third_party/blink/renderer/platform/audio/hrtf_elevation.cc - 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 "third_party/blink/renderer/platform/audio/hrtf_elevation.h"

 #include <math.h>
 #include <algorithm>
 #include <memory>
 #include <utility>

 #include "base/memory/ptr_util.h"
 #include "third_party/blink/renderer/platform/audio/audio_bus.h"
 #include "third_party/blink/renderer/platform/audio/hrtf_panner.h"
 #include "third_party/blink/renderer/platform/wtf/text/string_hash.h"
 #include "third_party/blink/renderer/platform/wtf/threading_primitives.h"

 namespace blink {

 const unsigned HRTFElevation::kAzimuthSpacing = 15;
 const unsigned HRTFElevation::kNumberOfRawAzimuths = 360 / kAzimuthSpacing;
 const unsigned HRTFElevation::kInterpolationFactor = 8;
 const unsigned HRTFElevation::kNumberOfTotalAzimuths =
     kNumberOfRawAzimuths * kInterpolationFactor;

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

 // Number of frames in an individual impulse response.
 const size_t kResponseFrameSize = 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 kResponseSampleRate = 44100;

 // 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 kElevationIndexTableSize = 10;
 const int kElevationIndexTable[kElevationIndexTableSize] = {
     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 scoped_refptr<AudioBus> GetConcatenatedImpulseResponsesForSubject(
     const String& subject_name) {
   typedef HashMap<String, scoped_refptr<AudioBus>> AudioBusMap;
   DEFINE_THREAD_SAFE_STATIC_LOCAL(AudioBusMap, audio_bus_map, ());
   DEFINE_THREAD_SAFE_STATIC_LOCAL(Mutex, mutex, ());

   MutexLocker locker(mutex);
   scoped_refptr<AudioBus> bus;
   AudioBusMap::iterator iterator = audio_bus_map.find(subject_name);
   if (iterator == audio_bus_map.end()) {
     scoped_refptr<AudioBus> concatenated_impulse_responses(
         AudioBus::GetDataResource(subject_name.Utf8().data(),
                                   kResponseSampleRate));
     DCHECK(concatenated_impulse_responses);
     if (!concatenated_impulse_responses)
       return nullptr;

     bus = concatenated_impulse_responses;
     audio_bus_map.Set(subject_name, bus);
   } else
     bus = iterator->value;

   size_t response_length = bus->length();
   size_t expected_length =
       static_cast<size_t>(kTotalNumberOfResponses * kResponseFrameSize);

   // Check number of channels and length. For now these are fixed and known.
   bool is_bus_good =
       response_length == expected_length && bus->NumberOfChannels() == 2;
   DCHECK(is_bus_good);
   if (!is_bus_good)
     return nullptr;

   return bus;
 }

 bool HRTFElevation::CalculateKernelsForAzimuthElevation(
     int azimuth,
     int elevation,
     float sample_rate,
     const String& subject_name,
     std::unique_ptr<HRTFKernel>& kernel_l,
     std::unique_ptr<HRTFKernel>& kernel_r) {
   // Valid values for azimuth are 0 -> 345 in 15 degree increments.
   // Valid values for elevation are -45 -> +90 in 15 degree increments.

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

   bool is_elevation_good =
       elevation >= -45 && elevation <= 90 && (elevation / 15) * 15 == elevation;
   DCHECK(is_elevation_good);
   if (!is_elevation_good)
     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 positive_elevation = elevation < 0 ? elevation + 360 : elevation;

   scoped_refptr<AudioBus> bus(
       GetConcatenatedImpulseResponsesForSubject(subject_name));

   if (!bus)
     return false;

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

   for (int k = 0; k < kElevationIndexTableSize; ++k) {
     if (kElevationIndexTable[k] == positive_elevation) {
       elevation_index = k;
       break;
     }
   }

   bool is_elevation_index_good =
       (elevation_index >= 0) && (elevation_index < kElevationIndexTableSize);
   DCHECK(is_elevation_index_good);
   if (!is_elevation_index_good)
     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 / kAzimuthSpacing) * HRTFDatabase::kNumberOfRawElevations) +
       elevation_index;
   bool is_index_good = index < kTotalNumberOfResponses;
   DCHECK(is_index_good);
   if (!is_index_good)
     return false;

