Source/WebCore/Modules/webaudio/RealtimeAnalyser.cpp - WebKit - Git at Google

 /*
  * Copyright (C) 2010, 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.
  *
  * THIS SOFTWARE IS PROVIDED BY APPLE INC. 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 INC. 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 "config.h"

 #if ENABLE(WEB_AUDIO)

 #include "RealtimeAnalyser.h"

 #include "AudioBus.h"
 #include "AudioUtilities.h"
 #include "FFTFrame.h"
 #include "VectorMath.h"
 #include <JavaScriptCore/Float32Array.h>
 #include <JavaScriptCore/Uint8Array.h>
 #include <algorithm>
 #include <complex>
 #include <wtf/MainThread.h>
 #include <wtf/MathExtras.h>

 namespace WebCore {

 const double RealtimeAnalyser::DefaultSmoothingTimeConstant  = 0.8;
 const double RealtimeAnalyser::DefaultMinDecibels = -100;
 const double RealtimeAnalyser::DefaultMaxDecibels = -30;

 const unsigned RealtimeAnalyser::DefaultFFTSize = 2048;
 // All FFT implementations are expected to handle power-of-two sizes MinFFTSize <= size <= MaxFFTSize.
 const unsigned RealtimeAnalyser::MinFFTSize = 32;
 const unsigned RealtimeAnalyser::MaxFFTSize = 32768;
 const unsigned RealtimeAnalyser::InputBufferSize = RealtimeAnalyser::MaxFFTSize * 2;

 RealtimeAnalyser::RealtimeAnalyser()
     : m_inputBuffer(InputBufferSize)
     , m_writeIndex(0)
     , m_fftSize(DefaultFFTSize)
     , m_magnitudeBuffer(DefaultFFTSize / 2)
     , m_smoothingTimeConstant(DefaultSmoothingTimeConstant)
     , m_minDecibels(DefaultMinDecibels)
     , m_maxDecibels(DefaultMaxDecibels)
 {
     m_analysisFrame = makeUnique<FFTFrame>(DefaultFFTSize);
 }

 RealtimeAnalyser::~RealtimeAnalyser() = default;

 void RealtimeAnalyser::reset()
 {
     m_writeIndex = 0;
     m_inputBuffer.zero();
     m_magnitudeBuffer.zero();
 }

 bool RealtimeAnalyser::setFftSize(size_t size)
 {
     ASSERT(isMainThread());

     // Only allow powers of two.
     unsigned log2size = static_cast<unsigned>(log2(size));
     bool isPOT(1UL << log2size == size);

     if (!isPOT || size > MaxFFTSize || size < MinFFTSize)
         return false;

     if (m_fftSize != size) {
         m_analysisFrame = makeUnique<FFTFrame>(size);
         // m_magnitudeBuffer has size = fftSize / 2 because it contains floats reduced from complex values in m_analysisFrame.
         m_magnitudeBuffer.allocate(size / 2);
         m_fftSize = size;
     }

     return true;
 }

 void RealtimeAnalyser::writeInput(AudioBus* bus, size_t framesToProcess)
 {
     bool isBusGood = bus && bus->numberOfChannels() > 0 && bus->channel(0)->length() >= framesToProcess;
     ASSERT(isBusGood);
     if (!isBusGood)
         return;

     // FIXME : allow to work with non-FFTSize divisible chunking
     bool isDestinationGood = m_writeIndex < m_inputBuffer.size() && m_writeIndex + framesToProcess <= m_inputBuffer.size();
     ASSERT(isDestinationGood);
     if (!isDestinationGood)
         return;

     // Perform real-time analysis
     const float* source = bus->channel(0)->data();
     float* dest = m_inputBuffer.data() + m_writeIndex;

     // The source has already been sanity checked with isBusGood above.
     memcpy(dest, source, sizeof(float) * framesToProcess);

     // Sum all channels in one if numberOfChannels > 1.
     unsigned numberOfChannels = bus->numberOfChannels();
     if (numberOfChannels > 1) {
         for (unsigned i = 1; i < numberOfChannels; i++) {
             source = bus->channel(i)->data();
             VectorMath::vadd(dest, 1, source, 1, dest, 1, framesToProcess);
         }
         const float scale =  1.0 / numberOfChannels;
         VectorMath::vsmul(dest, 1, &scale, dest, 1, framesToProcess);
     }

     m_writeIndex += framesToProcess;
     if (m_writeIndex >= InputBufferSize)
         m_writeIndex = 0;
 }

 namespace {

 void applyWindow(float* p, size_t n)
 {
     ASSERT(isMainThread());

