#1291 Updates DC removal processing across tuner sample streams to run on a periodic timer to reduce overall processing requirements. Updates build version to 0.5.0 beta 5 (#1292)

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

src/main/java/io/github/dsheirer/buffer/SignedByteNativeBufferFactory.java

@@ -20,14 +20,51 @@
 package io.github.dsheirer.buffer;
 
 import java.nio.ByteBuffer;
+import java.util.concurrent.TimeUnit;
 
 /**
  * Implements a factory for creating SignedByteNativeBuffer instances
  */
 public class SignedByteNativeBufferFactory implements INativeBufferFactory
 {
-    private static final float DC_FILTER_GAIN = 0.02f; //Normalizes DC over period of ~50 (1 / .02) buffers
+    /**
+     * DC removal calculations will run once a minute
+     */
+    private static final long DC_PROCESSING_INTERVAL = TimeUnit.SECONDS.toMillis(60);
+
+    /**
+     * Number of buffers to process per DC calculation processing interval.
+     */
+    private static final int DC_CALCULATIONS_PER_INTERVAL = 5;
+
+    /**
+     * DC offset processing residual threshold for ending DC processing interval
+      */
+    private static final float TARGET_DC_OFFSET_REMAINING = 0.0002f;
+
+    /**
+     * Number of DC calculations remaining in the current interval
+     */
+    private int mDcCalculationsRemaining = DC_CALCULATIONS_PER_INTERVAL; //Initial value for coarse correction
+
+    /**
+     * Last time DC offset calculation interval ran
+     */
+    private long mLastDcCalculationTimestamp = 0;
+
+    /**
+     * DC offset calculation gain.
+     */
+    private static final float DC_FILTER_GAIN = 0.05f;
+
+    /**
+     * Current DC offset correction for Inphase samples
+     */
     private float mIAverageDc = 0.0f;
+
+    /**
+     * Current DC offset correction for Quadrature samples
+     */
     private float mQAverageDc = 0.0f;
 
     @Override
@@ -35,10 +72,37 @@ public class SignedByteNativeBufferFactory implements INativeBufferFactory
     {
         byte[] copy = new byte[samples.capacity()];
         samples.get(copy);
-        calculateDc(copy);
+
+        if(shouldCalculateDc())
+        {
+            calculateDc(copy);
+        }
+
         return new SignedByteNativeBuffer(copy, timestamp, mIAverageDc, mQAverageDc);
     }
 
+    /**
+     * Indicates if a DC offset calculation for a buffer should be performed.
+     */
+    private boolean shouldCalculateDc()
+    {
+        if(System.currentTimeMillis() > (mLastDcCalculationTimestamp + DC_PROCESSING_INTERVAL))
+        {
+            if(mDcCalculationsRemaining > 0)
+            {
+                return true;
+            }
+            else
+            {
+                //Reset the number of buffers to calculate and the timestamp
+                mDcCalculationsRemaining = DC_CALCULATIONS_PER_INTERVAL;
+                mLastDcCalculationTimestamp = System.currentTimeMillis();
+            }
+        }
+
+        return false;
+    }
+
     /**
      * Calculates the average DC in the sample stream so that it can be subtracted from the samples when the
      * native buffer is used.
@@ -64,5 +128,10 @@ public class SignedByteNativeBufferFactory implements INativeBufferFactory
         qDcAccumulator /= 128.0f;
         qDcAccumulator -= mQAverageDc;
         mQAverageDc += (qDcAccumulator * DC_FILTER_GAIN);
+
+        if(Math.abs(iDcAccumulator) < TARGET_DC_OFFSET_REMAINING && Math.abs(qDcAccumulator) < TARGET_DC_OFFSET_REMAINING)
+        {
+            mDcCalculationsRemaining--;
+        }
     }
 }