third_party/WebKit/Source/platform/audio/HRTFElevation.cpp - chromium/src - 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 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 "platform/audio/AudioBus.h"
 #include "platform/audio/HRTFElevation.h"
 #include "platform/audio/HRTFPanner.h"
 #include "wtf/PtrUtil.h"
 #include "wtf/ThreadingPrimitives.h"
 #include "wtf/text/StringHash.h"
 #include <algorithm>
 #include <math.h>
 #include <memory>

 namespace blink {

 const unsigned HRTFElevation::AzimuthSpacing = 15;
 const unsigned HRTFElevation::NumberOfRawAzimuths = 360 / AzimuthSpacing;
 const unsigned HRTFElevation::InterpolationFactor = 8;
 const unsigned HRTFElevation::NumberOfTotalAzimuths =
     NumberOfRawAzimuths * InterpolationFactor;

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

 // Number of frames in an individual impulse response.
 const 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.
 const float ResponseSampleRate = 44100;

 #if USE(CONCATENATED_IMPULSE_RESPONSES)

 // This table maps the index into the elevation table with the corresponding
 // angle. See https://bugs.webkit.org/show_bug.cgi?id=98294#c9 for the
 // elevation angles and their order in the concatenated response.
 const int ElevationIndexTableSize = 10;
 const int ElevationIndexTable[ElevationIndexTableSize] = {
     0, 15, 30, 45, 60, 75, 90, 315, 330, 345};

 // Lazily load a concatenated HRTF database for given subject and store it in a
 // local hash table to ensure quick efficient future retrievals.
 static PassRefPtr<AudioBus> getConcatenatedImpulseResponsesForSubject(
     const String& subjectName) {
   typedef HashMap<String, RefPtr<AudioBus>> AudioBusMap;
   DEFINE_THREAD_SAFE_STATIC_LOCAL(AudioBusMap, audioBusMap, new AudioBusMap());
   DEFINE_THREAD_SAFE_STATIC_LOCAL(Mutex, mutex, new Mutex());

   MutexLocker locker(mutex);
   RefPtr<AudioBus> bus;
   AudioBusMap::iterator iterator = audioBusMap.find(subjectName);
   if (iterator == audioBusMap.end()) {
     RefPtr<AudioBus> concatenatedImpulseResponses(
         AudioBus::loadPlatformResource(subjectName.utf8().data(),
                                        ResponseSampleRate));
     ASSERT(concatenatedImpulseResponses);
     if (!concatenatedImpulseResponses)
       return nullptr;

     bus = concatenatedImpulseResponses;
     audioBusMap.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 nullptr;

   return bus;
 }
 #endif

 bool HRTFElevation::calculateKernelsForAzimuthElevation(
     int azimuth,
     int elevation,
     float sampleRate,
     const String& subjectName,
     std::unique_ptr<HRTFKernel>& kernelL,
     std::unique_ptr<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;

 #if USE(CONCATENATED_IMPULSE_RESPONSES)
   RefPtr<AudioBus> bus(getConcatenatedImpulseResponsesForSubject(subjectName));

   if (!bus)
     return false;

   // Just sequentially search the table to find the correct index.
   int elevationIndex = -1;

   for (int k = 0; k < ElevationIndexTableSize; ++k) {
     if (ElevationIndexTable[k] == positiveElevation) {
       elevationIndex = k;
       break;
     }
   }

   bool isElevationIndexGood =
       (elevationIndex >= 0) && (elevationIndex < ElevationIndexTableSize);
   ASSERT(isElevationIndexGood);
   if (!isElevationIndexGood)
     return false;

   // 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;
   RefPtr<AudioBus> preSampleRateConvertedResponse(
       AudioBus::createBufferFromRange(bus.get(), startFrame, stopFrame));
   RefPtr<AudioBus> response(AudioBus::createBySampleRateConverting(
       preSampleRateConvertedResponse.get(), false, sampleRate));
   AudioChannel* leftEarImpulseResponse =
       response->channel(AudioBus::ChannelLeft);
   AudioChannel* rightEarImpulseResponse =
       response->channel(AudioBus::ChannelRight);
 #else
   String resourceName =
       String::format("IRC_%s_C_R0195_T%03d_P%03d", subjectName.utf8().data(),
                      azimuth, positiveElevation);

   RefPtr<AudioBus> impulseResponse(
       AudioBus::loadPlatformResource(resourceName.utf8().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 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;

   std::unique_ptr<HRTFKernelList> kernelListL =
       wrapUnique(new HRTFKernelList(NumberOfTotalAzimuths));
   std::unique_ptr<HRTFKernelList> kernelListR =
       wrapUnique(new 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);
     }
   }

   std::unique_ptr<HRTFElevation> hrtfElevation = wrapUnique(new HRTFElevation(
       std::move(kernelListL), std::move(kernelListR), elevation, sampleRate));
   return hrtfElevation;
 }

 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);

   std::unique_ptr<HRTFKernelList> kernelListL =
       wrapUnique(new HRTFKernelList(NumberOfTotalAzimuths));
   std::unique_ptr<HRTFKernelList> kernelListR =
       wrapUnique(new 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();

   std::unique_ptr<HRTFElevation> hrtfElevation = wrapUnique(
       new HRTFElevation(std::move(kernelListL), std::move(kernelListR),
                         static_cast<int>(angle), sampleRate));
   return hrtfElevation;
 }