     // Blackman window
     double alpha = 0.16;
     double a0 = 0.5 * (1 - alpha);
     double a1 = 0.5;
     double a2 = 0.5 * alpha;

     for (unsigned i = 0; i < n; ++i) {
         double x = static_cast<double>(i) / static_cast<double>(n);
         double window = a0 - a1 * cos(2 * piDouble * x) + a2 * cos(4 * piDouble * x);
         p[i] *= float(window);
     }
 }

 } // namespace

 void RealtimeAnalyser::doFFTAnalysis()
 {
     ASSERT(isMainThread());

     // Unroll the input buffer into a temporary buffer, where we'll apply an analysis window followed by an FFT.
     size_t fftSize = this->fftSize();

     AudioFloatArray temporaryBuffer(fftSize);
     float* inputBuffer = m_inputBuffer.data();
     float* tempP = temporaryBuffer.data();

     // Take the previous fftSize values from the input buffer and copy into the temporary buffer.
     unsigned writeIndex = m_writeIndex;
     if (writeIndex < fftSize) {
         memcpy(tempP, inputBuffer + writeIndex - fftSize + InputBufferSize, sizeof(*tempP) * (fftSize - writeIndex));
         memcpy(tempP + fftSize - writeIndex, inputBuffer, sizeof(*tempP) * writeIndex);
     } else
         memcpy(tempP, inputBuffer + writeIndex - fftSize, sizeof(*tempP) * fftSize);


     // Window the input samples.
     applyWindow(tempP, fftSize);

     // Do the analysis.
     m_analysisFrame->doFFT(tempP);

     float* realP = m_analysisFrame->realData();
     float* imagP = m_analysisFrame->imagData();

     // Blow away the packed nyquist component.
     imagP[0] = 0;

     // Normalize so than an input sine wave at 0dBfs registers as 0dBfs (undo FFT scaling factor).
     const double magnitudeScale = 1.0 / fftSize;

     // A value of 0 does no averaging with the previous result.  Larger values produce slower, but smoother changes.
     double k = m_smoothingTimeConstant;
     k = std::max(0.0, k);
     k = std::min(1.0, k);

     // Convert the analysis data from complex to magnitude and average with the previous result.
     float* destination = magnitudeBuffer().data();
     size_t n = magnitudeBuffer().size();
     for (size_t i = 0; i < n; ++i) {
         std::complex<double> c(realP[i], imagP[i]);
         double scalarMagnitude = abs(c) * magnitudeScale;
         destination[i] = static_cast<float>(k * destination[i] + (1 - k) * scalarMagnitude);
     }
 }

 void RealtimeAnalyser::getFloatFrequencyData(Float32Array& destinationArray)
 {
     ASSERT(isMainThread());

     doFFTAnalysis();

     // Convert from linear magnitude to floating-point decibels.
     const double minDecibels = m_minDecibels;
     unsigned sourceLength = magnitudeBuffer().size();
     size_t length = std::min(sourceLength, destinationArray.length());
     if (length > 0) {
         const float* source = magnitudeBuffer().data();
         float* destination = destinationArray.data();

         for (size_t i = 0; i < length; ++i) {
             float linearValue = source[i];
             double dbMag = !linearValue ? minDecibels : AudioUtilities::linearToDecibels(linearValue);
             destination[i] = static_cast<float>(dbMag);
         }
     }
 }

 void RealtimeAnalyser::getByteFrequencyData(Uint8Array& destinationArray)
 {
     ASSERT(isMainThread());

     doFFTAnalysis();

     // Convert from linear magnitude to unsigned-byte decibels.
     unsigned sourceLength = magnitudeBuffer().size();
     size_t length = std::min(sourceLength, destinationArray.length());
     if (length > 0) {
         const double rangeScaleFactor = m_maxDecibels == m_minDecibels ? 1 : 1 / (m_maxDecibels - m_minDecibels);
         const double minDecibels = m_minDecibels;

         const float* source = magnitudeBuffer().data();
         unsigned char* destination = destinationArray.data();

         for (size_t i = 0; i < length; ++i) {
             float linearValue = source[i];
             double dbMag = !linearValue ? minDecibels : AudioUtilities::linearToDecibels(linearValue);

             // The range m_minDecibels to m_maxDecibels will be scaled to byte values from 0 to UCHAR_MAX.
             double scaledValue = UCHAR_MAX * (dbMag - minDecibels) * rangeScaleFactor;

