P25 - work in progress to improve CQPSK LSM audio output. Audio output is still choppy but greatly improved over the previous test release.

src/dsp/gain/ComplexFeedForwardGainControl.java

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+package dsp.gain;
+
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
+
+import sample.Listener;
+import sample.Provider;
+import sample.complex.ComplexSample;
+import buffer.FloatCircularBuffer;
+
+/*******************************************************************************
+ *     SDR Trunk 
+ *     Copyright (C) 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/>
+ *     
+ *     This class is modeled using concepts detailed in the GNURadio 
+ *     implementation of feed forward AGC class located at:
+ *     https://github.com/gnuradio/gnuradio/blob/master/gr-analog/lib/
+ *     feedforward_agc_cc_impl.cc
+ *     
+ ******************************************************************************/
+public class ComplexFeedForwardGainControl 
+		implements Listener<ComplexSample>, Provider<ComplexSample>
+{
+	private final static Logger mLog = 
+			LoggerFactory.getLogger( ComplexFeedForwardGainControl.class );
+
+	public static final float OBJECTIVE_ENVELOPE = 1.0f;
+	public static final float MINIMUM_ENVELOPE = 0.0001f;
+
+	private Listener<ComplexSample> mListener;
+
+	private FloatCircularBuffer mEnvelopeHistory;
+	
+	private float mMaxEnvelope = 0.0f;
+	private float mGain = 1.0f;
+	
+	/**
+	 * Dynamic gain control for incoming sample stream to amplify or attenuate
+	 * all samples toward an objective unity)gain, using the maximum envelope 
+	 * value detected in the stream history window.  
+	 * 
+	 * Uses the specified damping factor to limit gain swings.  Damping factor
+	 * is applied against the delta between current gain value and a recalculated
+	 * gain value to limit how quickly the gain value will increase or decrease.
+	 * 
+	 * @param window - history size to use in detecting maximum envelope value
+	 * @param damping - a value between 0 < damping <= 1.0;
+	 */
+	public ComplexFeedForwardGainControl( int window )
+	{
+		mEnvelopeHistory = new FloatCircularBuffer( window );
+	}
+
+	@Override
+	public void receive( ComplexSample sample )
+	{
+		float envelope = sample.envelope();
+
+		if( envelope > mMaxEnvelope )
+		{
+			mMaxEnvelope = envelope;
+			
+			adjustGain();
+		}
+
+		/* Replace oldest envelope value with current envelope value */
+		float oldestEnvelope = mEnvelopeHistory.get( envelope );
+
+		/* If the oldest envelope value was the max envelope value, then we 
+		 * have to rediscover the max value from the envelope history */
+		if( mMaxEnvelope == oldestEnvelope && mMaxEnvelope != envelope )
+		{
+			mMaxEnvelope = MINIMUM_ENVELOPE;
+			
+			for( float value: mEnvelopeHistory.getBuffer() )
+			{
+				if( value > mMaxEnvelope )
+				{
+					mMaxEnvelope = value;
+				}
+			}
+			
+			adjustGain();
+		}
+		
+		/* Apply current gain value to the sample and send to the listener */
+		if( mListener != null )
+		{
+			sample.multiply( mGain );
+			
+			mListener.receive( sample );
+		}
+	}
+	
+	private void adjustGain()
+	{
+		mGain = OBJECTIVE_ENVELOPE / mMaxEnvelope;
+	}
+
+	@Override
+	public void setListener( Listener<ComplexSample> listener )
+	{
+		mListener = listener;
+	}
+
+	@Override
+	public void removeListener( Listener<ComplexSample> listener )
+	{
+		mListener = null;
+	}
+}