From 08819597500b1f807f5005844e321364abcbccdd Mon Sep 17 00:00:00 2001
From: Craig Hansen-Sturm <chansensturm@comcast.net>
Date: Wed, 27 Aug 2014 17:30:11 -0700
Subject: [PATCH] left/right channels of head shadow filter now have
 independent gain + implemented all-pass filter

---
 assignment-client/src/audio/AudioMixer.cpp | 39 +++++++++++-----------
 libraries/audio/src/AudioFilter.h          | 37 ++++++++++++++++++++
 2 files changed, 56 insertions(+), 20 deletions(-)

diff --git a/assignment-client/src/audio/AudioMixer.cpp b/assignment-client/src/audio/AudioMixer.cpp
index 52a922b4e3..b0d9cae8d9 100644
--- a/assignment-client/src/audio/AudioMixer.cpp
+++ b/assignment-client/src/audio/AudioMixer.cpp
@@ -308,38 +308,37 @@ int AudioMixer::addStreamToMixForListeningNodeWithStream(PositionalAudioStream*
     if (_enableFilter && shouldAttenuate) {
         
         glm::vec3 relativePosition = streamToAdd->getPosition() - listeningNodeStream->getPosition();
-        if (relativePosition.z < 0) {  // if the source is behind us
-            
+        if (relativePosition.z < 0) {  // if the source is behind us      
             AudioFilterHSF1s& penumbraFilter = streamToAdd->getFilter();
 
             // calculate penumbra angle
             float headPenumbraAngle = glm::angle(glm::vec3(0.0f, 0.0f, -1.0f),
                                                  glm::normalize(relativePosition));
             
-            // normalize penumbra angle
-            float normalizedHeadPenumbraAngle = headPenumbraAngle / PI_OVER_TWO;
-            
-            if (normalizedHeadPenumbraAngle < EPSILON) { 
-                normalizedHeadPenumbraAngle = EPSILON;
+            if (relativePosition.x < 0) {
+                headPenumbraAngle *= -1.0f;  // [-pi/2,+pi/2]
             }
             
-            const float SQUARE_ROOT_OF_TWO_OVER_TWO = 0.71f;
+            const float SQUARE_ROOT_OF_TWO_OVER_TWO = 0.71f;  // half power
+            const float ONE_OVER_TWO_PI = 1.0f / TWO_PI;
             const float FILTER_CUTOFF_FREQUENCY_HZ = 4000.0f;
-            float penumbraFilterGain;
-            float penumbraFilterFrequency;
-            float penumbraFilterSlope;
-
-            // calculate the updated gain.  this will be tuned over time.
-            // consider this only a crude-first pass at correlating gain, freq and slope with penumbra angle.
-            penumbraFilterGain = SQUARE_ROOT_OF_TWO_OVER_TWO * (normalizedHeadPenumbraAngle + SQUARE_ROOT_OF_TWO_OVER_TWO);
-            penumbraFilterFrequency = FILTER_CUTOFF_FREQUENCY_HZ; // constant frequency
-            penumbraFilterSlope = SQUARE_ROOT_OF_TWO_OVER_TWO; // constant slope
             
-            qDebug() << "penumbra gain=" << penumbraFilterGain << ", penumbraAngle=" << normalizedHeadPenumbraAngle;
+            // calculate the updated gain, frequency and slope.  this will be tuned over time.
+            const float penumbraFilterGainL = (-1.0f * ONE_OVER_TWO_PI * headPenumbraAngle ) + SQUARE_ROOT_OF_TWO_OVER_TWO;
+            const float penumbraFilterGainR = (+1.0f * ONE_OVER_TWO_PI * headPenumbraAngle ) + SQUARE_ROOT_OF_TWO_OVER_TWO;
+            const float penumbraFilterFrequency = FILTER_CUTOFF_FREQUENCY_HZ; // constant frequency
+            const float penumbraFilterSlope = SQUARE_ROOT_OF_TWO_OVER_TWO; // constant slope
+            
+            qDebug() << "penumbra gainL=" 
+                        << penumbraFilterGainL
+                        << "penumbra gainR="
+                        << penumbraFilterGainR
+                        << "penumbraAngle="
+                        << headPenumbraAngle;
 
             // set the gain on both filter channels
-            penumbraFilter.setParameters(0, 0, SAMPLE_RATE, penumbraFilterFrequency, penumbraFilterGain, penumbraFilterSlope);
-            penumbraFilter.setParameters(0, 1, SAMPLE_RATE, penumbraFilterFrequency, penumbraFilterGain, penumbraFilterSlope);
+            penumbraFilter.setParameters(0, 0, SAMPLE_RATE, penumbraFilterFrequency, penumbraFilterGainL, penumbraFilterSlope);
+            penumbraFilter.setParameters(0, 1, SAMPLE_RATE, penumbraFilterFrequency, penumbraFilterGainR, penumbraFilterSlope);
             
             penumbraFilter.render(_clientSamples, _clientSamples, NETWORK_BUFFER_LENGTH_SAMPLES_STEREO / 2);
         }
diff --git a/libraries/audio/src/AudioFilter.h b/libraries/audio/src/AudioFilter.h
index 7c3c98582b..eb65593e51 100644
--- a/libraries/audio/src/AudioFilter.h
+++ b/libraries/audio/src/AudioFilter.h
@@ -236,6 +236,43 @@ public:
     }
 };
 
+//
+// Implements a all-pass filter using a biquad
+//
+class AudioFilterALL : 
+public AudioFilter< AudioFilterALL >
+{
+public:
+    
+    //
+    // helpers
+    //
+    void updateKernel() {
+        
+        const float omega = TWO_PI * _frequency / _sampleRate;
+        const float cosOmega = cosf(omega);
+        const float alpha = 0.5f * sinf(omega) / _slope;
+        /*
+         b0 =   1 - alpha
+         b1 =  -2*cos(w0)
+         b2 =   1 + alpha
+         a0 =   1 + alpha
+         a1 =  -2*cos(w0)
+         a2 =   1 - alpha
+         */
+        const float b0 = +1.0f - alpha;
+        const float b1 = -2.0f * cosOmega;
+        const float b2 = +1.0f + alpha;
+        const float a0 = +1.0f + alpha;
+        const float a1 = -2.0f * cosOmega;
+        const float a2 = +1.0f - alpha;
+        
+        const float normA0 = 1.0f / a0;
+        
+        _kernel.setParameters(b0 * normA0, b1 * normA0 , b2 * normA0, a1 * normA0, a2 * normA0);
+    }
+};
+
 //
 // Implements a single-band parametric EQ using a biquad "peaking EQ" configuration
 //