   // Extract the individual impulse response from the concatenated
   // responses and potentially sample-rate convert it to the desired
   // (hardware) sample-rate.
   unsigned start_frame = index * kResponseFrameSize;
   unsigned stop_frame = start_frame + kResponseFrameSize;
   scoped_refptr<AudioBus> pre_sample_rate_converted_response(
       AudioBus::CreateBufferFromRange(bus.get(), start_frame, stop_frame));
   scoped_refptr<AudioBus> response(AudioBus::CreateBySampleRateConverting(
       pre_sample_rate_converted_response.get(), false, sample_rate));
   AudioChannel* left_ear_impulse_response =
       response->Channel(AudioBus::kChannelLeft);
   AudioChannel* right_ear_impulse_response =
       response->Channel(AudioBus::kChannelRight);

   // Note that depending on the fftSize returned by the panner, we may be
   // truncating the impulse response we just loaded in.
   const size_t fft_size = HRTFPanner::FftSizeForSampleRate(sample_rate);
   kernel_l = std::make_unique<HRTFKernel>(left_ear_impulse_response, fft_size,
                                           sample_rate);
   kernel_r = std::make_unique<HRTFKernel>(right_ear_impulse_response, fft_size,
                                           sample_rate);

   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 g_max_elevations[] = {
     //  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& subject_name,
     int elevation,
     float sample_rate) {
   bool is_elevation_good =
       elevation >= -45 && elevation <= 90 && (elevation / 15) * 15 == elevation;
   DCHECK(is_elevation_good);
   if (!is_elevation_good)
     return nullptr;

   std::unique_ptr<HRTFKernelList> kernel_list_l =
       std::make_unique<HRTFKernelList>(kNumberOfTotalAzimuths);
   std::unique_ptr<HRTFKernelList> kernel_list_r =
       std::make_unique<HRTFKernelList>(kNumberOfTotalAzimuths);

   // Load convolution kernels from HRTF files.
   int interpolated_index = 0;
   for (unsigned raw_index = 0; raw_index < kNumberOfRawAzimuths; ++raw_index) {
     // Don't let elevation exceed maximum for this azimuth.
     int max_elevation = g_max_elevations[raw_index];
     int actual_elevation = std::min(elevation, max_elevation);

     bool success = CalculateKernelsForAzimuthElevation(
         raw_index * kAzimuthSpacing, actual_elevation, sample_rate,
         subject_name, kernel_list_l->at(interpolated_index),
         kernel_list_r->at(interpolated_index));
     if (!success)
       return nullptr;

     interpolated_index += kInterpolationFactor;
   }

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

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

       (*kernel_list_l)[i + jj] = HRTFKernel::CreateInterpolatedKernel(
           kernel_list_l->at(i).get(), kernel_list_l->at(j).get(), x);
       (*kernel_list_r)[i + jj] = HRTFKernel::CreateInterpolatedKernel(
           kernel_list_r->at(i).get(), kernel_list_r->at(j).get(), x);
     }
   }

   std::unique_ptr<HRTFElevation> hrtf_elevation = base::WrapUnique(
       new HRTFElevation(std::move(kernel_list_l), std::move(kernel_list_r),
                         elevation, sample_rate));
   return hrtf_elevation;
 }

 std::unique_ptr<HRTFElevation> HRTFElevation::CreateByInterpolatingSlices(
     HRTFElevation* hrtf_elevation1,
     HRTFElevation* hrtf_elevation2,
     float x,
     float sample_rate) {
   DCHECK(hrtf_elevation1);
   DCHECK(hrtf_elevation2);
   if (!hrtf_elevation1 || !hrtf_elevation2)
     return nullptr;

   DCHECK_GE(x, 0.0);
   DCHECK_LT(x, 1.0);

   std::unique_ptr<HRTFKernelList> kernel_list_l =
       std::make_unique<HRTFKernelList>(kNumberOfTotalAzimuths);
   std::unique_ptr<HRTFKernelList> kernel_list_r =
       std::make_unique<HRTFKernelList>(kNumberOfTotalAzimuths);

   HRTFKernelList* kernel_list_l1 = hrtf_elevation1->KernelListL();
   HRTFKernelList* kernel_list_r1 = hrtf_elevation1->KernelListR();
   HRTFKernelList* kernel_list_l2 = hrtf_elevation2->KernelListL();
   HRTFKernelList* kernel_list_r2 = hrtf_elevation2->KernelListR();

   // Interpolate kernels of corresponding azimuths of the two elevations.
   for (unsigned i = 0; i < kNumberOfTotalAzimuths; ++i) {
     (*kernel_list_l)[i] = HRTFKernel::CreateInterpolatedKernel(
         kernel_list_l1->at(i).get(), kernel_list_l2->at(i).get(), x);
     (*kernel_list_r)[i] = HRTFKernel::CreateInterpolatedKernel(
         kernel_list_r1->at(i).get(), kernel_list_r2->at(i).get(), x);
   }