 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 blink
	/*
	* 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 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 "platform/audio/AudioBus.h"
	#include "platform/audio/HRTFElevation.h"
	#include "platform/audio/HRTFPanner.h"
	#include "wtf/PtrUtil.h"
	#include "wtf/ThreadingPrimitives.h"
	#include "wtf/text/StringHash.h"
	#include <algorithm>
	#include <math.h>
	#include <memory>

	namespace blink {

	const unsigned HRTFElevation::AzimuthSpacing = 15;
	const unsigned HRTFElevation::NumberOfRawAzimuths = 360 / AzimuthSpacing;
	const unsigned HRTFElevation::InterpolationFactor = 8;
	const unsigned HRTFElevation::NumberOfTotalAzimuths =
	NumberOfRawAzimuths * InterpolationFactor;

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

	// Number of frames in an individual impulse response.
	const 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.
	const float ResponseSampleRate = 44100;

	#if USE(CONCATENATED_IMPULSE_RESPONSES)

	// This table maps the index into the elevation table with the corresponding
	// angle. See https://bugs.webkit.org/show_bug.cgi?id=98294#c9 for the
	// elevation angles and their order in the concatenated response.
	const int ElevationIndexTableSize = 10;
	const int ElevationIndexTable[ElevationIndexTableSize] = {
	0, 15, 30, 45, 60, 75, 90, 315, 330, 345};

	// Lazily load a concatenated HRTF database for given subject and store it in a
	// local hash table to ensure quick efficient future retrievals.
	static PassRefPtr<AudioBus> getConcatenatedImpulseResponsesForSubject(
	const String& subjectName) {
	typedef HashMap<String, RefPtr<AudioBus>> AudioBusMap;
	DEFINE_THREAD_SAFE_STATIC_LOCAL(AudioBusMap, audioBusMap, new AudioBusMap());
	DEFINE_THREAD_SAFE_STATIC_LOCAL(Mutex, mutex, new Mutex());

	MutexLocker locker(mutex);
	RefPtr<AudioBus> bus;
	AudioBusMap::iterator iterator = audioBusMap.find(subjectName);
	if (iterator == audioBusMap.end()) {
	RefPtr<AudioBus> concatenatedImpulseResponses(
	AudioBus::loadPlatformResource(subjectName.utf8().data(),
	ResponseSampleRate));
	ASSERT(concatenatedImpulseResponses);
	if (!concatenatedImpulseResponses)
	return nullptr;

	bus = concatenatedImpulseResponses;
	audioBusMap.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 nullptr;

	return bus;
	}
	#endif

	bool HRTFElevation::calculateKernelsForAzimuthElevation(
	int azimuth,
	int elevation,
	float sampleRate,
	const String& subjectName,
	std::unique_ptr<HRTFKernel>& kernelL,
	std::unique_ptr<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;

	#if USE(CONCATENATED_IMPULSE_RESPONSES)
	RefPtr<AudioBus> bus(getConcatenatedImpulseResponsesForSubject(subjectName));

	if (!bus)
	return false;

	// Just sequentially search the table to find the correct index.
	int elevationIndex = -1;

	for (int k = 0; k < ElevationIndexTableSize; ++k) {
	if (ElevationIndexTable[k] == positiveElevation) {
	elevationIndex = k;
	break;
	}
	}

	bool isElevationIndexGood =
	(elevationIndex >= 0) && (elevationIndex < ElevationIndexTableSize);
	ASSERT(isElevationIndexGood);
	if (!isElevationIndexGood)
	return false;

	// 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;
	RefPtr<AudioBus> preSampleRateConvertedResponse(
	AudioBus::createBufferFromRange(bus.get(), startFrame, stopFrame));
	RefPtr<AudioBus> response(AudioBus::createBySampleRateConverting(
	preSampleRateConvertedResponse.get(), false, sampleRate));
	AudioChannel* leftEarImpulseResponse =
	response->channel(AudioBus::ChannelLeft);
	AudioChannel* rightEarImpulseResponse =
	response->channel(AudioBus::ChannelRight);
	#else
	String resourceName =
	String::format("IRC_%s_C_R0195_T%03d_P%03d", subjectName.utf8().data(),
	azimuth, positiveElevation);

	RefPtr<AudioBus> impulseResponse(
	AudioBus::loadPlatformResource(resourceName.utf8().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 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;

	std::unique_ptr<HRTFKernelList> kernelListL =
	wrapUnique(new HRTFKernelList(NumberOfTotalAzimuths));
	std::unique_ptr<HRTFKernelList> kernelListR =
	wrapUnique(new 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);
	}
	}

	std::unique_ptr<HRTFElevation> hrtfElevation = wrapUnique(new HRTFElevation(
	std::move(kernelListL), std::move(kernelListR), elevation, sampleRate));
	return hrtfElevation;
	}

	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);

	std::unique_ptr<HRTFKernelList> kernelListL =
	wrapUnique(new HRTFKernelList(NumberOfTotalAzimuths));
	std::unique_ptr<HRTFKernelList> kernelListR =
	wrapUnique(new 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();

	std::unique_ptr<HRTFElevation> hrtfElevation = wrapUnique(
	new HRTFElevation(std::move(kernelListL), std::move(kernelListR),
	static_cast<int>(angle), sampleRate));
	return hrtfElevation;
	}

	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 blink