Automatic Frequency Control enhancement. Provides default AFC and ability to disable in the Decoder tab of each channel. Spectral display includes visual indicators of frequency center (grey) and current AFC offset (yellow).

src/dsp/afc/AutomaticFrequencyControl.java

@@ -0,0 +1,169 @@
+package dsp.afc;
+
+import sample.Listener;
+import source.tuner.FrequencyChangeListener;
+import buffer.FloatAveragingBuffer;
+
+public class AutomaticFrequencyControl implements Listener<Float>, 
+												  FrequencyChangeListener
+{
+	private static float LARGE_ERROR = 10000.0f;
+	private static float MEDIUM_ERROR = 5000.0f;
+	private static float SMALL_ERROR = 1000.0f;
+	private static float FINE_ERROR = 500.0f;
+	private static int SAMPLE_THRESHOLD = 15000;
+	private Mode mMode = Mode.FAST;
+	
+	private FloatAveragingBuffer mBuffer = 
+			new FloatAveragingBuffer( SAMPLE_THRESHOLD );
+
+	private int mSampleCounter = 0;
+	private int mSkipCounter = 0;
+	private int mSkipThreshold = 4;
+	private int mErrorCorrection = 0;
+	private long mCurrentFrequency;
+	private int mCurrentSampleRate;
+	private FrequencyErrorListener mListener;
+	
+	public enum Mode
+	{
+		NORMAL,FAST;
+	}
+	
+	public AutomaticFrequencyControl( FrequencyErrorListener listener )
+	{
+		mListener = listener;
+	}
+	
+	public void dispose()
+	{
+		mListener = null;
+		mBuffer = null;
+	}
+	
+	public int getErrorCorrection()
+	{
+		return mErrorCorrection;
+	}
+	
+	public void reset()
+	{
+		mErrorCorrection = 0;
+		mMode = Mode.FAST;
+		dispatch();
+	}
+	
+	private void dispatch()
+	{
+		if( mListener != null )
+		{
+			mListener.setError( mErrorCorrection );
+		}
+	}
+
+	@Override
+    public void receive( Float sample )
+    {
+		if( mMode == Mode.FAST )
+		{
+			float average = mBuffer.get( sample.floatValue() );
+			
+			mSampleCounter++;
+			
+			if( mSampleCounter >= SAMPLE_THRESHOLD )
+			{
+				mSampleCounter = 0;
+				
+				update( average );
+			}
+		}
+		else
+		{
+			mSkipCounter++;
+			
+			if( mSkipCounter >= mSkipThreshold )
+			{
+				mSkipCounter = 0;
+
+				float average = mBuffer.get( sample.floatValue() );
+				
+				mSampleCounter++;
+				
+				if( mSampleCounter >= SAMPLE_THRESHOLD )
+				{
+					mSampleCounter = 0;
+					
+					update( average );
+				}
+			}
+		}
+    }
+	
+	private void update( float average )
+	{
+		int correction = 0;
+		
+		if( average > LARGE_ERROR )
+		{
+			correction = -1000;
+			mMode = Mode.FAST;
+		}
+		else if( average > MEDIUM_ERROR )
+		{
+			correction = -500;
+			mMode = Mode.FAST;
+		}
+		else if( average > SMALL_ERROR )
+		{
+			correction = -100;
+			mMode = Mode.NORMAL;
+		}
+		else if( average > FINE_ERROR )
+		{
+			correction = -50;
+			mMode = Mode.NORMAL;
+		}
+		else if( average < -LARGE_ERROR )
+		{
+			correction = 1000;
+			mMode = Mode.FAST;
+		}
+		else if( average < -MEDIUM_ERROR )
+		{
+			correction = 500;
+			mMode = Mode.FAST;
+		}
+		else if( average < -SMALL_ERROR )
+		{
+			correction = 100;
+			mMode = Mode.NORMAL;
+		}
+		else if( average < -FINE_ERROR )
+		{
+			correction = 50;
+			mMode = Mode.NORMAL;
+		}
+
+		if( correction != 0 )
+		{
+			mErrorCorrection -= correction;
+			dispatch();
+		}
+		else
+		{
+			mMode = Mode.NORMAL;
+		}
+	}
+
+	@Override
+    public void frequencyChanged( long frequency, int bandwidth )
+    {
+		if( mCurrentFrequency != frequency || mCurrentSampleRate != bandwidth )
+		{
+			mCurrentFrequency = frequency;
+			mCurrentSampleRate = bandwidth;
+			
+			reset();
+		}
+    }
+}

src/dsp/afc/FrequencyErrorListener.java

@@ -0,0 +1,10 @@
+package dsp.afc;
+
+import source.tuner.FrequencyChangeListener;
+
+public interface FrequencyErrorListener
+{
+	public void setError( int error );
+	
+	public void addListener( FrequencyChangeListener listener );
+}

src/dsp/nbfm/NBFMDemodulator.java

@@ -17,9 +17,11 @@
  ******************************************************************************/
 package dsp.nbfm;
 
+import log.Log;
 import sample.Broadcaster;
 import sample.Listener;
 import sample.complex.ComplexSample;
+import dsp.afc.AutomaticFrequencyControl;
 import dsp.filter.ComplexFIRFilter;
 import dsp.filter.FilterFactory;
 import dsp.filter.Window.WindowType;
@@ -30,7 +32,17 @@ public class NBFMDemodulator implements Listener<ComplexSample>
 	private ComplexFIRFilter mIQFilter;
 	private FMDiscriminator mDiscriminator;
 
-	public NBFMDemodulator( double[] iqFilter, double iqGain )
+	/**
+	 * Implements a quadrature narrow-band demodulator that produces float
+	 * valued demodulated, audio filtered output samples.
+	 */
+	public NBFMDemodulator()
+	{
+		this( FilterFactory.getLowPass( 48000, 4000, 73, WindowType.HAMMING ), 
+			  1.0002, true );
+	}
+
+	public NBFMDemodulator( double[] iqFilter, double iqGain, boolean afc )
 	{
 		mIQFilter = new ComplexFIRFilter( iqFilter, iqGain );
 
@@ -54,16 +66,6 @@ public class NBFMDemodulator implements Listener<ComplexSample>
 		mIQFilter.dispose();
 	}
 	
-	/**
-	 * Implements a quadrature narrow-band demodulator that produces float
-	 * valued demodulated, audio filtered output samples.
-	 */
-	public NBFMDemodulator()
-	{
-		this( FilterFactory.getLowPass( 48000, 4000, 73, WindowType.HAMMING ), 
-			  1.0002 );
-	}
-
 	/**
 	 * Receive method for complex samples that are fed into this class to be
 	 * processed