   // Interpolate elevation angle.
   double angle = (1.0 - x) * hrtf_elevation1->ElevationAngle() +
                  x * hrtf_elevation2->ElevationAngle();

   std::unique_ptr<HRTFElevation> hrtf_elevation = base::WrapUnique(
       new HRTFElevation(std::move(kernel_list_l), std::move(kernel_list_r),
                         static_cast<int>(angle), sample_rate));
   return hrtf_elevation;
 }

 void HRTFElevation::GetKernelsFromAzimuth(double azimuth_blend,
                                           unsigned azimuth_index,
                                           HRTFKernel*& kernel_l,
                                           HRTFKernel*& kernel_r,
                                           double& frame_delay_l,
                                           double& frame_delay_r) {
   bool check_azimuth_blend = azimuth_blend >= 0.0 && azimuth_blend < 1.0;
   DCHECK(check_azimuth_blend);
   if (!check_azimuth_blend)
     azimuth_blend = 0.0;

   unsigned num_kernels = kernel_list_l_->size();

   bool is_index_good = azimuth_index < num_kernels;
   DCHECK(is_index_good);
   if (!is_index_good) {
     kernel_l = nullptr;
     kernel_r = nullptr;
     return;
   }

   // Return the left and right kernels.
   kernel_l = kernel_list_l_->at(azimuth_index).get();
   kernel_r = kernel_list_r_->at(azimuth_index).get();

   frame_delay_l = kernel_list_l_->at(azimuth_index)->FrameDelay();
   frame_delay_r = kernel_list_r_->at(azimuth_index)->FrameDelay();

   int azimuth_index2 = (azimuth_index + 1) % num_kernels;
   double frame_delay2l = kernel_list_l_->at(azimuth_index2)->FrameDelay();
   double frame_delay2r = kernel_list_r_->at(azimuth_index2)->FrameDelay();

   // Linearly interpolate delays.
   frame_delay_l =
       (1.0 - azimuth_blend) * frame_delay_l + azimuth_blend * frame_delay2l;
   frame_delay_r =
       (1.0 - azimuth_blend) * frame_delay_r + azimuth_blend * frame_delay2r;
 }

 }  // 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 "third_party/blink/renderer/platform/audio/hrtf_elevation.h"

	#include <math.h>
	#include <algorithm>
	#include <memory>
	#include <utility>

	#include "base/memory/ptr_util.h"
	#include "third_party/blink/renderer/platform/audio/audio_bus.h"
	#include "third_party/blink/renderer/platform/audio/hrtf_panner.h"
	#include "third_party/blink/renderer/platform/wtf/text/string_hash.h"
	#include "third_party/blink/renderer/platform/wtf/threading_primitives.h"

	namespace blink {

	const unsigned HRTFElevation::kAzimuthSpacing = 15;
	const unsigned HRTFElevation::kNumberOfRawAzimuths = 360 / kAzimuthSpacing;
	const unsigned HRTFElevation::kInterpolationFactor = 8;
	const unsigned HRTFElevation::kNumberOfTotalAzimuths =
	kNumberOfRawAzimuths * kInterpolationFactor;

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

	// Number of frames in an individual impulse response.
	const size_t kResponseFrameSize = 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 kResponseSampleRate = 44100;

	// 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 kElevationIndexTableSize = 10;
	const int kElevationIndexTable[kElevationIndexTableSize] = {
	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 scoped_refptr<AudioBus> GetConcatenatedImpulseResponsesForSubject(
	const String& subject_name) {
	typedef HashMap<String, scoped_refptr<AudioBus>> AudioBusMap;
	DEFINE_THREAD_SAFE_STATIC_LOCAL(AudioBusMap, audio_bus_map, ());
	DEFINE_THREAD_SAFE_STATIC_LOCAL(Mutex, mutex, ());

	MutexLocker locker(mutex);
	scoped_refptr<AudioBus> bus;
	AudioBusMap::iterator iterator = audio_bus_map.find(subject_name);
	if (iterator == audio_bus_map.end()) {
	scoped_refptr<AudioBus> concatenated_impulse_responses(
	AudioBus::GetDataResource(subject_name.Utf8().data(),
	kResponseSampleRate));
	DCHECK(concatenated_impulse_responses);
	if (!concatenated_impulse_responses)
	return nullptr;

	bus = concatenated_impulse_responses;
	audio_bus_map.Set(subject_name, bus);
	} else
	bus = iterator->value;

	size_t response_length = bus->length();
	size_t expected_length =
	static_cast<size_t>(kTotalNumberOfResponses * kResponseFrameSize);

