Source/WebCore/platform/audio/HRTFElevation.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.
  * 3.  Neither the name of Apple 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 "config.h"

 #if ENABLE(WEB_AUDIO)

 #include "HRTFElevation.h"

 #include "AudioBus.h"
 #include "AudioFileReader.h"
 #include "Biquad.h"
 #include "FFTFrame.h"
 #include "HRTFDatabaseLoader.h"
 #include "HRTFPanner.h"
 #include <algorithm>
 #include <math.h>
 #include <wtf/NeverDestroyed.h>

 namespace WebCore {

 // Total number of components of an HRTF database.
 constexpr size_t TotalNumberOfResponses = 240;

 // Number of frames in an individual impulse response.
 constexpr size_t ResponseFrameSize = 256;

 // Sample-rate of the spatialization impulse responses as stored in the resource file.
 // The impulse responses may be resampled to a different sample-rate (depending on the audio hardware) when they are loaded.
 constexpr float ResponseSampleRate = 44100;

 #if PLATFORM(COCOA) || USE(GSTREAMER)
 #define USE_CONCATENATED_IMPULSE_RESPONSES
 #endif

 #ifdef USE_CONCATENATED_IMPULSE_RESPONSES
 // Lazily load a concatenated HRTF database for given subject and store it in a
 // local hash table to ensure quick efficient future retrievals.
 static AudioBus* getConcatenatedImpulseResponsesForSubject(const String& subjectName)
 {
     typedef HashMap<String, AudioBus*> AudioBusMap;
     static NeverDestroyed<AudioBusMap> audioBusMap;

     AudioBus* bus;
     AudioBusMap::iterator iterator = audioBusMap.get().find(subjectName);
     if (iterator == audioBusMap.get().end()) {
         auto concatenatedImpulseResponses = AudioBus::loadPlatformResource(subjectName.utf8().data(), ResponseSampleRate);
         ASSERT(concatenatedImpulseResponses);
         if (!concatenatedImpulseResponses)
             return 0;

         bus = concatenatedImpulseResponses.leakRef();
         audioBusMap.get().set(subjectName, bus);
     } else
         bus = iterator->value;

     size_t responseLength = bus->length();
     size_t expectedLength = static_cast<size_t>(TotalNumberOfResponses * ResponseFrameSize);

     // Check number of channels and length. For now these are fixed and known.
     bool isBusGood = responseLength == expectedLength && bus->numberOfChannels() == 2;
     ASSERT(isBusGood);
     if (!isBusGood)
         return 0;

     return bus;
 }
 #endif

 // Takes advantage of the symmetry and creates a composite version of the two measured versions.  For example, we have both azimuth 30 and -30 degrees
 // where the roles of left and right ears are reversed with respect to each other.
 bool HRTFElevation::calculateSymmetricKernelsForAzimuthElevation(int azimuth, int elevation, float sampleRate, const String& subjectName,
                                                                  RefPtr<HRTFKernel>& kernelL, RefPtr<HRTFKernel>& kernelR)
 {
     RefPtr<HRTFKernel> kernelL1;
     RefPtr<HRTFKernel> kernelR1;
     bool success = calculateKernelsForAzimuthElevation(azimuth, elevation, sampleRate, subjectName, kernelL1, kernelR1);
     if (!success)
         return false;

     // And symmetric version
     int symmetricAzimuth = !azimuth ? 0 : 360 - azimuth;

     RefPtr<HRTFKernel> kernelL2;
     RefPtr<HRTFKernel> kernelR2;
     success = calculateKernelsForAzimuthElevation(symmetricAzimuth, elevation, sampleRate, subjectName, kernelL2, kernelR2);
     if (!success)
         return false;

     // Notice L/R reversal in symmetric version.
     kernelL = HRTFKernel::createInterpolatedKernel(kernelL1.get(), kernelR2.get(), 0.5f);
     kernelR = HRTFKernel::createInterpolatedKernel(kernelR1.get(), kernelL2.get(), 0.5f);

     return true;
 }

 bool HRTFElevation::calculateKernelsForAzimuthElevation(int azimuth, int elevation, float sampleRate, const String& subjectName,
                                                         RefPtr<HRTFKernel>& kernelL, RefPtr<HRTFKernel>& kernelR)
 {
     // Valid values for azimuth are 0 -> 345 in 15 degree increments.
     // Valid values for elevation are -45 -> +90 in 15 degree increments.

