The Tor Browser: content/media/webaudio/blink/DynamicsCompressorKernel.cpp@44a2da4a2ab2 (annotated)

content/media/webaudio/blink/DynamicsCompressorKernel.cpp@44a2da4a2ab2 (annotated)

content/media/webaudio/blink/DynamicsCompressorKernel.cpp

Fri, 16 Jan 2015 04:50:19 +0100

author: Michael Schloh von Bennewitz <michael@schloh.com>
date: Fri, 16 Jan 2015 04:50:19 +0100
branch: TOR_BUG_9701
changeset 13: 44a2da4a2ab2
permissions: -rw-r--r--

Replace accessor implementation with direct member state manipulation, by
request https://trac.torproject.org/projects/tor/ticket/9701#comment:32

 /*
  * Copyright (C) 2011 Google Inc. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions
  * are met:
  *
  * 1.  Redistributions of source code must retain the above copyright
  *     notice, this list of conditions and the following disclaimer.
  * 2.  Redistributions in binary form must reproduce the above copyright
  *     notice, this list of conditions and the following disclaimer in the
  *     documentation and/or other materials provided with the distribution.
  * 3.  Neither the name of Apple Computer, Inc. ("Apple") nor the names of
  *     its contributors may be used to endorse or promote products derived
  *     from this software without specific prior written permission.
  *
  * THIS SOFTWARE IS PROVIDED BY APPLE AND ITS CONTRIBUTORS "AS IS" AND ANY
  * EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED
  * WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
  * DISCLAIMED. IN NO EVENT SHALL APPLE OR ITS CONTRIBUTORS BE LIABLE FOR ANY
  * DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES
  * (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
  * LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND
  * ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
  * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
  * THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
  */
 #include "DynamicsCompressorKernel.h"
 #include "DenormalDisabler.h"
 #include <algorithm>
 #include "mozilla/FloatingPoint.h"
 #include "mozilla/Constants.h"
 #include "WebAudioUtils.h"
 using namespace std;
 using namespace mozilla::dom; // for WebAudioUtils
 using mozilla::IsInfinite;
 using mozilla::IsNaN;
 namespace WebCore {
 // Metering hits peaks instantly, but releases this fast (in seconds).
 const float meteringReleaseTimeConstant = 0.325f;
 const float uninitializedValue = -1;
 DynamicsCompressorKernel::DynamicsCompressorKernel(float sampleRate, unsigned numberOfChannels)
     : m_sampleRate(sampleRate)
     , m_lastPreDelayFrames(DefaultPreDelayFrames)
     , m_preDelayReadIndex(0)
     , m_preDelayWriteIndex(DefaultPreDelayFrames)
     , m_ratio(uninitializedValue)
     , m_slope(uninitializedValue)
     , m_linearThreshold(uninitializedValue)
     , m_dbThreshold(uninitializedValue)
     , m_dbKnee(uninitializedValue)
     , m_kneeThreshold(uninitializedValue)
     , m_kneeThresholdDb(uninitializedValue)
     , m_ykneeThresholdDb(uninitializedValue)
     , m_K(uninitializedValue)
 {
     setNumberOfChannels(numberOfChannels);
     // Initializes most member variables
     reset();
     m_meteringReleaseK =
         static_cast<float>(WebAudioUtils::DiscreteTimeConstantForSampleRate(meteringReleaseTimeConstant, sampleRate));
 }
 size_t DynamicsCompressorKernel::sizeOfExcludingThis(mozilla::MallocSizeOf aMallocSizeOf) const
 {
     size_t amount = 0;
     amount += m_preDelayBuffers.SizeOfExcludingThis(aMallocSizeOf);
     for (size_t i = 0; i < m_preDelayBuffers.Length(); i++) {
         amount += m_preDelayBuffers[i].SizeOfExcludingThis(aMallocSizeOf);
     }
     return amount;
 }
 void DynamicsCompressorKernel::setNumberOfChannels(unsigned numberOfChannels)
 {
     if (m_preDelayBuffers.Length() == numberOfChannels)
         return;
     m_preDelayBuffers.Clear();
     for (unsigned i = 0; i < numberOfChannels; ++i)
         m_preDelayBuffers.AppendElement(new float[MaxPreDelayFrames]);
 }
 void DynamicsCompressorKernel::setPreDelayTime(float preDelayTime)
 {
     // Re-configure look-ahead section pre-delay if delay time has changed.