	// Check number of channels and length. For now these are fixed and known.
	bool is_bus_good =
	response_length == expected_length && bus->NumberOfChannels() == 2;
	DCHECK(is_bus_good);
	if (!is_bus_good)
	return nullptr;

	return bus;
	}

	bool HRTFElevation::CalculateKernelsForAzimuthElevation(
	int azimuth,
	int elevation,
	float sample_rate,
	const String& subject_name,
	std::unique_ptr<HRTFKernel>& kernel_l,
	std::unique_ptr<HRTFKernel>& kernel_r) {
	// Valid values for azimuth are 0 -> 345 in 15 degree increments.
	// Valid values for elevation are -45 -> +90 in 15 degree increments.

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

	bool is_elevation_good =
	elevation >= -45 && elevation <= 90 && (elevation / 15) * 15 == elevation;
	DCHECK(is_elevation_good);
	if (!is_elevation_good)
	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 positive_elevation = elevation < 0 ? elevation + 360 : elevation;

	scoped_refptr<AudioBus> bus(
	GetConcatenatedImpulseResponsesForSubject(subject_name));

	if (!bus)
	return false;

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

	for (int k = 0; k < kElevationIndexTableSize; ++k) {
	if (kElevationIndexTable[k] == positive_elevation) {
	elevation_index = k;
	break;
	}
	}

	bool is_elevation_index_good =
	(elevation_index >= 0) && (elevation_index < kElevationIndexTableSize);
	DCHECK(is_elevation_index_good);
	if (!is_elevation_index_good)
	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 / kAzimuthSpacing) * HRTFDatabase::kNumberOfRawElevations) +
	elevation_index;
	bool is_index_good = index < kTotalNumberOfResponses;
	DCHECK(is_index_good);
	if (!is_index_good)
	return false;

	// Extract the individual impulse response from the concatenated
	// responses and potentially sample-rate convert it to the desired
	// (hardware) sample-rate.
	unsigned start_frame = index * kResponseFrameSize;
	unsigned stop_frame = start_frame + kResponseFrameSize;
	scoped_refptr<AudioBus> pre_sample_rate_converted_response(
	AudioBus::CreateBufferFromRange(bus.get(), start_frame, stop_frame));
	scoped_refptr<AudioBus> response(AudioBus::CreateBySampleRateConverting(
	pre_sample_rate_converted_response.get(), false, sample_rate));
	AudioChannel* left_ear_impulse_response =
	response->Channel(AudioBus::kChannelLeft);
	AudioChannel* right_ear_impulse_response =
	response->Channel(AudioBus::kChannelRight);

	// Note that depending on the fftSize returned by the panner, we may be
	// truncating the impulse response we just loaded in.
	const size_t fft_size = HRTFPanner::FftSizeForSampleRate(sample_rate);
	kernel_l = std::make_unique<HRTFKernel>(left_ear_impulse_response, fft_size,
	sample_rate);
	kernel_r = std::make_unique<HRTFKernel>(right_ear_impulse_response, fft_size,
	sample_rate);

	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 g_max_elevations[] = {
	// 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& subject_name,
	int elevation,
	float sample_rate) {
	bool is_elevation_good =
	elevation >= -45 && elevation <= 90 && (elevation / 15) * 15 == elevation;
	DCHECK(is_elevation_good);
	if (!is_elevation_good)
	return nullptr;

	std::unique_ptr<HRTFKernelList> kernel_list_l =
	std::make_unique<HRTFKernelList>(kNumberOfTotalAzimuths);
	std::unique_ptr<HRTFKernelList> kernel_list_r =
	std::make_unique<HRTFKernelList>(kNumberOfTotalAzimuths);

