request);
+        return events;
+    }
+
+    @Test
+    void currentThresholdRequestIsAnswered()
+    {
+        DecodeConfigAM config = new DecodeConfigAM();
+        config.setSquelchThreshold(-70);
+        List<SourceEvent> events = events(config, SourceEvent.requestCurrentSquelchThreshold());
+        assertEquals(1, events.size());
+        assertEquals(SourceEvent.Event.NOTIFICATION_SQUELCH_THRESHOLD, events.getFirst().getEvent());
+        assertEquals(-70.0, events.getFirst().getValue().doubleValue(), 0.01);
+    }
+
+    @Test
+    void currentAutoTrackRequestIsAnswered()
+    {
+        DecodeConfigAM config = new DecodeConfigAM();
+        config.setSquelchAutoTrack(false);
+        List<SourceEvent> events = events(config, SourceEvent.requestCurrentSquelchAutoTrack());
+        assertEquals(1, events.size());
+        assertEquals(SourceEvent.Event.NOTIFICATION_SQUELCH_AUTO_TRACK, events.getFirst().getEvent());
+        assertEquals(0, events.getFirst().getValue().intValue());
+    }
+}

src/test/java/io/github/dsheirer/module/decode/p25/phase1/P25P1DecoderLSMTest.java

@@ -278,7 +278,7 @@ public class P25P1DecoderLSMTest
     /**
      * Adds the CRC-CCITT checksum, 1/2 rate trellis encodes and interleaves the TSBK into 98 dibits.
      */
-    private static List<Dibit> encodeTSBK(BitSet tsbk)
+    static List<Dibit> encodeTSBK(BitSet tsbk)
     {
         BitSet message = (BitSet)tsbk.clone();
         int checksum = 0xFFFF;
@@ -387,7 +387,7 @@ public class P25P1DecoderLSMTest
     /**
      * Adds the most significant bits first, as dibits.
      */
-    private static void addBits(List<Dibit> dibits, long value, int bitCount)
+    static void addBits(List<Dibit> dibits, long value, int bitCount)
     {
         for(int bit = bitCount - 2; bit >= 0; bit -= 2)
         {
@@ -398,7 +398,7 @@ public class P25P1DecoderLSMTest
     /**
      * Sets the value at the bit offset, most significant bit first.
      */
-    private static void setValue(BitSet bits, int offset, int bitCount, int value)
+    static void setValue(BitSet bits, int offset, int bitCount, int value)
     {
         for(int x = 0; x < bitCount; x++)
         {

src/test/java/io/github/dsheirer/module/decode/p25/phase1/P25P1MessageFramerTest.java

@@ -0,0 +1,238 @@
+/*
+ * *****************************************************************************
+ * Copyright (C) 2014-2026 Dennis Sheirer
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program.  If not, see <http://www.gnu.org/licenses/>
+ * ****************************************************************************
+ */
+
+package io.github.dsheirer.module.decode.p25.phase1;
+
+import io.github.dsheirer.dsp.symbol.Dibit;
+import io.github.dsheirer.edac.bch.BCH_63_16_23_P25;
+import io.github.dsheirer.message.IMessage;
+import io.github.dsheirer.module.decode.p25.phase1.message.tsbk.TSBKMessage;
+import io.github.dsheirer.module.decode.p25.phase1.sync.P25P1SyncDetector;
+import java.util.ArrayList;
+import java.util.BitSet;
+import java.util.Collections;
+import java.util.List;
+import java.util.Random;
+import org.junit.jupiter.api.Test;
+
+import static org.junit.jupiter.api.Assertions.assertEquals;
+
+/**
+ * JUnit tests for the P25 Phase 1 message framer recovery from a frame with a failed NID.  The failed frame assembles
+ * as a place holder and the valid NID of the next frame forces completion of that place holder, which must not impact
+ * assembly of the next frame.