     unsigned preDelayFrames = preDelayTime * sampleRate();
     if (preDelayFrames > MaxPreDelayFrames - 1)
         preDelayFrames = MaxPreDelayFrames - 1;
     if (m_lastPreDelayFrames != preDelayFrames) {
         m_lastPreDelayFrames = preDelayFrames;
         for (unsigned i = 0; i < m_preDelayBuffers.Length(); ++i)
             memset(m_preDelayBuffers[i], 0, sizeof(float) * MaxPreDelayFrames);
         m_preDelayReadIndex = 0;
         m_preDelayWriteIndex = preDelayFrames;
     }
 }
 // Exponential curve for the knee.
 // It is 1st derivative matched at m_linearThreshold and asymptotically approaches the value m_linearThreshold + 1 / k.
 float DynamicsCompressorKernel::kneeCurve(float x, float k)
 {
     // Linear up to threshold.
     if (x < m_linearThreshold)
         return x;
     return m_linearThreshold + (1 - expf(-k * (x - m_linearThreshold))) / k;
 }
 // Full compression curve with constant ratio after knee.
 float DynamicsCompressorKernel::saturate(float x, float k)
 {
     float y;
     if (x < m_kneeThreshold)
         y = kneeCurve(x, k);
     else {
         // Constant ratio after knee.
         float xDb = WebAudioUtils::ConvertLinearToDecibels(x, -1000.0f);
         float yDb = m_ykneeThresholdDb + m_slope * (xDb - m_kneeThresholdDb);
         y = WebAudioUtils::ConvertDecibelsToLinear(yDb);
     }
     return y;
 }
 // Approximate 1st derivative with input and output expressed in dB.
 // This slope is equal to the inverse of the compression "ratio".
 // In other words, a compression ratio of 20 would be a slope of 1/20.
 float DynamicsCompressorKernel::slopeAt(float x, float k)
 {
     if (x < m_linearThreshold)
         return 1;
     float x2 = x * 1.001;
     float xDb = WebAudioUtils::ConvertLinearToDecibels(x, -1000.0f);
     float x2Db = WebAudioUtils::ConvertLinearToDecibels(x2, -1000.0f);
     float yDb = WebAudioUtils::ConvertLinearToDecibels(kneeCurve(x, k), -1000.0f);
     float y2Db = WebAudioUtils::ConvertLinearToDecibels(kneeCurve(x2, k), -1000.0f);
     float m = (y2Db - yDb) / (x2Db - xDb);
     return m;
 }
 float DynamicsCompressorKernel::kAtSlope(float desiredSlope)
 {
     float xDb = m_dbThreshold + m_dbKnee;
     float x = WebAudioUtils::ConvertDecibelsToLinear(xDb);
     // Approximate k given initial values.
     float minK = 0.1;
     float maxK = 10000;
     float k = 5;
     for (int i = 0; i < 15; ++i) {
         // A high value for k will more quickly asymptotically approach a slope of 0.
         float slope = slopeAt(x, k);
         if (slope < desiredSlope) {
             // k is too high.
             maxK = k;
         } else {
             // k is too low.
             minK = k;
         }
         // Re-calculate based on geometric mean.
         k = sqrtf(minK * maxK);
     }
     return k;
 }
 float DynamicsCompressorKernel::updateStaticCurveParameters(float dbThreshold, float dbKnee, float ratio)
 {
     if (dbThreshold != m_dbThreshold || dbKnee != m_dbKnee || ratio != m_ratio) {
         // Threshold and knee.
