Resolves 1122. Adds decimation to NBFMDecoder so that channel bandwidth is reduced to min sample rate needed. This reduces the impact on channel power measurement from adjacent channels. (#1129)

Co-authored-by: Dennis Sheirer <dsheirer@github.com>

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

@@ -1,7 +1,6 @@
 /*
- * ******************************************************************************
- * sdrtrunk
- * Copyright (C) 2014-2018 Dennis Sheirer
+ * *****************************************************************************
+ * Copyright (C) 2014-2022 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
@@ -15,7 +14,7 @@
  *
  * 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.channelizer;
 
@@ -40,6 +39,7 @@ public class PolyphaseChannelSource extends TunerChannelSource
 {
 //    private final static Logger mLog = LoggerFactory.getLogger(PolyphaseChannelSource.class);
 
+    private static final int PROCESSED_BUFFER_SAMPLE_SIZE = 2048;
     private ReusableComplexBufferAssembler mReusableComplexBufferAssembler;
     private IPolyphaseChannelOutputProcessor mPolyphaseChannelOutputProcessor;
     private IPolyphaseChannelOutputProcessor mReplacementPolyphaseChannelOutputProcessor;
@@ -71,7 +71,7 @@ public class PolyphaseChannelSource extends TunerChannelSource
         super(producerSourceEventListener, tunerChannel);
         mPolyphaseChannelOutputProcessor = outputProcessor;
         mChannelSampleRate = channelSampleRate;
-        mReusableComplexBufferAssembler = new ReusableComplexBufferAssembler(2500, mChannelSampleRate);
+        mReusableComplexBufferAssembler = new ReusableComplexBufferAssembler(PROCESSED_BUFFER_SAMPLE_SIZE, mChannelSampleRate);
 
         float[] filterCoefficients = getLowPassFilter(channelSampleRate, channelSpecification.getPassFrequency(),
             channelSpecification.getStopFrequency());

src/main/java/io/github/dsheirer/dsp/filter/decimate/ComplexDecimateX0Filter.java

@@ -0,0 +1,40 @@
+/*
+ * *****************************************************************************
+ * Copyright (C) 2014-2022 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.decimate;
+
+import io.github.dsheirer.sample.buffer.ReusableComplexBuffer;
+
+/**
+ * No decimation filter.
+ */
+public class ComplexDecimateX0Filter implements IComplexDecimationFilter
+{
+    @Override
+    public float[] decimateComplex(float[] samples)
+    {
+        return samples;
+    }
+
+    @Override
+    public ReusableComplexBuffer decimate(ReusableComplexBuffer buffer)
+    {
+        return buffer;
+    }
+}

src/main/java/io/github/dsheirer/dsp/filter/decimate/DecimationFilterFactory.java

@@ -1,6 +1,6 @@
 /*
  * *****************************************************************************
- * Copyright (C) 2014-2021 Dennis Sheirer
+ * Copyright (C) 2014-2022 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
@@ -24,7 +24,7 @@ package io.github.dsheirer.dsp.filter.decimate;
  */
 public class DecimationFilterFactory
 {
-    private static final int[] SUPPORTED_RATES = new int[]{2,4,8,16,32,64,128,256,512,1024};
+    private static final int[] SUPPORTED_RATES = new int[]{0,2,4,8,16,32,64,128,256,512,1024};
 
     /**
      * Creates a real-valued decimation filter for float array sample buffers providing greater than 100 dB of
@@ -37,6 +37,8 @@ public class DecimationFilterFactory
     {
         switch(decimationRate)
         {
+            case 0:
+                return new RealDecimateX0Filter();
             case 2:
                 return new RealDecimateX2Filter();
             case 4:
@@ -74,6 +76,8 @@ public class DecimationFilterFactory
     {
         switch(decimationRate)
         {
+            case 0:
+                return new ComplexDecimateX0Filter();
             case 2:
                 return new ComplexDecimateX2Filter();
             case 4:

src/main/java/io/github/dsheirer/dsp/filter/decimate/IComplexDecimationFilter.java

@@ -1,6 +1,6 @@
 /*
  * *****************************************************************************
- * Copyright (C) 2014-2021 Dennis Sheirer
+ * Copyright (C) 2014-2022 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
@@ -19,10 +19,24 @@
 
 package io.github.dsheirer.dsp.filter.decimate;
 
+import io.github.dsheirer.sample.buffer.ReusableComplexBuffer;
+
 /**
  * Interface for a decimation filter for float array sample buffers
  */
 public interface IComplexDecimationFilter
 {
+    /**
+     * Decimates an array of float complex samples
+     * @param samples to decimate
+     * @return decimated samples
+     */
     float[] decimateComplex(float[] samples);
+
+    /**
+     * Decimates an buffer of float complex samples
+     * @param buffer to decimate
+     * @return decimated samples
+     */
+    ReusableComplexBuffer decimate(ReusableComplexBuffer buffer);
 }

src/main/java/io/github/dsheirer/dsp/filter/decimate/RealDecimateX0Filter.java

@@ -0,0 +1,32 @@
+/*
+ * *****************************************************************************
+ * Copyright (C) 2014-2022 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.decimate;
+
+/**
+ * No decimation filter.
+ */
+public class RealDecimateX0Filter implements IRealDecimationFilter
+{
+    @Override
+    public float[] decimateReal(float[] samples)
+    {
+        return samples;
+    }
+}

src/main/java/io/github/dsheirer/dsp/filter/halfband/complex/ComplexHalfBandDecimationFilter.java

