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100 lines
4.3 KiB
C++
100 lines
4.3 KiB
C++
/*
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* Copyright (C) 2010 Google Inc. All rights reserved.
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*
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* Redistribution and use in source and binary forms, with or without
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* modification, are permitted provided that the following conditions
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* are met:
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*
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* 1. Redistributions of source code must retain the above copyright
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* notice, this list of conditions and the following disclaimer.
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* 2. Redistributions in binary form must reproduce the above copyright
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* notice, this list of conditions and the following disclaimer in the
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* documentation and/or other materials provided with the distribution.
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* 3. Neither the name of Apple Computer, Inc. ("Apple") nor the names of
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* its contributors may be used to endorse or promote products derived
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* from this software without specific prior written permission.
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*
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* THIS SOFTWARE IS PROVIDED BY APPLE AND ITS CONTRIBUTORS "AS IS" AND ANY
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* EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED
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* WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
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* DISCLAIMED. IN NO EVENT SHALL APPLE OR ITS CONTRIBUTORS BE LIABLE FOR ANY
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* DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES
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* (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
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* LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND
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* ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
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* (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
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* THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
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*/
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#include "HRTFKernel.h"
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namespace WebCore {
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// Takes the input audio channel |impulseP| as an input impulse response and calculates the average group delay.
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// This represents the initial delay before the most energetic part of the impulse response.
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// The sample-frame delay is removed from the |impulseP| impulse response, and this value is returned.
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// The |length| of the passed in |impulseP| must be must be a power of 2.
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static float extractAverageGroupDelay(float* impulseP, size_t length)
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{
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// Check for power-of-2.
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MOZ_ASSERT(length && (length & (length - 1)) == 0);
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FFTBlock estimationFrame(length);
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estimationFrame.PerformFFT(impulseP);
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float frameDelay = static_cast<float>(estimationFrame.ExtractAverageGroupDelay());
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estimationFrame.GetInverse(impulseP);
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return frameDelay;
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}
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HRTFKernel::HRTFKernel(float* impulseResponse, size_t length, float sampleRate)
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: m_frameDelay(0)
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, m_sampleRate(sampleRate)
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{
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// Determine the leading delay (average group delay) for the response.
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m_frameDelay = extractAverageGroupDelay(impulseResponse, length);
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// The FFT size (with zero padding) needs to be twice the response length
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// in order to do proper convolution.
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unsigned fftSize = 2 * length;
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// Quick fade-out (apply window) at truncation point
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// because the impulse response has been truncated.
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unsigned numberOfFadeOutFrames = static_cast<unsigned>(sampleRate / 4410); // 10 sample-frames @44.1KHz sample-rate
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MOZ_ASSERT(numberOfFadeOutFrames < length);
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if (numberOfFadeOutFrames < length) {
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for (unsigned i = length - numberOfFadeOutFrames; i < length; ++i) {
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float x = 1.0f - static_cast<float>(i - (length - numberOfFadeOutFrames)) / numberOfFadeOutFrames;
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impulseResponse[i] *= x;
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}
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}
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m_fftFrame = new FFTBlock(fftSize);
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m_fftFrame->PadAndMakeScaledDFT(impulseResponse, length);
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}
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// Interpolates two kernels with x: 0 -> 1 and returns the result.
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nsReturnRef<HRTFKernel> HRTFKernel::createInterpolatedKernel(HRTFKernel* kernel1, HRTFKernel* kernel2, float x)
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{
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MOZ_ASSERT(kernel1 && kernel2);
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if (!kernel1 || !kernel2)
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return nsReturnRef<HRTFKernel>();
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MOZ_ASSERT(x >= 0.0 && x < 1.0);
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x = mozilla::clamped(x, 0.0f, 1.0f);
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float sampleRate1 = kernel1->sampleRate();
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float sampleRate2 = kernel2->sampleRate();
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MOZ_ASSERT(sampleRate1 == sampleRate2);
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if (sampleRate1 != sampleRate2)
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return nsReturnRef<HRTFKernel>();
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float frameDelay = (1 - x) * kernel1->frameDelay() + x * kernel2->frameDelay();
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nsAutoPtr<FFTBlock> interpolatedFrame(
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FFTBlock::CreateInterpolatedBlock(*kernel1->fftFrame(), *kernel2->fftFrame(), x));
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return HRTFKernel::create(interpolatedFrame, frameDelay, sampleRate1);
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}
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} // namespace WebCore
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