         m_dbThreshold = dbThreshold;
         m_linearThreshold = WebAudioUtils::ConvertDecibelsToLinear(dbThreshold);
         m_dbKnee = dbKnee;
         // Compute knee parameters.
         m_ratio = ratio;
         m_slope = 1 / m_ratio;
         float k = kAtSlope(1 / m_ratio);
         m_kneeThresholdDb = dbThreshold + dbKnee;
         m_kneeThreshold = WebAudioUtils::ConvertDecibelsToLinear(m_kneeThresholdDb);
         m_ykneeThresholdDb = WebAudioUtils::ConvertLinearToDecibels(kneeCurve(m_kneeThreshold, k), -1000.0f);
         m_K = k;
     }
     return m_K;
 }
 void DynamicsCompressorKernel::process(float* sourceChannels[],
                                        float* destinationChannels[],
                                        unsigned numberOfChannels,
                                        unsigned framesToProcess,
                                        float dbThreshold,
                                        float dbKnee,
                                        float ratio,
                                        float attackTime,
                                        float releaseTime,
                                        float preDelayTime,
                                        float dbPostGain,
                                        float effectBlend, /* equal power crossfade */
                                        float releaseZone1,
                                        float releaseZone2,
                                        float releaseZone3,
                                        float releaseZone4
                                        )
 {
     MOZ_ASSERT(m_preDelayBuffers.Length() == numberOfChannels);
     float sampleRate = this->sampleRate();
     float dryMix = 1 - effectBlend;
     float wetMix = effectBlend;
     float k = updateStaticCurveParameters(dbThreshold, dbKnee, ratio);
     // Makeup gain.
     float fullRangeGain = saturate(1, k);
     float fullRangeMakeupGain = 1 / fullRangeGain;
     // Empirical/perceptual tuning.
     fullRangeMakeupGain = powf(fullRangeMakeupGain, 0.6f);
     float masterLinearGain = WebAudioUtils::ConvertDecibelsToLinear(dbPostGain) * fullRangeMakeupGain;
     // Attack parameters.
     attackTime = max(0.001f, attackTime);
     float attackFrames = attackTime * sampleRate;
     // Release parameters.
     float releaseFrames = sampleRate * releaseTime;
     // Detector release time.
     float satReleaseTime = 0.0025f;
     float satReleaseFrames = satReleaseTime * sampleRate;
     // Create a smooth function which passes through four points.
     // Polynomial of the form
     // y = a + b*x + c*x^2 + d*x^3 + e*x^4;
     float y1 = releaseFrames * releaseZone1;
     float y2 = releaseFrames * releaseZone2;
     float y3 = releaseFrames * releaseZone3;
     float y4 = releaseFrames * releaseZone4;
     // All of these coefficients were derived for 4th order polynomial curve fitting where the y values
     // match the evenly spaced x values as follows: (y1 : x == 0, y2 : x == 1, y3 : x == 2, y4 : x == 3)
     float kA = 0.9999999999999998f*y1 + 1.8432219684323923e-16f*y2 - 1.9373394351676423e-16f*y3 + 8.824516011816245e-18f*y4;
     float kB = -1.5788320352845888f*y1 + 2.3305837032074286f*y2 - 0.9141194204840429f*y3 + 0.1623677525612032f*y4;
     float kC = 0.5334142869106424f*y1 - 1.272736789213631f*y2 + 0.9258856042207512f*y3 - 0.18656310191776226f*y4;
     float kD = 0.08783463138207234f*y1 - 0.1694162967925622f*y2 + 0.08588057951595272f*y3 - 0.00429891410546283f*y4;
     float kE = -0.042416883008123074f*y1 + 0.1115693827987602f*y2 - 0.09764676325265872f*y3 + 0.028494263462021576f*y4;
     // x ranges from 0 -> 3       0    1    2   3
     //                           -15  -10  -5   0db
     // y calculates adaptive release frames depending on the amount of compression.
     setPreDelayTime(preDelayTime);
     const int nDivisionFrames = 32;
     const int nDivisions = framesToProcess / nDivisionFrames;
     unsigned frameIndex = 0;
     for (int i = 0; i < nDivisions; ++i) {
         // ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
         // Calculate desired gain
         // ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
         // Fix gremlins.
