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The Tor Browser
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HRTFKernel.cpp (4684B)

      1 /*
      2 * Copyright (C) 2010 Google Inc. All rights reserved.
      3 *
      4 * Redistribution and use in source and binary forms, with or without
      5 * modification, are permitted provided that the following conditions
      6 * are met:
      7 *
      8 * 1.  Redistributions of source code must retain the above copyright
      9 *     notice, this list of conditions and the following disclaimer.
     10 * 2.  Redistributions in binary form must reproduce the above copyright
     11 *     notice, this list of conditions and the following disclaimer in the
     12 *     documentation and/or other materials provided with the distribution.
     13 * 3.  Neither the name of Apple Computer, Inc. ("Apple") nor the names of
     14 *     its contributors may be used to endorse or promote products derived
     15 *     from this software without specific prior written permission.
     16 *
     17 * THIS SOFTWARE IS PROVIDED BY APPLE AND ITS CONTRIBUTORS "AS IS" AND ANY
     18 * EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED
     19 * WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
     20 * DISCLAIMED. IN NO EVENT SHALL APPLE OR ITS CONTRIBUTORS BE LIABLE FOR ANY
     21 * DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES
     22 * (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
     23 * LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND
     24 * ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
     25 * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
     26 * THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
     27 */
     28 
     29 #include "HRTFKernel.h"
     30 namespace WebCore {
     31 
     32 // Takes the input audio channel |impulseP| as an input impulse response and
     33 // calculates the average group delay. This represents the initial delay before
     34 // the most energetic part of the impulse response. The sample-frame delay is
     35 // removed from the |impulseP| impulse response, and this value  is returned.
     36 // The |length| of the passed in |impulseP| must be must be a power of 2.
     37 static float extractAverageGroupDelay(float* impulseP, size_t length) {
     38  // Check for power-of-2.
     39  MOZ_ASSERT(length && (length & (length - 1)) == 0);
     40 
     41  FFTBlock estimationFrame(length, 1.f / length);
     42  estimationFrame.PerformFFT(impulseP);
     43 
     44  float frameDelay =
     45      static_cast<float>(estimationFrame.ExtractAverageGroupDelay());
     46  estimationFrame.GetInverse(impulseP);
     47 
     48  return frameDelay;
     49 }
     50 
     51 HRTFKernel::HRTFKernel(float* impulseResponse, size_t length, float sampleRate)
     52    : m_frameDelay(0), m_sampleRate(sampleRate) {
     53  AlignedTArray<float> buffer;
     54  // copy to a 32-byte aligned buffer
     55  if (((uintptr_t)impulseResponse & 31) != 0) {
     56    buffer.SetLength(length);
     57    mozilla::PodCopy(buffer.Elements(), impulseResponse, length);
     58    impulseResponse = buffer.Elements();
     59  }
     60 
     61  // Determine the leading delay (average group delay) for the response.
     62  m_frameDelay = extractAverageGroupDelay(impulseResponse, length);
     63 
     64  // The FFT size (with zero padding) needs to be twice the response length
     65  // in order to do proper convolution.
     66  unsigned fftSize = 2 * length;
     67 
     68  // Quick fade-out (apply window) at truncation point
     69  // because the impulse response has been truncated.
     70  unsigned numberOfFadeOutFrames = static_cast<unsigned>(
     71      sampleRate / 4410);  // 10 sample-frames @44.1KHz sample-rate
     72  MOZ_ASSERT(numberOfFadeOutFrames < length);
     73  if (numberOfFadeOutFrames < length) {
     74    for (unsigned i = length - numberOfFadeOutFrames; i < length; ++i) {
     75      float x =
     76          1.0f - static_cast<float>(i - (length - numberOfFadeOutFrames)) /
     77                     numberOfFadeOutFrames;
     78      impulseResponse[i] *= x;
     79    }
     80  }
     81 
     82  m_fftFrame = mozilla::MakeUnique<FFTBlock>(fftSize);
     83  m_fftFrame->PadAndMakeScaledDFT(impulseResponse, length);
     84 }
     85 
     86 // Interpolates two kernels with x: 0 -> 1 and returns the result.
     87 nsReturnRef<HRTFKernel> HRTFKernel::createInterpolatedKernel(
     88    HRTFKernel* kernel1, HRTFKernel* kernel2, float x) {
     89  MOZ_ASSERT(kernel1 && kernel2);
     90  if (!kernel1 || !kernel2) return nsReturnRef<HRTFKernel>();
     91 
     92  MOZ_ASSERT(x >= 0.0 && x < 1.0);
     93  x = std::clamp(x, 0.0f, 1.0f);
     94 
     95  float sampleRate1 = kernel1->sampleRate();
     96  float sampleRate2 = kernel2->sampleRate();
     97  MOZ_ASSERT(sampleRate1 == sampleRate2);
     98  if (sampleRate1 != sampleRate2) return nsReturnRef<HRTFKernel>();
     99 
    100  float frameDelay =
    101      (1 - x) * kernel1->frameDelay() + x * kernel2->frameDelay();
    102 
    103  UniquePtr<FFTBlock> interpolatedFrame(FFTBlock::CreateInterpolatedBlock(
    104      *kernel1->fftFrame(), *kernel2->fftFrame(), x));
    105  return HRTFKernel::create(std::move(interpolatedFrame), frameDelay,
    106                            sampleRate1);
    107 }
    108 
    109 }  // namespace WebCore