+ */
+public class P25P1MessageFramerTest
+{
+    private static final int NAC = 0x293;
+    private static final int TSBK_DUID = 7;
+    private static final int OPCODE_RFSS_STATUS_BROADCAST = 58;
+    private static final int PDU_FORMAT_AMBTC = 23;
+    private static final int FRAME_DIBITS = 180; //Sync, NID, header/single TSBK, status dibits and null padding
+    private static final int DATA_BLOCK_DIBITS = 108; //98 dibits, 3 status dibits and null padding, to next frame
+    private static final int SYNC_DIBITS = 24;
+    private static final int SYNC_FRAMES = 8; //Valid frames preceding the failed frame so that the NAC is tracked
+    private static final int NEXT_FRAMES = 3; //Valid frames following the failed frame
+
+    private final Random mRandom = new Random(1);
+
+    /**
+     * Test: control case with all frames detected.
+     */
+    @Test
+    void testNoFailedFrame()
+    {
+        assertEquals(SYNC_FRAMES + NEXT_FRAMES, process(Collections.emptyList()));
+    }
+
+    /**
+     * Test: a missed AMBTC PDU, fully assembled as a place holder, dispatches all of its data blocks without the
+     * 'message under assembly is full' error and without losing the next frame, for each supported block count.
+     */
+    @Test
+    void testPlaceHolderResolvedAsPDU()
+    {
+        for(int blocks = 1; blocks <= 5; blocks++)
+        {
+            assertEquals(SYNC_FRAMES + NEXT_FRAMES, process(getPDU(blocks, blocks)), blocks + " data blocks");
+        }
+    }
+
+    /**
+     * Test: a missed AMBTC PDU that's truncated by the next frame, where the header indicates more data blocks than
+     * were assembled, doesn't capture the next frame as data blocks.
+     */
+    @Test
+    void testPlaceHolderResolvedAsTruncatedPDU()
+    {
+        assertEquals(SYNC_FRAMES + NEXT_FRAMES, process(getPDU(3, 1)));
+    }
+
+    /**
+     * Test: a missed corrupt TSBK, where the failed CRC can't indicate the last block, doesn't capture the next frame
+     * as the second TSBK of the sequence.
+     */
+    @Test
+    void testPlaceHolderResolvedAsCorruptTSBK()
+    {
+        List<Dibit> noise = new ArrayList<>();
+
+        for(int x = 0; x < FRAME_DIBITS; x++)
+        {
+            noise.add(Dibit.values()[mRandom.nextInt(4)]);
+        }
+
+        assertEquals(SYNC_FRAMES + NEXT_FRAMES, process(noise));
+    }
+
+    /**
+     * Processes valid TSBK frames, the frame that fails sync detection, and then more valid TSBK frames.
+     * @param failedFrame dibits
+     * @return count of valid TSBK messages dispatched by the framer.
+     */
+    private int process(List<Dibit> failedFrame)
+    {
+        int[] validCount = new int[1];
+        P25P1MessageFramer framer = new P25P1MessageFramer();
+        framer.setListener((IMessage message) -> {
+            if(message instanceof TSBKMessage tsbk && tsbk.isValid())
+            {
+                validCount[0]++;
+            }
+        });
+        framer.start();
+
+        for(int x = 0; x < SYNC_FRAMES; x++)
+        {
+            process(framer, getFrame(TSBK_DUID, getTSBK(), FRAME_DIBITS), true);
+        }
+
+        process(framer, failedFrame, false);
+
+        for(int x = 0; x < NEXT_FRAMES; x++)
+        {
+            process(framer, getFrame(TSBK_DUID, getTSBK(), FRAME_DIBITS), true);
+        }
+
+        //A message is dispatched on the dibit following the message, so flush the final frame
+        process(framer, Collections.nCopies(FRAME_DIBITS, Dibit.D00_PLUS_1), false);
+
+        return validCount[0];
+    }
+
+    /**
+     * Processes the frame dibits, optionally indicating a sync detection after the final sync pattern dibit.