         if (IsNaN(m_detectorAverage))
             m_detectorAverage = 1;
         if (IsInfinite(m_detectorAverage))
             m_detectorAverage = 1;
         float desiredGain = m_detectorAverage;
         // Pre-warp so we get desiredGain after sin() warp below.
         float scaledDesiredGain = asinf(desiredGain) / (0.5f * M_PI);
         // ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
         // Deal with envelopes
         // ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
         // envelopeRate is the rate we slew from current compressor level to the desired level.
         // The exact rate depends on if we're attacking or releasing and by how much.
         float envelopeRate;
         bool isReleasing = scaledDesiredGain > m_compressorGain;
         // compressionDiffDb is the difference between current compression level and the desired level.
         float compressionDiffDb = WebAudioUtils::ConvertLinearToDecibels(m_compressorGain / scaledDesiredGain, -1000.0f);
         if (isReleasing) {
             // Release mode - compressionDiffDb should be negative dB
             m_maxAttackCompressionDiffDb = -1;
             // Fix gremlins.
             if (IsNaN(compressionDiffDb))
                 compressionDiffDb = -1;
             if (IsInfinite(compressionDiffDb))
                 compressionDiffDb = -1;
             // Adaptive release - higher compression (lower compressionDiffDb)  releases faster.
             // Contain within range: -12 -> 0 then scale to go from 0 -> 3
             float x = compressionDiffDb;
             x = max(-12.0f, x);
             x = min(0.0f, x);
             x = 0.25f * (x + 12);
             // Compute adaptive release curve using 4th order polynomial.
             // Normal values for the polynomial coefficients would create a monotonically increasing function.
             float x2 = x * x;
             float x3 = x2 * x;
             float x4 = x2 * x2;
             float releaseFrames = kA + kB * x + kC * x2 + kD * x3 + kE * x4;
 #define kSpacingDb 5
             float dbPerFrame = kSpacingDb / releaseFrames;
             envelopeRate = WebAudioUtils::ConvertDecibelsToLinear(dbPerFrame);
         } else {
             // Attack mode - compressionDiffDb should be positive dB
             // Fix gremlins.
             if (IsNaN(compressionDiffDb))
                 compressionDiffDb = 1;
             if (IsInfinite(compressionDiffDb))
                 compressionDiffDb = 1;
             // As long as we're still in attack mode, use a rate based off
             // the largest compressionDiffDb we've encountered so far.
             if (m_maxAttackCompressionDiffDb == -1 || m_maxAttackCompressionDiffDb < compressionDiffDb)
                 m_maxAttackCompressionDiffDb = compressionDiffDb;
             float effAttenDiffDb = max(0.5f, m_maxAttackCompressionDiffDb);
             float x = 0.25f / effAttenDiffDb;
             envelopeRate = 1 - powf(x, 1 / attackFrames);
         }
         // ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
         // Inner loop - calculate shaped power average - apply compression.
         // ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
         {
             int preDelayReadIndex = m_preDelayReadIndex;
             int preDelayWriteIndex = m_preDelayWriteIndex;
             float detectorAverage = m_detectorAverage;
             float compressorGain = m_compressorGain;
             int loopFrames = nDivisionFrames;
             while (loopFrames--) {
                 float compressorInput = 0;
                 // Predelay signal, computing compression amount from un-delayed version.
                 for (unsigned i = 0; i < numberOfChannels; ++i) {
                     float* delayBuffer = m_preDelayBuffers[i];
                     float undelayedSource = sourceChannels[i][frameIndex];
                     delayBuffer[preDelayWriteIndex] = undelayedSource;
                     float absUndelayedSource = undelayedSource > 0 ? undelayedSource : -undelayedSource;
                     if (compressorInput < absUndelayedSource)
                         compressorInput = absUndelayedSource;
                 }
                 // Calculate shaped power on undelayed input.
                 float scaledInput = compressorInput;
                 float absInput = scaledInput > 0 ? scaledInput : -scaledInput;
                 // Put through shaping curve.