     bool isAzimuthGood = azimuth >= 0 && azimuth <= 345 && (azimuth / 15) * 15 == azimuth;
     ASSERT(isAzimuthGood);
     if (!isAzimuthGood)
         return false;

     bool isElevationGood = elevation >= -45 && elevation <= 90 && (elevation / 15) * 15 == elevation;
     ASSERT(isElevationGood);
     if (!isElevationGood)
         return false;

     // Construct the resource name from the subject name, azimuth, and elevation, for example:
     // "IRC_Composite_C_R0195_T015_P000"
     // Note: the passed in subjectName is not a string passed in via JavaScript or the web.
     // It's passed in as an internal ASCII identifier and is an implementation detail.
     int positiveElevation = elevation < 0 ? elevation + 360 : elevation;

 #ifdef USE_CONCATENATED_IMPULSE_RESPONSES
     AudioBus* bus(getConcatenatedImpulseResponsesForSubject(subjectName));

     if (!bus)
         return false;

     int elevationIndex = positiveElevation / AzimuthSpacing;
     if (positiveElevation > 90)
         elevationIndex -= AzimuthSpacing;

     // The concatenated impulse response is a bus containing all
     // the elevations per azimuth, for all azimuths by increasing
     // order. So for a given azimuth and elevation we need to compute
     // the index of the wanted audio frames in the concatenated table.
     unsigned index = ((azimuth / AzimuthSpacing) * HRTFDatabase::NumberOfRawElevations) + elevationIndex;
     bool isIndexGood = index < TotalNumberOfResponses;
     ASSERT(isIndexGood);
     if (!isIndexGood)
         return false;

     // Extract the individual impulse response from the concatenated
     // responses and potentially sample-rate convert it to the desired
     // (hardware) sample-rate.
     unsigned startFrame = index * ResponseFrameSize;
     unsigned stopFrame = startFrame + ResponseFrameSize;
     auto preSampleRateConvertedResponse = AudioBus::createBufferFromRange(bus, startFrame, stopFrame);
     auto response = AudioBus::createBySampleRateConverting(preSampleRateConvertedResponse.get(), false, sampleRate);
     AudioChannel* leftEarImpulseResponse = response->channel(AudioBus::ChannelLeft);
     AudioChannel* rightEarImpulseResponse = response->channel(AudioBus::ChannelRight);
 #else
     auto resourceName = makeString("IRC_", subjectName, "_C_R0195_T", pad('0', 3, azimuth), "_P", pad('0', 3, positiveElevation)).utf8();

     RefPtr<AudioBus> impulseResponse(AudioBus::loadPlatformResource(resourceName.data(), sampleRate));

     ASSERT(impulseResponse.get());
     if (!impulseResponse.get())
         return false;

     size_t responseLength = impulseResponse->length();
     size_t expectedLength = static_cast<size_t>(256 * (sampleRate / 44100.0));

     // Check number of channels and length.  For now these are fixed and known.
     bool isBusGood = responseLength == expectedLength && impulseResponse->numberOfChannels() == 2;
     ASSERT(isBusGood);
     if (!isBusGood)
         return false;

     AudioChannel* leftEarImpulseResponse = impulseResponse->channelByType(AudioBus::ChannelLeft);
     AudioChannel* rightEarImpulseResponse = impulseResponse->channelByType(AudioBus::ChannelRight);
 #endif