	// Load convolution kernels from HRTF files.
	int interpolated_index = 0;
	for (unsigned raw_index = 0; raw_index < kNumberOfRawAzimuths; ++raw_index) {
	// Don't let elevation exceed maximum for this azimuth.
	int max_elevation = g_max_elevations[raw_index];
	int actual_elevation = std::min(elevation, max_elevation);

	bool success = CalculateKernelsForAzimuthElevation(
	raw_index * kAzimuthSpacing, actual_elevation, sample_rate,
	subject_name, kernel_list_l->at(interpolated_index),
	kernel_list_r->at(interpolated_index));
	if (!success)
	return nullptr;

	interpolated_index += kInterpolationFactor;
	}

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

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

	(*kernel_list_l)[i + jj] = HRTFKernel::CreateInterpolatedKernel(
	kernel_list_l->at(i).get(), kernel_list_l->at(j).get(), x);
	(*kernel_list_r)[i + jj] = HRTFKernel::CreateInterpolatedKernel(
	kernel_list_r->at(i).get(), kernel_list_r->at(j).get(), x);
	}
	}

	std::unique_ptr<HRTFElevation> hrtf_elevation = base::WrapUnique(
	new HRTFElevation(std::move(kernel_list_l), std::move(kernel_list_r),
	elevation, sample_rate));
	return hrtf_elevation;
	}

	std::unique_ptr<HRTFElevation> HRTFElevation::CreateByInterpolatingSlices(
	HRTFElevation* hrtf_elevation1,
	HRTFElevation* hrtf_elevation2,
	float x,
	float sample_rate) {
	DCHECK(hrtf_elevation1);
	DCHECK(hrtf_elevation2);
	if (!hrtf_elevation1 \|\| !hrtf_elevation2)
	return nullptr;

	DCHECK_GE(x, 0.0);
	DCHECK_LT(x, 1.0);

	std::unique_ptr<HRTFKernelList> kernel_list_l =
	std::make_unique<HRTFKernelList>(kNumberOfTotalAzimuths);
	std::unique_ptr<HRTFKernelList> kernel_list_r =
	std::make_unique<HRTFKernelList>(kNumberOfTotalAzimuths);

	HRTFKernelList* kernel_list_l1 = hrtf_elevation1->KernelListL();
	HRTFKernelList* kernel_list_r1 = hrtf_elevation1->KernelListR();
	HRTFKernelList* kernel_list_l2 = hrtf_elevation2->KernelListL();
	HRTFKernelList* kernel_list_r2 = hrtf_elevation2->KernelListR();

	// Interpolate kernels of corresponding azimuths of the two elevations.
	for (unsigned i = 0; i < kNumberOfTotalAzimuths; ++i) {
	(*kernel_list_l)[i] = HRTFKernel::CreateInterpolatedKernel(
	kernel_list_l1->at(i).get(), kernel_list_l2->at(i).get(), x);
	(*kernel_list_r)[i] = HRTFKernel::CreateInterpolatedKernel(
	kernel_list_r1->at(i).get(), kernel_list_r2->at(i).get(), x);
	}

	// Interpolate elevation angle.
	double angle = (1.0 - x) * hrtf_elevation1->ElevationAngle() +
	x * hrtf_elevation2->ElevationAngle();

	std::unique_ptr<HRTFElevation> hrtf_elevation = base::WrapUnique(
	new HRTFElevation(std::move(kernel_list_l), std::move(kernel_list_r),
	static_cast<int>(angle), sample_rate));
	return hrtf_elevation;
	}

	void HRTFElevation::GetKernelsFromAzimuth(double azimuth_blend,
	unsigned azimuth_index,
	HRTFKernel*& kernel_l,
	HRTFKernel*& kernel_r,
	double& frame_delay_l,
	double& frame_delay_r) {
	bool check_azimuth_blend = azimuth_blend >= 0.0 && azimuth_blend < 1.0;
	DCHECK(check_azimuth_blend);
	if (!check_azimuth_blend)
	azimuth_blend = 0.0;

	unsigned num_kernels = kernel_list_l_->size();

	bool is_index_good = azimuth_index < num_kernels;
	DCHECK(is_index_good);
	if (!is_index_good) {
	kernel_l = nullptr;
	kernel_r = nullptr;
	return;
	}

	// Return the left and right kernels.
	kernel_l = kernel_list_l_->at(azimuth_index).get();
	kernel_r = kernel_list_r_->at(azimuth_index).get();

	frame_delay_l = kernel_list_l_->at(azimuth_index)->FrameDelay();
	frame_delay_r = kernel_list_r_->at(azimuth_index)->FrameDelay();

	int azimuth_index2 = (azimuth_index + 1) % num_kernels;
	double frame_delay2l = kernel_list_l_->at(azimuth_index2)->FrameDelay();
	double frame_delay2r = kernel_list_r_->at(azimuth_index2)->FrameDelay();

	// Linearly interpolate delays.
	frame_delay_l =
	(1.0 - azimuth_blend) * frame_delay_l + azimuth_blend * frame_delay2l;
	frame_delay_r =
	(1.0 - azimuth_blend) * frame_delay_r + azimuth_blend * frame_delay2r;
	}

	} // namespace blink