             // Clip to valid range.
             if (scaledValue < 0)
                 scaledValue = 0;
             if (scaledValue > UCHAR_MAX)
                 scaledValue = UCHAR_MAX;

             destination[i] = static_cast<unsigned char>(scaledValue);
         }
     }
 }

 void RealtimeAnalyser::getFloatTimeDomainData(Float32Array& destinationArray)
 {
     ASSERT(isMainThread());

     unsigned fftSize = this->fftSize();
     size_t length = std::min(fftSize, destinationArray.length());
     if (length > 0) {
         bool isInputBufferGood = m_inputBuffer.size() == InputBufferSize && m_inputBuffer.size() > fftSize;
         ASSERT(isInputBufferGood);
         if (!isInputBufferGood)
             return;

         float* inputBuffer = m_inputBuffer.data();
         float* destination = destinationArray.data();

         unsigned writeIndex = m_writeIndex;

         for (size_t i = 0; i < length; ++i) {
             // Buffer access is protected due to modulo operation.
             destination[i] = inputBuffer[(i + writeIndex - fftSize + InputBufferSize) % InputBufferSize];
         }
     }
 }

 void RealtimeAnalyser::getByteTimeDomainData(Uint8Array& destinationArray)
 {
     ASSERT(isMainThread());

     unsigned fftSize = this->fftSize();
     size_t length = std::min(fftSize, destinationArray.length());
     if (length > 0) {
         bool isInputBufferGood = m_inputBuffer.size() == InputBufferSize && m_inputBuffer.size() > fftSize;
         ASSERT(isInputBufferGood);
         if (!isInputBufferGood)
             return;

         float* inputBuffer = m_inputBuffer.data();
         unsigned char* destination = destinationArray.data();

         unsigned writeIndex = m_writeIndex;

         for (size_t i = 0; i < length; ++i) {
             // Buffer access is protected due to modulo operation.
             float value = inputBuffer[(i + writeIndex - fftSize + InputBufferSize) % InputBufferSize];

             // Scale from nominal -1 -> +1 to unsigned byte.
             double scaledValue = 128 * (value + 1);

             // Clip to valid range.
             if (scaledValue < 0)
                 scaledValue = 0;
             if (scaledValue > UCHAR_MAX)
                 scaledValue = UCHAR_MAX;

             destination[i] = static_cast<unsigned char>(scaledValue);
         }
     }
 }

 } // namespace WebCore

 #endif // ENABLE(WEB_AUDIO)
	/*
	* Copyright (C) 2010, 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.
	*
	* THIS SOFTWARE IS PROVIDED BY APPLE INC. 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 INC. 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 "config.h"

	#if ENABLE(WEB_AUDIO)

	#include "RealtimeAnalyser.h"

	#include "AudioBus.h"
	#include "AudioUtilities.h"
	#include "FFTFrame.h"
	#include "VectorMath.h"
	#include <JavaScriptCore/Float32Array.h>
	#include <JavaScriptCore/Uint8Array.h>
	#include <algorithm>
	#include <complex>
	#include <wtf/MainThread.h>
	#include <wtf/MathExtras.h>

	namespace WebCore {

	const double RealtimeAnalyser::DefaultSmoothingTimeConstant = 0.8;
	const double RealtimeAnalyser::DefaultMinDecibels = -100;
	const double RealtimeAnalyser::DefaultMaxDecibels = -30;

	const unsigned RealtimeAnalyser::DefaultFFTSize = 2048;
	// All FFT implementations are expected to handle power-of-two sizes MinFFTSize <= size <= MaxFFTSize.
	const unsigned RealtimeAnalyser::MinFFTSize = 32;
	const unsigned RealtimeAnalyser::MaxFFTSize = 32768;
	const unsigned RealtimeAnalyser::InputBufferSize = RealtimeAnalyser::MaxFFTSize * 2;

	RealtimeAnalyser::RealtimeAnalyser()
	: m_inputBuffer(InputBufferSize)
	, m_writeIndex(0)
	, m_fftSize(DefaultFFTSize)
	, m_magnitudeBuffer(DefaultFFTSize / 2)
	, m_smoothingTimeConstant(DefaultSmoothingTimeConstant)
	, m_minDecibels(DefaultMinDecibels)
	, m_maxDecibels(DefaultMaxDecibels)
	{
	m_analysisFrame = makeUnique<FFTFrame>(DefaultFFTSize);
	}

	RealtimeAnalyser::~RealtimeAnalyser() = default;

	void RealtimeAnalyser::reset()
	{
	m_writeIndex = 0;
	m_inputBuffer.zero();
	m_magnitudeBuffer.zero();
	}

	bool RealtimeAnalyser::setFftSize(size_t size)
	{
	ASSERT(isMainThread());