     // Note that depending on the fftSize returned by the panner, we may be truncating the impulse response we just loaded in.
     const size_t fftSize = HRTFPanner::fftSizeForSampleRate(sampleRate);
     kernelL = HRTFKernel::create(leftEarImpulseResponse, fftSize, sampleRate);
     kernelR = HRTFKernel::create(rightEarImpulseResponse, fftSize, sampleRate);

     return true;
 }

 // The range of elevations for the IRCAM impulse responses varies depending on azimuth, but the minimum elevation appears to always be -45.
 //
 // Here's how it goes:
 static const int maxElevations[] = {
         //  Azimuth
         //
     90, // 0
     45, // 15
     60, // 30
     45, // 45
     75, // 60
     45, // 75
     60, // 90
     45, // 105
     75, // 120
     45, // 135
     60, // 150
     45, // 165
     75, // 180
     45, // 195
     60, // 210
     45, // 225
     75, // 240
     45, // 255
     60, // 270
     45, // 285
     75, // 300
     45, // 315
     60, // 330
     45 //  345
 };

 std::unique_ptr<HRTFElevation> HRTFElevation::createForSubject(const String& subjectName, int elevation, float sampleRate)
 {
     bool isElevationGood = elevation >= -45 && elevation <= 90 && (elevation / 15) * 15 == elevation;
     ASSERT(isElevationGood);
     if (!isElevationGood)
         return nullptr;

     auto kernelListL = makeUnique<HRTFKernelList>(NumberOfTotalAzimuths);
     auto kernelListR = makeUnique<HRTFKernelList>(NumberOfTotalAzimuths);

     // Load convolution kernels from HRTF files.
     int interpolatedIndex = 0;
     for (unsigned rawIndex = 0; rawIndex < NumberOfRawAzimuths; ++rawIndex) {
         // Don't let elevation exceed maximum for this azimuth.
         int maxElevation = maxElevations[rawIndex];
         int actualElevation = std::min(elevation, maxElevation);

         bool success = calculateKernelsForAzimuthElevation(rawIndex * AzimuthSpacing, actualElevation, sampleRate, subjectName, kernelListL->at(interpolatedIndex), kernelListR->at(interpolatedIndex));
         if (!success)
             return nullptr;

         interpolatedIndex += InterpolationFactor;
     }

     // Now go back and interpolate intermediate azimuth values.
     for (unsigned i = 0; i < NumberOfTotalAzimuths; i += InterpolationFactor) {
         int j = (i + InterpolationFactor) % NumberOfTotalAzimuths;

         // Create the interpolated convolution kernels and delays.
         for (unsigned jj = 1; jj < InterpolationFactor; ++jj) {
             float x = float(jj) / float(InterpolationFactor); // interpolate from 0 -> 1

             (*kernelListL)[i + jj] = HRTFKernel::createInterpolatedKernel(kernelListL->at(i).get(), kernelListL->at(j).get(), x);
             (*kernelListR)[i + jj] = HRTFKernel::createInterpolatedKernel(kernelListR->at(i).get(), kernelListR->at(j).get(), x);
         }
     }

     return makeUnique<HRTFElevation>(WTFMove(kernelListL), WTFMove(kernelListR), elevation, sampleRate);
 }

 std::unique_ptr<HRTFElevation> HRTFElevation::createByInterpolatingSlices(HRTFElevation* hrtfElevation1, HRTFElevation* hrtfElevation2, float x, float sampleRate)
 {
     ASSERT(hrtfElevation1 && hrtfElevation2);
     if (!hrtfElevation1 || !hrtfElevation2)
         return nullptr;

     ASSERT(x >= 0.0 && x < 1.0);

     auto kernelListL = makeUnique<HRTFKernelList>(NumberOfTotalAzimuths);
     auto kernelListR = makeUnique<HRTFKernelList>(NumberOfTotalAzimuths);

     HRTFKernelList* kernelListL1 = hrtfElevation1->kernelListL();
     HRTFKernelList* kernelListR1 = hrtfElevation1->kernelListR();
     HRTFKernelList* kernelListL2 = hrtfElevation2->kernelListL();
     HRTFKernelList* kernelListR2 = hrtfElevation2->kernelListR();

     // Interpolate kernels of corresponding azimuths of the two elevations.
     for (unsigned i = 0; i < NumberOfTotalAzimuths; ++i) {
         (*kernelListL)[i] = HRTFKernel::createInterpolatedKernel(kernelListL1->at(i).get(), kernelListL2->at(i).get(), x);
         (*kernelListR)[i] = HRTFKernel::createInterpolatedKernel(kernelListR1->at(i).get(), kernelListR2->at(i).get(), x);
     }

