From 8148ca48af86ec89894edf631ac25fce07e1a917 Mon Sep 17 00:00:00 2001
From: Doug Hoffman <doug+github@hoff.mn>
Date: Sun, 1 May 2022 05:57:32 -0400
Subject: [PATCH] Normalize audio before recording (#1213)

#1213 Normalize audio before recording
---
 .../io/github/dsheirer/audio/AudioUtils.java  | 42 +++++++++++++++++++
 .../audio/convert/MP3AudioConverter.java      |  2 +
 2 files changed, 44 insertions(+)

diff --git a/src/main/java/io/github/dsheirer/audio/AudioUtils.java b/src/main/java/io/github/dsheirer/audio/AudioUtils.java
index 0f0dd223..06632176 100644
--- a/src/main/java/io/github/dsheirer/audio/AudioUtils.java
+++ b/src/main/java/io/github/dsheirer/audio/AudioUtils.java
@@ -24,7 +24,10 @@ import org.slf4j.LoggerFactory;
 
 import java.io.ByteArrayOutputStream;
 import java.io.IOException;
+import java.lang.Float;
+import java.lang.Math;
 import java.nio.ByteBuffer;
+import java.util.ArrayList;
 import java.util.List;
 
 public class AudioUtils
@@ -78,4 +81,43 @@ public class AudioUtils
 
         return stream.toByteArray();
     }
+
+    /**
+     * Normalize audio samples
+     */
+    public static List<float[]> normalize(List<float[]> audioBuffers)
+    {
+        float targetMax = 0.95f; // -0.44dBFS
+        float max = 0.1f; // Initialize at 0.1 (-20dBFS) to limit maximum gain
+
+        for(float[] audioBuffer: audioBuffers)
+        {
+            for(float value: audioBuffer)
+            {
+                float newMax = Math.max(max, Math.abs(value));
+                if(!Float.isNaN(newMax))
+                {
+                    max = newMax;
+                }
+            }
+        }
+
+        if(targetMax == max)
+        {
+            return audioBuffers;
+        }
+
+        float gain = targetMax / max;
+
+        for(float[] audioBuffer: audioBuffers)
+        {
+            for(int i=0;i<audioBuffer.length;i++)
+            {
+                audioBuffer[i] *= gain;
+            }
+        }
+
+        return audioBuffers;
+    }
+
 }
diff --git a/src/main/java/io/github/dsheirer/audio/convert/MP3AudioConverter.java b/src/main/java/io/github/dsheirer/audio/convert/MP3AudioConverter.java
index 75a5416b..2420c5f4 100644
--- a/src/main/java/io/github/dsheirer/audio/convert/MP3AudioConverter.java
+++ b/src/main/java/io/github/dsheirer/audio/convert/MP3AudioConverter.java
@@ -18,6 +18,7 @@
  */
 package io.github.dsheirer.audio.convert;
 
+import io.github.dsheirer.audio.AudioUtils;
 import io.github.dsheirer.dsp.filter.resample.RealResampler;
 import io.github.dsheirer.sample.ConversionUtils;
 import net.sourceforge.lame.lowlevel.LameEncoder;
@@ -73,6 +74,7 @@ public class MP3AudioConverter implements IAudioConverter
     public List<byte[]> convert(List<float[]> audioPackets)
     {
         List<byte[]> converted = new ArrayList<>();
+        audioPackets = AudioUtils.normalize(audioPackets);
 
         if(mResampler != null)
         {