@@ -1,6 +1,6 @@
 /*
  * *****************************************************************************
- * Copyright (C) 2014-2021 Dennis Sheirer
+ * Copyright (C) 2014-2022 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
@@ -20,6 +20,8 @@
 package io.github.dsheirer.dsp.filter.halfband.complex;
 
 import io.github.dsheirer.dsp.filter.decimate.IComplexDecimationFilter;
+import io.github.dsheirer.sample.buffer.ReusableComplexBuffer;
+import io.github.dsheirer.sample.buffer.ReusableComplexBufferQueue;
 
 /**
  * Complex half-band filter that processes samples on a per-array basis, versus a per-sample basis.
@@ -35,6 +37,7 @@ public class ComplexHalfBandDecimationFilter implements IComplexDecimationFilter
     private int mCoefficientsLengthMinus2;
     private int mBufferPointer;
     private int mHalf;
+    private ReusableComplexBufferQueue mReusableComplexBufferQueue = new ReusableComplexBufferQueue("half-band decimation filter");
 
     /**
      * Constructs a complex sample half-band decimate x2 filter using the specified filter coefficients.
@@ -118,4 +121,17 @@ public class ComplexHalfBandDecimationFilter implements IComplexDecimationFilter
 
         return filtered;
     }
+
+    /**
+     * Decimates the complex samples and returns a buffer of decimated samples.
+     * @param buffer to decimate
+     * @return decimated buffer.
+     */
+    @Override
+    public ReusableComplexBuffer decimate(ReusableComplexBuffer buffer)
+    {
+        float[] decimated = decimateComplex(buffer.getSamples());
+        buffer.decrementUserCount();
+        return mReusableComplexBufferQueue.getBuffer(decimated, buffer.getTimestamp());
+    }
 }

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

@@ -1,20 +1,21 @@
-/*******************************************************************************
- *     SDR Trunk 
- *     Copyright (C) 2014,2015 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/>
- ******************************************************************************/
+/*
+ * *****************************************************************************
+ * Copyright (C) 2014-2022 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.nbfm;
 
 import io.github.dsheirer.channel.state.DecoderStateEvent;
@@ -22,6 +23,8 @@ import io.github.dsheirer.channel.state.IDecoderStateEventProvider;
 import io.github.dsheirer.channel.state.State;
 import io.github.dsheirer.dsp.filter.FilterFactory;
 import io.github.dsheirer.dsp.filter.Window;
+import io.github.dsheirer.dsp.filter.decimate.DecimationFilterFactory;
+import io.github.dsheirer.dsp.filter.decimate.IComplexDecimationFilter;
 import io.github.dsheirer.dsp.filter.design.FilterDesignException;
 import io.github.dsheirer.dsp.filter.fir.FIRFilterSpecification;
 import io.github.dsheirer.dsp.filter.fir.complex.ComplexFIRFilter2;
@@ -49,11 +52,12 @@ public class NBFMDecoder extends PrimaryDecoder implements ISourceEventListener,
 {
 	private final static Logger mLog = LoggerFactory.getLogger(NBFMDecoder.class);
 	private static final double DEMODULATED_AUDIO_SAMPLE_RATE = 8000.0;
-	private static final double POWER_SQUELCH_ALPHA_DECAY = 0.0002;
+	private static final double POWER_SQUELCH_ALPHA_DECAY = 0.0004;
 	private static final double POWER_SQUELCH_THRESHOLD_DB = -78.0;
 	private static final int POWER_SQUELCH_RAMP = 4;
 
 	private ComplexFIRFilter2 mIQFilter;
+	private IComplexDecimationFilter mDecimationFilter;
 	private SquelchingFMDemodulator mDemodulator = new SquelchingFMDemodulator(POWER_SQUELCH_ALPHA_DECAY,
 			POWER_SQUELCH_THRESHOLD_DB, POWER_SQUELCH_RAMP);
 	private RealResampler mResampler;
@@ -131,7 +135,9 @@ public class NBFMDecoder extends PrimaryDecoder implements ISourceEventListener,
 					"event before it can process complex sample buffers");
 		}
 
-		ReusableComplexBuffer basebandFilteredBuffer = mIQFilter.filter(reusableComplexBuffer);
+		ReusableComplexBuffer decimatedBuffer = mDecimationFilter.decimate(reusableComplexBuffer);
+		ReusableComplexBuffer basebandFilteredBuffer = mIQFilter.filter(decimatedBuffer);
+
 		ReusableFloatBuffer demodulatedBuffer = mDemodulator.demodulate(basebandFilteredBuffer);
 
 		if(mResampler != null)
@@ -268,11 +274,31 @@ public class NBFMDecoder extends PrimaryDecoder implements ISourceEventListener,
 
 				double sampleRate = sourceEvent.getValue().doubleValue();
 
