NBFM Channel level CTCSS/DCS and audio features (#2425)

NBFM decoder enhancements.  CTCSS and DCS squelch control.  Adds deemphasis, high pass filter control, and auto-level control

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

@@ -24,7 +24,7 @@ import org.apache.commons.math3.util.FastMath;
 /**
  * Implements the Goertzel Filter as described in
  * http://en.wikipedia.org/wiki/Goertzel_algorithm
- * <p>
+ *
  * Calculates the magnitude of a specific frequency component within a window of
  * samples, using a Goertzel Filter (ie an optimized DFT).
  */
@@ -101,9 +101,10 @@ public class GoertzelFilter
         //power = s_prev2 * s_prev2 + s_prev * s_prev - coeff * s_prev * s_prev2 ;
 
         double magnitude = (s_prev2 * s_prev2) + (s_prev * s_prev) - (mCoefficient * s_prev * s_prev2);
-        int binZero = getBinZeroPower(samples);
-
-        int power = (int)(20 * FastMath.log10(magnitude / binZero));
+        // Removed because bin(0) is likely to be (int) zero on audio samples
+        //int binZero = getBinZeroPower(samples);
+        //int power = (int)(20 * FastMath.log10(magnitude / binZero));
+        int power = (int)(20 * FastMath.log10(magnitude));
 
         return power;
     }
@@ -119,7 +120,6 @@ public class GoertzelFilter
         {
             retVal += sample;
         }
-
         return retVal;
     }
 

src/main/java/io/github/dsheirer/dsp/filter/iir/DeemphasisFilter.java

@@ -15,15 +15,22 @@
  ******************************************************************************/
 package io.github.dsheirer.dsp.filter.iir;
 
+import io.github.dsheirer.audio.AbstractAudioFilter;
 import org.apache.commons.math3.util.FastMath;
 
-public class DeemphasisFilter
+public class DeemphasisFilter extends AbstractAudioFilter
 {
 	private static final float MAX_SAMPLE_VALUE = 0.95f;
 	private float mAlpha;
 	private float mGain;
 	private float mPrevious = 0.0f;
-	
+
+    /**
+     * Create an instance
+     * @param sampleRate - usually 8000 Hz
+     * @param cutoff - cutoff frequency
+     * @param gain - gain (linear)
+     */
 	public DeemphasisFilter( float sampleRate, float cutoff, float gain )
 	{
 		mAlpha = (float)FastMath.exp( -2.0 * FastMath.PI * cutoff * ( 1.0 / sampleRate ) );
@@ -45,7 +52,7 @@ public class DeemphasisFilter
 		}
 		else return FastMath.max(value, -MAX_SAMPLE_VALUE);
 	}
-	
+	@Override
 	public float[] filter( float[] samples )
 	{
 		for( int x = 0; x < samples.length; x++ )

src/main/java/io/github/dsheirer/dsp/gain/AudioGainAndDcFilter.java

@@ -1,6 +1,6 @@
 /*
  * *****************************************************************************
- * Copyright (C) 2014-2023 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
@@ -47,6 +47,7 @@ public class AudioGainAndDcFilter
     private float mObjectiveGain;
     private float mObjectiveAmplitude;
     private float mMaxObservedAmplitude;
+    private float mPercentDecayRate = 10f;
 
     /**
      * Constructs an instance
@@ -82,8 +83,9 @@ public class AudioGainAndDcFilter
         float currentAmplitude;
         float dcAccumulator = 0.0f;
 
-        //Decay the max observed value by 10% each buffer so that an initial spike doesn't carry across all buffers
-        mMaxObservedAmplitude *= 0.9f;
+        //Decay the max observed value by a specified percentage each buffer so that an initial
+        // spike doesn't carry across all buffers
+        mMaxObservedAmplitude *= ((100 - mPercentDecayRate )/ 100);
 
         for(float sample: samples)
         {
@@ -133,7 +135,17 @@ public class AudioGainAndDcFilter
         }
 
         mCurrentGain = gain;
+        //mLog.debug("Gain: {}", gain);
         mObjectiveGain = objective;
         return processed;
     }
+
+    /**
+     * Overrides the default decay rate of 10 %.
+     * @param newRate specified as a percentage (i.e. 2 equals 2%)
+     */
+    public void setDecayRate(float newRate)
+    {
+        mPercentDecayRate = newRate;
+    }
 }