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