-				if((sampleRate < (2.0 * mChannelBandwidth)))
+				int decimationRate = 0;
+				double decimatedSampleRate = sampleRate;
+
+				if(sampleRate / 2 > mChannelBandwidth)
+				{
+					decimationRate = 2;
+
+					while(sampleRate / decimationRate / 2 > mChannelBandwidth)
+					{
+						decimationRate *= 2;
+					}
+				}
+
+				if(decimationRate > 0)
+				{
+					decimatedSampleRate /= decimationRate;
+				}
+
+				mDecimationFilter = DecimationFilterFactory.getComplexDecimationFilter(decimationRate);
+
+				if((decimatedSampleRate < (2.0 * mChannelBandwidth)))
 				{
 					throw new IllegalStateException("FM Demodulator with channel bandwidth [" + mChannelBandwidth +
 							"] requires a channel sample rate of [" + (2.0 * mChannelBandwidth + "] - sample rate of [" +
-							sampleRate + "] is not supported"));
+							decimatedSampleRate + "] is not supported"));
 				}
 
 				int passBandStop = (int)(mChannelBandwidth * .8);
@@ -281,7 +307,7 @@ public class NBFMDecoder extends PrimaryDecoder implements ISourceEventListener,
 				float[] filterTaps = null;
 
 				FIRFilterSpecification specification = FIRFilterSpecification.lowPassBuilder()
-						.sampleRate(sampleRate)
+						.sampleRate(decimatedSampleRate * 2)
 						.gridDensity(16)
 						.oddLength(true)
 						.passBandCutoff(passBandStop)
@@ -300,18 +326,21 @@ public class NBFMDecoder extends PrimaryDecoder implements ISourceEventListener,
 				{
 					mLog.error("Couldn't design FM demodulator remez filter for sample rate [" + sampleRate +
 							"] pass frequency [" + passBandStop + "] and stop frequency [" + stopBandStart +
-							"] - using sinc filter");
+							"] - will proceed using sinc (low-pass) filter");
 				}
 
 				if(filterTaps == null)
 				{
-					filterTaps = FilterFactory.getLowPass(sampleRate, passBandStop, stopBandStart, 60,
+					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");
+					filterTaps = FilterFactory.getLowPass(decimatedSampleRate, passBandStop, stopBandStart, 60,
 							Window.WindowType.HAMMING, true);
 				}
 
 				mIQFilter = new ComplexFIRFilter2(filterTaps);
 
-				mResampler = new RealResampler(sampleRate, mOutputSampleRate, 2000, 1000);
+				mResampler = new RealResampler(decimatedSampleRate, mOutputSampleRate, 2000, 1000);
 
 				mResampler.setListener(reusableFloatBuffer ->
 				{

src/main/java/io/github/dsheirer/sample/buffer/AbstractReusableBufferQueue.java

@@ -1,18 +1,21 @@
-/*******************************************************************************
- * sdr-trunk
- * Copyright (C) 2014-2018 Dennis Sheirer
+/*
+ * *****************************************************************************
+ * Copyright (C) 2014-2022 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 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.
+ * 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/>
- *
- ******************************************************************************/
+ * 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.sample.buffer;
 
 import org.slf4j.Logger;
@@ -50,6 +53,14 @@ public abstract class AbstractReusableBufferQueue<T extends AbstractReusableBuff
     {
     }
 
+    /**
+     * Turns on/off logging of buffer creation
+     */
+    public void setDebugLogging(boolean enabled)
+    {
+        mBufferCreationLoggingEnabled = enabled;
+    }
+
     /**
      * Disposes of any reclaimed buffers to prepare this queue for disposal.
      */

src/main/java/io/github/dsheirer/sample/buffer/ReusableComplexBufferQueue.java

@@ -1,18 +1,21 @@
-/*******************************************************************************
- * sdr-trunk
- * Copyright (C) 2014-2018 Dennis Sheirer
+/*
+ * *****************************************************************************
+ * Copyright (C) 2014-2022 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 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.
+ * 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/>
- *
- ******************************************************************************/
+ * 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.sample.buffer;
 
 import org.slf4j.Logger;
@@ -61,4 +64,31 @@ public class ReusableComplexBufferQueue extends AbstractReusableBufferQueue<Reus
 
         return buffer;
     }
+
+    /**
+     * Returns a buffer loaded with the samples.
+     * @param samples to load
+     * @param timestamp to apply
+     * @return buffer
+     */
+    public ReusableComplexBuffer getBuffer(float[] samples, long timestamp)
+    {
+        ReusableComplexBuffer buffer = getRecycledBuffer();
+
+        if(buffer == null)
+        {
+            buffer = new ReusableComplexBuffer(this, samples);
+            buffer.setTimestamp(timestamp);
+            buffer.setDebugName("Owner:" + getDebugName());
+            incrementBufferCount();
+        }
+        else
+        {
+            buffer.reloadFrom(samples, timestamp);
+        }
+
+        buffer.incrementUserCount();
+
+        return buffer;
+    }
 }