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());
+    }
 }