+     */
+    private static void process(P25P1MessageFramer framer, List<Dibit> dibits, boolean detectSync)
+    {
+        for(int x = 0; x < dibits.size(); x++)
+        {
+            framer.process(dibits.get(x));
+
+            if(detectSync && x == SYNC_DIBITS - 1)
+            {
+                framer.syncDetected();
+            }
+        }
+    }
+
+    /**
+     * Creates a single block TSBK with the last block indicator set.
+     */
+    private BitSet getTSBK()
+    {
+        BitSet tsbk = new BitSet();
+        tsbk.set(0);
+        P25P1DecoderLSMTest.setValue(tsbk, 2, 6, OPCODE_RFSS_STATUS_BROADCAST);
+
+        for(int x = 16; x < 80; x++)
+        {
+            tsbk.set(x, mRandom.nextBoolean());
+        }
+
+        return tsbk;
+    }
+
+    /**
+     * Creates an AMBTC PDU frame.
+     * @param indicatedBlocks count of blocks to follow in the header
+     * @param actualBlocks count of data blocks in the frame.
+     */
+    private List<Dibit> getPDU(int indicatedBlocks, int actualBlocks)
+    {
+        BitSet header = new BitSet();
+        header.set(2); //Outbound
+        P25P1DecoderLSMTest.setValue(header, 3, 5, PDU_FORMAT_AMBTC);
+        P25P1DecoderLSMTest.setValue(header, 49, 7, indicatedBlocks);
+
+        List<Dibit> data = getData(header);
+
+        for(int x = 0; x < actualBlocks; x++)
+        {
+            data.addAll(P25P1DecoderLSMTest.encodeTSBK(getTSBK()));
+        }
+
+        return addStatusDibits(data, FRAME_DIBITS + actualBlocks * DATA_BLOCK_DIBITS);
+    }
+
+    /**
+     * Creates a frame with the sync, NID, and encoded message.
+     */
+    private static List<Dibit> getFrame(int duid, BitSet message, int length)
+    {
+        return addStatusDibits(getData(duid, message), length);
+    }
+
+    private static List<Dibit> getData(BitSet pduHeader)
+    {
+        return getData(12, pduHeader);
+    }
+
+    private static List<Dibit> getData(int duid, BitSet message)
+    {
+        List<Dibit> data = new ArrayList<>();
+        P25P1DecoderLSMTest.addBits(data, P25P1SyncDetector.SYNC_PATTERN, 48);
+        P25P1DecoderLSMTest.addBits(data, BCH_63_16_23_P25.encode(NAC, duid) << 1, 64); //64th (parity) bit is zero
+        data.addAll(P25P1DecoderLSMTest.encodeTSBK(message));
+        return data;
+    }
+
+    /**
+     * Inserts a status dibit at every 36th dibit and null pads the frame to the length.
+     */
+    private static List<Dibit> addStatusDibits(List<Dibit> data, int length)
+    {
+        List<Dibit> frame = new ArrayList<>();
+        int pointer = 0;
+
+        for(int x = 1; x <= length; x++)
+        {
+            if(x % 36 == 0)
+            {
+                frame.add(Dibit.D01_PLUS_3); //Outbound (repeater) status
+            }
+            else
+            {
+                frame.add(pointer < data.size() ? data.get(pointer++) : Dibit.D00_PLUS_1);
+            }
+        }
+
+        return frame;
+    }
+}

src/test/java/org/jtransforms/fft/ReusableFloatInverseFFTTest.java

@@ -0,0 +1,134 @@
+/*
+ * *****************************************************************************
+ * Copyright (C) 2014-2026 Dennis Sheirer
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program.  If not, see <http://www.gnu.org/licenses/>
+ * ****************************************************************************
+ */
+package org.jtransforms.fft;
+
+import static org.junit.jupiter.api.Assertions.assertArrayEquals;
+import static org.junit.jupiter.api.Assertions.assertEquals;
+
+import java.lang.management.ManagementFactory;
+import java.util.Random;
+import org.junit.jupiter.api.Test;
+
+/**
+ * Tests that the reusable inverse FFT is an exact replacement for FloatFFT_1D.