     // Interpolate elevation angle.
     double angle = (1.0 - x) * hrtfElevation1->elevationAngle() + x * hrtfElevation2->elevationAngle();

     return makeUnique<HRTFElevation>(WTFMove(kernelListL), WTFMove(kernelListR), static_cast<int>(angle), sampleRate);
 }

 void HRTFElevation::getKernelsFromAzimuth(double azimuthBlend, unsigned azimuthIndex, HRTFKernel* &kernelL, HRTFKernel* &kernelR, double& frameDelayL, double& frameDelayR)
 {
     bool checkAzimuthBlend = azimuthBlend >= 0.0 && azimuthBlend < 1.0;
     ASSERT(checkAzimuthBlend);
     if (!checkAzimuthBlend)
         azimuthBlend = 0.0;

     unsigned numKernels = m_kernelListL->size();

     bool isIndexGood = azimuthIndex < numKernels;
     ASSERT(isIndexGood);
     if (!isIndexGood) {
         kernelL = 0;
         kernelR = 0;
         return;
     }

     // Return the left and right kernels.
     kernelL = m_kernelListL->at(azimuthIndex).get();
     kernelR = m_kernelListR->at(azimuthIndex).get();

     frameDelayL = m_kernelListL->at(azimuthIndex)->frameDelay();
     frameDelayR = m_kernelListR->at(azimuthIndex)->frameDelay();

     int azimuthIndex2 = (azimuthIndex + 1) % numKernels;
     double frameDelay2L = m_kernelListL->at(azimuthIndex2)->frameDelay();
     double frameDelay2R = m_kernelListR->at(azimuthIndex2)->frameDelay();

     // Linearly interpolate delays.
     frameDelayL = (1.0 - azimuthBlend) * frameDelayL + azimuthBlend * frameDelay2L;
     frameDelayR = (1.0 - azimuthBlend) * frameDelayR + azimuthBlend * frameDelay2R;
 }

 } // 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.
	* 3. Neither the name of Apple 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 "config.h"

	#if ENABLE(WEB_AUDIO)

	#include "HRTFElevation.h"

	#include "AudioBus.h"
	#include "AudioFileReader.h"
	#include "Biquad.h"
	#include "FFTFrame.h"
	#include "HRTFDatabaseLoader.h"
	#include "HRTFPanner.h"
	#include <algorithm>
	#include <math.h>
	#include <wtf/NeverDestroyed.h>

	namespace WebCore {

	// Total number of components of an HRTF database.
	constexpr size_t TotalNumberOfResponses = 240;

	// Number of frames in an individual impulse response.
	constexpr size_t ResponseFrameSize = 256;

	// Sample-rate of the spatialization impulse responses as stored in the resource file.
	// The impulse responses may be resampled to a different sample-rate (depending on the audio hardware) when they are loaded.
	constexpr float ResponseSampleRate = 44100;

	#if PLATFORM(COCOA) \|\| USE(GSTREAMER)
	#define USE_CONCATENATED_IMPULSE_RESPONSES
	#endif

	#ifdef USE_CONCATENATED_IMPULSE_RESPONSES
	// Lazily load a concatenated HRTF database for given subject and store it in a
	// local hash table to ensure quick efficient future retrievals.
	static AudioBus* getConcatenatedImpulseResponsesForSubject(const String& subjectName)
	{
	typedef HashMap<String, AudioBus*> AudioBusMap;
	static NeverDestroyed<AudioBusMap> audioBusMap;

	AudioBus* bus;
	AudioBusMap::iterator iterator = audioBusMap.get().find(subjectName);
	if (iterator == audioBusMap.get().end()) {
	auto concatenatedImpulseResponses = AudioBus::loadPlatformResource(subjectName.utf8().data(), ResponseSampleRate);
	ASSERT(concatenatedImpulseResponses);
	if (!concatenatedImpulseResponses)
	return 0;

	bus = concatenatedImpulseResponses.leakRef();
	audioBusMap.get().set(subjectName, bus);
	} else
	bus = iterator->value;

	size_t responseLength = bus->length();
	size_t expectedLength = static_cast<size_t>(TotalNumberOfResponses * ResponseFrameSize);

