From e69d6d8b5f83cb1de3d9ca60312b99bb28bedb70 Mon Sep 17 00:00:00 2001
From: Zach Pomerantz <zmp@umich.edu>
Date: Thu, 9 Mar 2017 14:20:57 -0500
Subject: [PATCH 1/2] track silent listeners in audio-mixer

---
 assignment-client/src/audio/AudioMixer.cpp      | 1 +
 assignment-client/src/audio/AudioMixerSlave.cpp | 1 +
 assignment-client/src/audio/AudioMixerStats.cpp | 2 ++
 assignment-client/src/audio/AudioMixerStats.h   | 1 +
 4 files changed, 5 insertions(+)

diff --git a/assignment-client/src/audio/AudioMixer.cpp b/assignment-client/src/audio/AudioMixer.cpp
index 2583e15760..b95c429b2d 100644
--- a/assignment-client/src/audio/AudioMixer.cpp
+++ b/assignment-client/src/audio/AudioMixer.cpp
@@ -241,6 +241,7 @@ void AudioMixer::sendStatsPacket() {
 
     statsObject["avg_streams_per_frame"] = (float)_stats.sumStreams / (float)_numStatFrames;
     statsObject["avg_listeners_per_frame"] = (float)_stats.sumListeners / (float)_numStatFrames;
+    statsObject["avg_listeners_(silent)_per_frame"] = (float)_stats.sumListenersSilent / (float)_numStatFrames;
 
     statsObject["silent_packets_per_frame"] = (float)_numSilentPackets / (float)_numStatFrames;
 
diff --git a/assignment-client/src/audio/AudioMixerSlave.cpp b/assignment-client/src/audio/AudioMixerSlave.cpp
index 6b53de89c2..8edef785b8 100644
--- a/assignment-client/src/audio/AudioMixerSlave.cpp
+++ b/assignment-client/src/audio/AudioMixerSlave.cpp
@@ -106,6 +106,7 @@ void AudioMixerSlave::mix(const SharedNodePointer& node) {
 
             sendMixPacket(node, *data, encodedBuffer);
         } else {
+            ++stats.sumListenersSilent;
             sendSilentPacket(node, *data);
         }
 
diff --git a/assignment-client/src/audio/AudioMixerStats.cpp b/assignment-client/src/audio/AudioMixerStats.cpp
index a831210871..4cfdd55167 100644
--- a/assignment-client/src/audio/AudioMixerStats.cpp
+++ b/assignment-client/src/audio/AudioMixerStats.cpp
@@ -14,6 +14,7 @@
 void AudioMixerStats::reset() {
     sumStreams = 0;
     sumListeners = 0;
+    sumListenersSilent = 0;
     totalMixes = 0;
     hrtfRenders = 0;
     hrtfSilentRenders = 0;
@@ -28,6 +29,7 @@ void AudioMixerStats::reset() {
 void AudioMixerStats::accumulate(const AudioMixerStats& otherStats) {
     sumStreams += otherStats.sumStreams;
     sumListeners += otherStats.sumListeners;
+    sumListenersSilent += otherStats.sumListenersSilent;
     totalMixes += otherStats.totalMixes;
     hrtfRenders += otherStats.hrtfRenders;
     hrtfSilentRenders += otherStats.hrtfSilentRenders;
diff --git a/assignment-client/src/audio/AudioMixerStats.h b/assignment-client/src/audio/AudioMixerStats.h
index 77ac8b985d..f4ba9db769 100644
--- a/assignment-client/src/audio/AudioMixerStats.h
+++ b/assignment-client/src/audio/AudioMixerStats.h
@@ -19,6 +19,7 @@
 struct AudioMixerStats {
     int sumStreams { 0 };
     int sumListeners { 0 };
+    int sumListenersSilent { 0 };
 
     int totalMixes { 0 };
 

From 7e2f1a6455deb0263aced407154c3f88f7451316 Mon Sep 17 00:00:00 2001
From: Zach Pomerantz <zmp@umich.edu>
Date: Wed, 8 Mar 2017 02:59:48 -0500
Subject: [PATCH 2/2] check for silent samples befor limiting

---
 assignment-client/src/audio/AudioMixerSlave.cpp | 12 +++++++-----
 1 file changed, 7 insertions(+), 5 deletions(-)

diff --git a/assignment-client/src/audio/AudioMixerSlave.cpp b/assignment-client/src/audio/AudioMixerSlave.cpp
index 8edef785b8..d01d961e33 100644
--- a/assignment-client/src/audio/AudioMixerSlave.cpp
+++ b/assignment-client/src/audio/AudioMixerSlave.cpp
@@ -222,17 +222,19 @@ bool AudioMixerSlave::prepareMix(const SharedNodePointer& listener) {
     stats.mixTime += mixTime.count();
 #endif
 
-    // use the per listener AudioLimiter to render the mixed data...
-    listenerData->audioLimiter.render(_mixSamples, _bufferSamples, AudioConstants::NETWORK_FRAME_SAMPLES_PER_CHANNEL);
-
-    // check for silent audio after the peak limiter has converted the samples
+    // check for silent audio before limiting
+    // limiting uses a dither and can only guarantee abs(sample) <= 1
     bool hasAudio = false;
     for (int i = 0; i < AudioConstants::NETWORK_FRAME_SAMPLES_STEREO; ++i) {
-        if (_bufferSamples[i] != 0) {
+        if (_mixSamples[i] != 0.0f) {
             hasAudio = true;
             break;
         }
     }
+
+    // use the per listener AudioLimiter to render the mixed data
+    listenerData->audioLimiter.render(_mixSamples, _bufferSamples, AudioConstants::NETWORK_FRAME_SAMPLES_PER_CHANNEL);
+
     return hasAudio;
 }