From 2674df6095382bc6894265e3810c4ceb1aad9824 Mon Sep 17 00:00:00 2001
From: Ken Cooke <ken@highfidelity.io>
Date: Thu, 14 Jul 2016 18:34:07 -0700
Subject: [PATCH] Fix the distance-attenuation model (for injectors only)

The original attenuation model seems wrong, under-attenuating at close distance but completely muting after 45m.

This uses a physics-based model of -6dB per doubling of distance in free space, for the injectors. The AudioMixer model and domain settings still need to be reworked in a future PR.
---
 libraries/audio-client/src/AudioClient.cpp | 32 +++++-----------------
 libraries/audio-client/src/AudioClient.h   |  2 +-
 2 files changed, 8 insertions(+), 26 deletions(-)

diff --git a/libraries/audio-client/src/AudioClient.cpp b/libraries/audio-client/src/AudioClient.cpp
index 50039ba668..84d0146f3b 100644
--- a/libraries/audio-client/src/AudioClient.cpp
+++ b/libraries/audio-client/src/AudioClient.cpp
@@ -885,7 +885,7 @@ void AudioClient::mixLocalAudioInjectors(int16_t* inputBuffer) {
                     // calculate distance, gain and azimuth for hrtf
                     glm::vec3 relativePosition = injector->getPosition() - _positionGetter();
                     float distance = glm::max(glm::length(relativePosition), EPSILON);
-                    float gain = gainForSource(relativePosition, injector->getVolume()); 
+                    float gain = gainForSource(distance, injector->getVolume()); 
                     float azimuth = azimuthForSource(relativePosition);         
                 
                     injector->getLocalHRTF().render(_scratchBuffer, _hrtfBuffer, 1, azimuth, distance, gain, AudioConstants::NETWORK_FRAME_SAMPLES_PER_CHANNEL);
@@ -1299,37 +1299,19 @@ float AudioClient::azimuthForSource(const glm::vec3& relativePosition) {
     }
 }
 
-float AudioClient::gainForSource(const glm::vec3& relativePosition, float volume) {
-    // TODO: put these in a place where we can share with AudioMixer!
-    const float DEFAULT_ATTENUATION_PER_DOUBLING_IN_DISTANCE = 0.18f;
+float AudioClient::gainForSource(float distance, float volume) {
+
     const float ATTENUATION_BEGINS_AT_DISTANCE = 1.0f;
 
-
-    //qDebug() << "initial gain is " << volume;
-    
     // I'm assuming that the AudioMixer's getting of the stream's attenuation
     // factor is basically same as getting volume
     float gain = volume;
-    float distanceBetween = glm::length(relativePosition);
-    if (distanceBetween < EPSILON ) {
-        distanceBetween = EPSILON;
+
+    // attenuate based on distance
+    if (distance >= ATTENUATION_BEGINS_AT_DISTANCE) {
+        gain /= distance;   // attenuation = -6dB * log2(distance)
     }
 
-    // audio mixer has notion of zones.  Unsure how to map that across here...
-
-    // attenuate based on distance now
-    if (distanceBetween >= ATTENUATION_BEGINS_AT_DISTANCE) {
-        float distanceCoefficient = 1.0f - (logf(distanceBetween/ATTENUATION_BEGINS_AT_DISTANCE) / logf(2.0f)
-                * DEFAULT_ATTENUATION_PER_DOUBLING_IN_DISTANCE);
-        if (distanceCoefficient < 0.0f) {
-            distanceCoefficient = 0.0f;
-        }
-
-        gain *= distanceCoefficient;
-    }
-    
-    //qDebug() << "calculated gain as " << gain;
-
     return gain;
 }
 
diff --git a/libraries/audio-client/src/AudioClient.h b/libraries/audio-client/src/AudioClient.h
index df7b10ab04..3e4aa931a6 100644
--- a/libraries/audio-client/src/AudioClient.h
+++ b/libraries/audio-client/src/AudioClient.h
@@ -217,7 +217,7 @@ private:
     void outputFormatChanged();
     void mixLocalAudioInjectors(int16_t* inputBuffer);
     float azimuthForSource(const glm::vec3& relativePosition);
-    float gainForSource(const glm::vec3& relativePosition, float volume);
+    float gainForSource(float distance, float volume);
 
     QByteArray firstInputFrame;
     QAudioInput* _audioInput;