	// Check number of channels and length. For now these are fixed and known.
	bool isBusGood = responseLength == expectedLength && bus->numberOfChannels() == 2;
	ASSERT(isBusGood);
	if (!isBusGood)
	return 0;

	return bus;
	}
	#endif

	// Takes advantage of the symmetry and creates a composite version of the two measured versions. For example, we have both azimuth 30 and -30 degrees
	// where the roles of left and right ears are reversed with respect to each other.
	bool HRTFElevation::calculateSymmetricKernelsForAzimuthElevation(int azimuth, int elevation, float sampleRate, const String& subjectName,
	RefPtr<HRTFKernel>& kernelL, RefPtr<HRTFKernel>& kernelR)
	{
	RefPtr<HRTFKernel> kernelL1;
	RefPtr<HRTFKernel> kernelR1;
	bool success = calculateKernelsForAzimuthElevation(azimuth, elevation, sampleRate, subjectName, kernelL1, kernelR1);
	if (!success)
	return false;

	// And symmetric version
	int symmetricAzimuth = !azimuth ? 0 : 360 - azimuth;

	RefPtr<HRTFKernel> kernelL2;
	RefPtr<HRTFKernel> kernelR2;
	success = calculateKernelsForAzimuthElevation(symmetricAzimuth, elevation, sampleRate, subjectName, kernelL2, kernelR2);
	if (!success)
	return false;

	// Notice L/R reversal in symmetric version.
	kernelL = HRTFKernel::createInterpolatedKernel(kernelL1.get(), kernelR2.get(), 0.5f);
	kernelR = HRTFKernel::createInterpolatedKernel(kernelR1.get(), kernelL2.get(), 0.5f);

	return true;
	}

	bool HRTFElevation::calculateKernelsForAzimuthElevation(int azimuth, int elevation, float sampleRate, const String& subjectName,
	RefPtr<HRTFKernel>& kernelL, RefPtr<HRTFKernel>& kernelR)
	{
	// Valid values for azimuth are 0 -> 345 in 15 degree increments.
	// Valid values for elevation are -45 -> +90 in 15 degree increments.

	bool isAzimuthGood = azimuth >= 0 && azimuth <= 345 && (azimuth / 15) * 15 == azimuth;
	ASSERT(isAzimuthGood);
	if (!isAzimuthGood)
	return false;

	bool isElevationGood = elevation >= -45 && elevation <= 90 && (elevation / 15) * 15 == elevation;
	ASSERT(isElevationGood);
	if (!isElevationGood)
	return false;

	// Construct the resource name from the subject name, azimuth, and elevation, for example:
	// "IRC_Composite_C_R0195_T015_P000"
	// Note: the passed in subjectName is not a string passed in via JavaScript or the web.
	// It's passed in as an internal ASCII identifier and is an implementation detail.
	int positiveElevation = elevation < 0 ? elevation + 360 : elevation;

	#ifdef USE_CONCATENATED_IMPULSE_RESPONSES
	AudioBus* bus(getConcatenatedImpulseResponsesForSubject(subjectName));

	if (!bus)
	return false;

	int elevationIndex = positiveElevation / AzimuthSpacing;
	if (positiveElevation > 90)
	elevationIndex -= AzimuthSpacing;

	// The concatenated impulse response is a bus containing all
	// the elevations per azimuth, for all azimuths by increasing
	// order. So for a given azimuth and elevation we need to compute
	// the index of the wanted audio frames in the concatenated table.
	unsigned index = ((azimuth / AzimuthSpacing) * HRTFDatabase::NumberOfRawElevations) + elevationIndex;
	bool isIndexGood = index < TotalNumberOfResponses;
	ASSERT(isIndexGood);
	if (!isIndexGood)
	return false;