+ */
+class ReusableFloatInverseFFTTest
+{
+    private static final int OFFSET = 6;
+    private static final int LARGEST_SIZE = 5000;
+
+    private static float[] noise(int length, Random random)
+    {
+        float[] samples = new float[length];
+
+        for(int x = 0; x < length; x++)
+        {
+            samples[x] = random.nextFloat() * 2.0f - 1.0f;
+        }
+
+        return samples;
+    }
+
+    /**
+     * Test: output values are bit-identical to FloatFFT_1D for every size, including powers of two and sizes with other
+     * prime factors, and samples outside of the block aren't changed.  Each instance is used twice to show that
+     * scratch contents don't carry over between calls.
+     */
+    @Test
+    void matchesFloatFFT1D()
+    {
+        Random random = new Random(0xC0FFEEL);
+
+        for(int size = 1; size <= LARGEST_SIZE; size += size < 512 ? 1 : 53)
+        {
+            ReusableFloatInverseFFT reusable = new ReusableFloatInverseFFT(size);
+            FloatFFT_1D reference = new FloatFFT_1D(size);
+
+            for(int pass = 0; pass < 2; pass++)
+            {
+                float[] expected = noise(2 * size + 2 * OFFSET, random);
+                float[] actual = expected.clone();
+                reference.complexInverse(expected, OFFSET, true);
+                reusable.complexInverse(actual, OFFSET);
+                assertArrayEquals(expected, actual, 0.0f, "Size " + size);
+            }
+        }
+    }
+
+    /**
+     * Test: every channel count from 2 to 4800 with only factors of 2, 3 and 5 matches FloatFFT_1D.  These are the only
+     * sizes the channelizer can select.
+     */
+    @Test
+    void matchesFloatFFT1DForChannelizerSizes()
+    {
+        Random random = new Random(0xBEEFL);
+
+        for(int size = 2; size <= 4800; size += 2)
+        {
+            int remaining = size;
+
+            for(int factor : new int[]{2, 3, 5})
+            {
+                while(remaining % factor == 0)
+                {
+                    remaining /= factor;
+                }
+            }
+
+            if(remaining == 1)
+            {
+                float[] expected = noise(2 * size, random);
+                float[] actual = expected.clone();
+                new FloatFFT_1D(size).complexInverse(expected, 0, true);
+                new ReusableFloatInverseFFT(size).complexInverse(actual, 0);
+                assertArrayEquals(expected, actual, 0.0f, "Size " + size);
+            }
+        }
+    }
+
+    /**
+     * Test: transforms don't allocate, for a mixed-radix size with an odd pass count and an even pass count.
+     */
+    @Test
+    void doesNotAllocate()
+    {
+        com.sun.management.ThreadMXBean threads = (com.sun.management.ThreadMXBean)ManagementFactory.getThreadMXBean();
+        long threadId = Thread.currentThread().threadId();
+
+        for(int size : new int[]{96, 400})
+        {
+            ReusableFloatInverseFFT fft = new ReusableFloatInverseFFT(size);
+            float[] samples = noise(2 * size, new Random(1L));
+            fft.complexInverse(samples, 0);
+
+            long before = threads.getThreadAllocatedBytes(threadId);
+
+            for(int x = 0; x < 1000; x++)
+            {
+                fft.complexInverse(samples, 0);
+            }
+
+            long allocated = threads.getThreadAllocatedBytes(threadId) - before;
+
+            //FloatFFT_1D would allocate at least 8 bytes per channel, per call.  Allow for measurement overhead.
+            assertEquals(0, allocated / (1000L * size), "Size " + size + " allocated " + allocated + " bytes");
+        }
+    }
+}