	// Only allow powers of two.
	unsigned log2size = static_cast<unsigned>(log2(size));
	bool isPOT(1UL << log2size == size);

	if (!isPOT \|\| size > MaxFFTSize \|\| size < MinFFTSize)
	return false;

	if (m_fftSize != size) {
	m_analysisFrame = makeUnique<FFTFrame>(size);
	// m_magnitudeBuffer has size = fftSize / 2 because it contains floats reduced from complex values in m_analysisFrame.
	m_magnitudeBuffer.allocate(size / 2);
	m_fftSize = size;
	}

	return true;
	}

	void RealtimeAnalyser::writeInput(AudioBus* bus, size_t framesToProcess)
	{
	bool isBusGood = bus && bus->numberOfChannels() > 0 && bus->channel(0)->length() >= framesToProcess;
	ASSERT(isBusGood);
	if (!isBusGood)
	return;

	// FIXME : allow to work with non-FFTSize divisible chunking
	bool isDestinationGood = m_writeIndex < m_inputBuffer.size() && m_writeIndex + framesToProcess <= m_inputBuffer.size();
	ASSERT(isDestinationGood);
	if (!isDestinationGood)
	return;

	// Perform real-time analysis
	const float* source = bus->channel(0)->data();
	float* dest = m_inputBuffer.data() + m_writeIndex;

	// The source has already been sanity checked with isBusGood above.
	memcpy(dest, source, sizeof(float) * framesToProcess);

	// Sum all channels in one if numberOfChannels > 1.
	unsigned numberOfChannels = bus->numberOfChannels();
	if (numberOfChannels > 1) {
	for (unsigned i = 1; i < numberOfChannels; i++) {
	source = bus->channel(i)->data();
	VectorMath::vadd(dest, 1, source, 1, dest, 1, framesToProcess);
	}
	const float scale = 1.0 / numberOfChannels;
	VectorMath::vsmul(dest, 1, &scale, dest, 1, framesToProcess);
	}

	m_writeIndex += framesToProcess;
	if (m_writeIndex >= InputBufferSize)
	m_writeIndex = 0;
	}

	namespace {

	void applyWindow(float* p, size_t n)
	{
	ASSERT(isMainThread());

	// Blackman window
	double alpha = 0.16;
	double a0 = 0.5 * (1 - alpha);
	double a1 = 0.5;
	double a2 = 0.5 * alpha;

	for (unsigned i = 0; i < n; ++i) {
	double x = static_cast<double>(i) / static_cast<double>(n);
	double window = a0 - a1 * cos(2 * piDouble * x) + a2 * cos(4 * piDouble * x);
	p[i] *= float(window);
	}
	}

	} // namespace

	void RealtimeAnalyser::doFFTAnalysis()
	{
	ASSERT(isMainThread());

	// Unroll the input buffer into a temporary buffer, where we'll apply an analysis window followed by an FFT.
	size_t fftSize = this->fftSize();

	AudioFloatArray temporaryBuffer(fftSize);
	float* inputBuffer = m_inputBuffer.data();
	float* tempP = temporaryBuffer.data();

	// Take the previous fftSize values from the input buffer and copy into the temporary buffer.
	unsigned writeIndex = m_writeIndex;
	if (writeIndex < fftSize) {
	memcpy(tempP, inputBuffer + writeIndex - fftSize + InputBufferSize, sizeof(tempP) (fftSize - writeIndex));
	memcpy(tempP + fftSize - writeIndex, inputBuffer, sizeof(tempP) writeIndex);
	} else
	memcpy(tempP, inputBuffer + writeIndex - fftSize, sizeof(tempP) fftSize);


	// Window the input samples.
	applyWindow(tempP, fftSize);

	// Do the analysis.
	m_analysisFrame->doFFT(tempP);

	float* realP = m_analysisFrame->realData();
	float* imagP = m_analysisFrame->imagData();

	// Blow away the packed nyquist component.
	imagP[0] = 0;

	// Normalize so than an input sine wave at 0dBfs registers as 0dBfs (undo FFT scaling factor).
	const double magnitudeScale = 1.0 / fftSize;

	// A value of 0 does no averaging with the previous result. Larger values produce slower, but smoother changes.
	double k = m_smoothingTimeConstant;
	k = std::max(0.0, k);
	k = std::min(1.0, k);