	// Extract the individual impulse response from the concatenated
	// responses and potentially sample-rate convert it to the desired
	// (hardware) sample-rate.
	unsigned startFrame = index * ResponseFrameSize;
	unsigned stopFrame = startFrame + ResponseFrameSize;
	auto preSampleRateConvertedResponse = AudioBus::createBufferFromRange(bus, startFrame, stopFrame);
	auto response = AudioBus::createBySampleRateConverting(preSampleRateConvertedResponse.get(), false, sampleRate);
	AudioChannel* leftEarImpulseResponse = response->channel(AudioBus::ChannelLeft);
	AudioChannel* rightEarImpulseResponse = response->channel(AudioBus::ChannelRight);
	#else
	auto resourceName = makeString("IRC_", subjectName, "_C_R0195_T", pad('0', 3, azimuth), "_P", pad('0', 3, positiveElevation)).utf8();

	RefPtr<AudioBus> impulseResponse(AudioBus::loadPlatformResource(resourceName.data(), sampleRate));

	ASSERT(impulseResponse.get());
	if (!impulseResponse.get())
	return false;

	size_t responseLength = impulseResponse->length();
	size_t expectedLength = static_cast<size_t>(256 * (sampleRate / 44100.0));

	// Check number of channels and length. For now these are fixed and known.
	bool isBusGood = responseLength == expectedLength && impulseResponse->numberOfChannels() == 2;
	ASSERT(isBusGood);
	if (!isBusGood)
	return false;

	AudioChannel* leftEarImpulseResponse = impulseResponse->channelByType(AudioBus::ChannelLeft);
	AudioChannel* rightEarImpulseResponse = impulseResponse->channelByType(AudioBus::ChannelRight);
	#endif

	// Note that depending on the fftSize returned by the panner, we may be truncating the impulse response we just loaded in.
	const size_t fftSize = HRTFPanner::fftSizeForSampleRate(sampleRate);
	kernelL = HRTFKernel::create(leftEarImpulseResponse, fftSize, sampleRate);
	kernelR = HRTFKernel::create(rightEarImpulseResponse, fftSize, sampleRate);

	return true;
	}

	// The range of elevations for the IRCAM impulse responses varies depending on azimuth, but the minimum elevation appears to always be -45.
	//
	// Here's how it goes:
	static const int maxElevations[] = {
	// Azimuth
	//
	90, // 0
	45, // 15
	60, // 30
	45, // 45
	75, // 60
	45, // 75
	60, // 90
	45, // 105
	75, // 120
	45, // 135
	60, // 150
	45, // 165
	75, // 180
	45, // 195
	60, // 210
	45, // 225
	75, // 240
	45, // 255
	60, // 270
	45, // 285
	75, // 300
	45, // 315
	60, // 330
	45 // 345
	};

	std::unique_ptr<HRTFElevation> HRTFElevation::createForSubject(const String& subjectName, int elevation, float sampleRate)
	{
	bool isElevationGood = elevation >= -45 && elevation <= 90 && (elevation / 15) * 15 == elevation;
	ASSERT(isElevationGood);
	if (!isElevationGood)
	return nullptr;

	auto kernelListL = makeUnique<HRTFKernelList>(NumberOfTotalAzimuths);
	auto kernelListR = makeUnique<HRTFKernelList>(NumberOfTotalAzimuths);

	// Load convolution kernels from HRTF files.
	int interpolatedIndex = 0;
	for (unsigned rawIndex = 0; rawIndex < NumberOfRawAzimuths; ++rawIndex) {
	// Don't let elevation exceed maximum for this azimuth.
	int maxElevation = maxElevations[rawIndex];
	int actualElevation = std::min(elevation, maxElevation);

	bool success = calculateKernelsForAzimuthElevation(rawIndex * AzimuthSpacing, actualElevation, sampleRate, subjectName, kernelListL->at(interpolatedIndex), kernelListR->at(interpolatedIndex));
	if (!success)
	return nullptr;

	interpolatedIndex += InterpolationFactor;
	}

	// Now go back and interpolate intermediate azimuth values.
	for (unsigned i = 0; i < NumberOfTotalAzimuths; i += InterpolationFactor) {
	int j = (i + InterpolationFactor) % NumberOfTotalAzimuths;