                 // This is linear up to the threshold, then enters a "knee" portion followed by the "ratio" portion.
                 // The transition from the threshold to the knee is smooth (1st derivative matched).
                 // The transition from the knee to the ratio portion is smooth (1st derivative matched).
                 float shapedInput = saturate(absInput, k);
                 float attenuation = absInput <= 0.0001f ? 1 : shapedInput / absInput;
                 float attenuationDb = -WebAudioUtils::ConvertLinearToDecibels(attenuation, -1000.0f);
                 attenuationDb = max(2.0f, attenuationDb);
                 float dbPerFrame = attenuationDb / satReleaseFrames;
                 float satReleaseRate = WebAudioUtils::ConvertDecibelsToLinear(dbPerFrame) - 1;
                 bool isRelease = (attenuation > detectorAverage);
                 float rate = isRelease ? satReleaseRate : 1;
                 detectorAverage += (attenuation - detectorAverage) * rate;
                 detectorAverage = min(1.0f, detectorAverage);
                 // Fix gremlins.
                 if (IsNaN(detectorAverage))
                     detectorAverage = 1;
                 if (IsInfinite(detectorAverage))
                     detectorAverage = 1;
                 // Exponential approach to desired gain.
                 if (envelopeRate < 1) {
                     // Attack - reduce gain to desired.
                     compressorGain += (scaledDesiredGain - compressorGain) * envelopeRate;
                 } else {
                     // Release - exponentially increase gain to 1.0
                     compressorGain *= envelopeRate;
                     compressorGain = min(1.0f, compressorGain);
                 }
                 // Warp pre-compression gain to smooth out sharp exponential transition points.
                 float postWarpCompressorGain = sinf(0.5f * M_PI * compressorGain);
                 // Calculate total gain using master gain and effect blend.
                 float totalGain = dryMix + wetMix * masterLinearGain * postWarpCompressorGain;
                 // Calculate metering.
                 float dbRealGain = 20 * log10(postWarpCompressorGain);
                 if (dbRealGain < m_meteringGain)
                     m_meteringGain = dbRealGain;
                 else
                     m_meteringGain += (dbRealGain - m_meteringGain) * m_meteringReleaseK;
                 // Apply final gain.
                 for (unsigned i = 0; i < numberOfChannels; ++i) {
                     float* delayBuffer = m_preDelayBuffers[i];
                     destinationChannels[i][frameIndex] = delayBuffer[preDelayReadIndex] * totalGain;
                 }
                 frameIndex++;
                 preDelayReadIndex = (preDelayReadIndex + 1) & MaxPreDelayFramesMask;
                 preDelayWriteIndex = (preDelayWriteIndex + 1) & MaxPreDelayFramesMask;
             }
             // Locals back to member variables.
             m_preDelayReadIndex = preDelayReadIndex;
             m_preDelayWriteIndex = preDelayWriteIndex;
             m_detectorAverage = DenormalDisabler::flushDenormalFloatToZero(detectorAverage);
             m_compressorGain = DenormalDisabler::flushDenormalFloatToZero(compressorGain);
         }
     }
 }
 void DynamicsCompressorKernel::reset()
 {
     m_detectorAverage = 0;
     m_compressorGain = 1;
     m_meteringGain = 1;
     // Predelay section.
     for (unsigned i = 0; i < m_preDelayBuffers.Length(); ++i)
         memset(m_preDelayBuffers[i], 0, sizeof(float) * MaxPreDelayFrames);
     m_preDelayReadIndex = 0;
     m_preDelayWriteIndex = DefaultPreDelayFrames;
     m_maxAttackCompressionDiffDb = -1; // uninitialized state
 }
 } // namespace WebCore

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content/media/webaudio/blink/DynamicsCompressorKernel.cpp@44a2da4a2ab2 (annotated)

content/media/webaudio/blink/DynamicsCompressorKernel.cpp