	// Convert the analysis data from complex to magnitude and average with the previous result.
	float* destination = magnitudeBuffer().data();
	size_t n = magnitudeBuffer().size();
	for (size_t i = 0; i < n; ++i) {
	std::complex<double> c(realP[i], imagP[i]);
	double scalarMagnitude = abs(c) * magnitudeScale;
	destination[i] = static_cast<float>(k * destination[i] + (1 - k) * scalarMagnitude);
	}
	}

	void RealtimeAnalyser::getFloatFrequencyData(Float32Array& destinationArray)
	{
	ASSERT(isMainThread());

	doFFTAnalysis();

	// Convert from linear magnitude to floating-point decibels.
	const double minDecibels = m_minDecibels;
	unsigned sourceLength = magnitudeBuffer().size();
	size_t length = std::min(sourceLength, destinationArray.length());
	if (length > 0) {
	const float* source = magnitudeBuffer().data();
	float* destination = destinationArray.data();

	for (size_t i = 0; i < length; ++i) {
	float linearValue = source[i];
	double dbMag = !linearValue ? minDecibels : AudioUtilities::linearToDecibels(linearValue);
	destination[i] = static_cast<float>(dbMag);
	}
	}
	}

	void RealtimeAnalyser::getByteFrequencyData(Uint8Array& destinationArray)
	{
	ASSERT(isMainThread());

	doFFTAnalysis();

	// Convert from linear magnitude to unsigned-byte decibels.
	unsigned sourceLength = magnitudeBuffer().size();
	size_t length = std::min(sourceLength, destinationArray.length());
	if (length > 0) {
	const double rangeScaleFactor = m_maxDecibels == m_minDecibels ? 1 : 1 / (m_maxDecibels - m_minDecibels);
	const double minDecibels = m_minDecibels;

	const float* source = magnitudeBuffer().data();
	unsigned char* destination = destinationArray.data();

	for (size_t i = 0; i < length; ++i) {
	float linearValue = source[i];
	double dbMag = !linearValue ? minDecibels : AudioUtilities::linearToDecibels(linearValue);

	// The range m_minDecibels to m_maxDecibels will be scaled to byte values from 0 to UCHAR_MAX.
	double scaledValue = UCHAR_MAX * (dbMag - minDecibels) * rangeScaleFactor;

	// Clip to valid range.
	if (scaledValue < 0)
	scaledValue = 0;
	if (scaledValue > UCHAR_MAX)
	scaledValue = UCHAR_MAX;

	destination[i] = static_cast<unsigned char>(scaledValue);
	}
	}
	}

	void RealtimeAnalyser::getFloatTimeDomainData(Float32Array& destinationArray)
	{
	ASSERT(isMainThread());

	unsigned fftSize = this->fftSize();
	size_t length = std::min(fftSize, destinationArray.length());
	if (length > 0) {
	bool isInputBufferGood = m_inputBuffer.size() == InputBufferSize && m_inputBuffer.size() > fftSize;
	ASSERT(isInputBufferGood);
	if (!isInputBufferGood)
	return;

	float* inputBuffer = m_inputBuffer.data();
	float* destination = destinationArray.data();

	unsigned writeIndex = m_writeIndex;

	for (size_t i = 0; i < length; ++i) {
	// Buffer access is protected due to modulo operation.
	destination[i] = inputBuffer[(i + writeIndex - fftSize + InputBufferSize) % InputBufferSize];
	}
	}
	}

	void RealtimeAnalyser::getByteTimeDomainData(Uint8Array& destinationArray)
	{
	ASSERT(isMainThread());

	unsigned fftSize = this->fftSize();
	size_t length = std::min(fftSize, destinationArray.length());
	if (length > 0) {
	bool isInputBufferGood = m_inputBuffer.size() == InputBufferSize && m_inputBuffer.size() > fftSize;
	ASSERT(isInputBufferGood);
	if (!isInputBufferGood)
	return;

	float* inputBuffer = m_inputBuffer.data();
	unsigned char* destination = destinationArray.data();

	unsigned writeIndex = m_writeIndex;

	for (size_t i = 0; i < length; ++i) {
	// Buffer access is protected due to modulo operation.
	float value = inputBuffer[(i + writeIndex - fftSize + InputBufferSize) % InputBufferSize];

	// Scale from nominal -1 -> +1 to unsigned byte.
	double scaledValue = 128 * (value + 1);

	// Clip to valid range.
	if (scaledValue < 0)
	scaledValue = 0;
	if (scaledValue > UCHAR_MAX)
	scaledValue = UCHAR_MAX;

	destination[i] = static_cast<unsigned char>(scaledValue);
	}
	}
	}

	} // namespace WebCore

	#endif // ENABLE(WEB_AUDIO)