	// Create the interpolated convolution kernels and delays.
	for (unsigned jj = 1; jj < InterpolationFactor; ++jj) {
	float x = float(jj) / float(InterpolationFactor); // interpolate from 0 -> 1

	(*kernelListL)[i + jj] = HRTFKernel::createInterpolatedKernel(kernelListL->at(i).get(), kernelListL->at(j).get(), x);
	(*kernelListR)[i + jj] = HRTFKernel::createInterpolatedKernel(kernelListR->at(i).get(), kernelListR->at(j).get(), x);
	}
	}

	return makeUnique<HRTFElevation>(WTFMove(kernelListL), WTFMove(kernelListR), elevation, sampleRate);
	}

	std::unique_ptr<HRTFElevation> HRTFElevation::createByInterpolatingSlices(HRTFElevation* hrtfElevation1, HRTFElevation* hrtfElevation2, float x, float sampleRate)
	{
	ASSERT(hrtfElevation1 && hrtfElevation2);
	if (!hrtfElevation1 \|\| !hrtfElevation2)
	return nullptr;

	ASSERT(x >= 0.0 && x < 1.0);

	auto kernelListL = makeUnique<HRTFKernelList>(NumberOfTotalAzimuths);
	auto kernelListR = makeUnique<HRTFKernelList>(NumberOfTotalAzimuths);

	HRTFKernelList* kernelListL1 = hrtfElevation1->kernelListL();
	HRTFKernelList* kernelListR1 = hrtfElevation1->kernelListR();
	HRTFKernelList* kernelListL2 = hrtfElevation2->kernelListL();
	HRTFKernelList* kernelListR2 = hrtfElevation2->kernelListR();

	// Interpolate kernels of corresponding azimuths of the two elevations.
	for (unsigned i = 0; i < NumberOfTotalAzimuths; ++i) {
	(*kernelListL)[i] = HRTFKernel::createInterpolatedKernel(kernelListL1->at(i).get(), kernelListL2->at(i).get(), x);
	(*kernelListR)[i] = HRTFKernel::createInterpolatedKernel(kernelListR1->at(i).get(), kernelListR2->at(i).get(), x);
	}

	// Interpolate elevation angle.
	double angle = (1.0 - x) * hrtfElevation1->elevationAngle() + x * hrtfElevation2->elevationAngle();

	return makeUnique<HRTFElevation>(WTFMove(kernelListL), WTFMove(kernelListR), static_cast<int>(angle), sampleRate);
	}

	void HRTFElevation::getKernelsFromAzimuth(double azimuthBlend, unsigned azimuthIndex, HRTFKernel* &kernelL, HRTFKernel* &kernelR, double& frameDelayL, double& frameDelayR)
	{
	bool checkAzimuthBlend = azimuthBlend >= 0.0 && azimuthBlend < 1.0;
	ASSERT(checkAzimuthBlend);
	if (!checkAzimuthBlend)
	azimuthBlend = 0.0;

	unsigned numKernels = m_kernelListL->size();

	bool isIndexGood = azimuthIndex < numKernels;
	ASSERT(isIndexGood);
	if (!isIndexGood) {
	kernelL = 0;
	kernelR = 0;
	return;
	}

	// Return the left and right kernels.
	kernelL = m_kernelListL->at(azimuthIndex).get();
	kernelR = m_kernelListR->at(azimuthIndex).get();

	frameDelayL = m_kernelListL->at(azimuthIndex)->frameDelay();
	frameDelayR = m_kernelListR->at(azimuthIndex)->frameDelay();

	int azimuthIndex2 = (azimuthIndex + 1) % numKernels;
	double frameDelay2L = m_kernelListL->at(azimuthIndex2)->frameDelay();
	double frameDelay2R = m_kernelListR->at(azimuthIndex2)->frameDelay();

	// Linearly interpolate delays.
	frameDelayL = (1.0 - azimuthBlend) * frameDelayL + azimuthBlend * frameDelay2L;
	frameDelayR = (1.0 - azimuthBlend) * frameDelayR + azimuthBlend * frameDelay2R;
	}

	} // namespace WebCore

	#endif // ENABLE(WEB_AUDIO)