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/*
* 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 "HRTFKernel.h"
namespace WebCore {
// Takes the input audio channel |impulseP| as an input impulse response and
// calculates the average group delay. This represents the initial delay before
// the most energetic part of the impulse response. The sample-frame delay is
// removed from the |impulseP| impulse response, and this value is returned.
// The |length| of the passed in |impulseP| must be must be a power of 2.
static float extractAverageGroupDelay(float* impulseP, size_t length) {
// Check for power-of-2.
MOZ_ASSERT(length && (length & (length - 1)) == 0);
FFTBlock estimationFrame(length, 1.f / length);
estimationFrame.PerformFFT(impulseP);
float frameDelay =
static_cast<float>(estimationFrame.ExtractAverageGroupDelay());
estimationFrame.GetInverse(impulseP);
return frameDelay;
}
HRTFKernel::HRTFKernel(float* impulseResponse, size_t length, float sampleRate)
: m_frameDelay(0), m_sampleRate(sampleRate) {
AlignedTArray<float> buffer;
// copy to a 32-byte aligned buffer
if (((uintptr_t)impulseResponse & 31) != 0) {
buffer.SetLength(length);
mozilla::PodCopy(buffer.Elements(), impulseResponse, length);
impulseResponse = buffer.Elements();
}
// Determine the leading delay (average group delay) for the response.
m_frameDelay = extractAverageGroupDelay(impulseResponse, length);
// The FFT size (with zero padding) needs to be twice the response length
// in order to do proper convolution.
unsigned fftSize = 2 * length;
// Quick fade-out (apply window) at truncation point
// because the impulse response has been truncated.
unsigned numberOfFadeOutFrames = static_cast<unsigned>(
sampleRate / 4410); // 10 sample-frames @44.1KHz sample-rate
MOZ_ASSERT(numberOfFadeOutFrames < length);
if (numberOfFadeOutFrames < length) {
for (unsigned i = length - numberOfFadeOutFrames; i < length; ++i) {
float x =
1.0f - static_cast<float>(i - (length - numberOfFadeOutFrames)) /
numberOfFadeOutFrames;
impulseResponse[i] *= x;
}
}
m_fftFrame = mozilla::MakeUnique<FFTBlock>(fftSize);
m_fftFrame->PadAndMakeScaledDFT(impulseResponse, length);
}
// Interpolates two kernels with x: 0 -> 1 and returns the result.
nsReturnRef<HRTFKernel> HRTFKernel::createInterpolatedKernel(
HRTFKernel* kernel1, HRTFKernel* kernel2, float x) {
MOZ_ASSERT(kernel1 && kernel2);
if (!kernel1 || !kernel2) return nsReturnRef<HRTFKernel>();
MOZ_ASSERT(x >= 0.0 && x < 1.0);
x = mozilla::clamped(x, 0.0f, 1.0f);
float sampleRate1 = kernel1->sampleRate();
float sampleRate2 = kernel2->sampleRate();
MOZ_ASSERT(sampleRate1 == sampleRate2);
if (sampleRate1 != sampleRate2) return nsReturnRef<HRTFKernel>();
float frameDelay =
(1 - x) * kernel1->frameDelay() + x * kernel2->frameDelay();
UniquePtr<FFTBlock> interpolatedFrame(FFTBlock::CreateInterpolatedBlock(
*kernel1->fftFrame(), *kernel2->fftFrame(), x));
return HRTFKernel::create(std::move(interpolatedFrame), frameDelay,
sampleRate1);
}
} // namespace WebCore