1/* 2 * Copyright (C) 2013 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 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 "config.h" 30 31#if ENABLE(WEB_AUDIO) 32 33#include "DownSampler.h" 34 35#include <wtf/MathExtras.h> 36 37namespace WebCore { 38 39DownSampler::DownSampler(size_t inputBlockSize) 40 : m_inputBlockSize(inputBlockSize) 41 , m_reducedKernel(DefaultKernelSize / 2) 42 , m_convolver(inputBlockSize / 2) // runs at 1/2 source sample-rate 43 , m_tempBuffer(inputBlockSize / 2) 44 , m_inputBuffer(inputBlockSize * 2) 45{ 46 initializeKernel(); 47} 48 49void DownSampler::initializeKernel() 50{ 51 // Blackman window parameters. 52 double alpha = 0.16; 53 double a0 = 0.5 * (1.0 - alpha); 54 double a1 = 0.5; 55 double a2 = 0.5 * alpha; 56 57 int n = DefaultKernelSize; 58 int halfSize = n / 2; 59 60 // Half-band filter. 61 double sincScaleFactor = 0.5; 62 63 // Compute only the odd terms because the even ones are zero, except 64 // right in the middle at halfSize, which is 0.5 and we'll handle specially during processing 65 // after doing the main convolution using m_reducedKernel. 66 for (int i = 1; i < n; i += 2) { 67 // Compute the sinc() with offset. 68 double s = sincScaleFactor * piDouble * (i - halfSize); 69 double sinc = !s ? 1.0 : sin(s) / s; 70 sinc *= sincScaleFactor; 71 72 // Compute Blackman window, matching the offset of the sinc(). 73 double x = static_cast<double>(i) / n; 74 double window = a0 - a1 * cos(2.0 * piDouble * x) + a2 * cos(4.0 * piDouble * x); 75 76 // Window the sinc() function. 77 // Then store only the odd terms in the kernel. 78 // In a sense, this is shifting forward in time by one sample-frame at the destination sample-rate. 79 m_reducedKernel[(i - 1) / 2] = sinc * window; 80 } 81} 82 83void DownSampler::process(const float* sourceP, float* destP, size_t sourceFramesToProcess) 84{ 85 bool isInputBlockSizeGood = sourceFramesToProcess == m_inputBlockSize; 86 ASSERT(isInputBlockSizeGood); 87 if (!isInputBlockSizeGood) 88 return; 89 90 size_t destFramesToProcess = sourceFramesToProcess / 2; 91 92 bool isTempBufferGood = destFramesToProcess == m_tempBuffer.size(); 93 ASSERT(isTempBufferGood); 94 if (!isTempBufferGood) 95 return; 96 97 bool isReducedKernelGood = m_reducedKernel.size() == DefaultKernelSize / 2; 98 ASSERT(isReducedKernelGood); 99 if (!isReducedKernelGood) 100 return; 101 102 size_t halfSize = DefaultKernelSize / 2; 103 104 // Copy source samples to 2nd half of input buffer. 105 bool isInputBufferGood = m_inputBuffer.size() == sourceFramesToProcess * 2 && halfSize <= sourceFramesToProcess; 106 ASSERT(isInputBufferGood); 107 if (!isInputBufferGood) 108 return; 109 110 float* inputP = m_inputBuffer.data() + sourceFramesToProcess; 111 memcpy(inputP, sourceP, sizeof(float) * sourceFramesToProcess); 112 113 // Copy the odd sample-frames from sourceP, delayed by one sample-frame (destination sample-rate) 114 // to match shifting forward in time in m_reducedKernel. 115 float* oddSamplesP = m_tempBuffer.data(); 116 for (unsigned i = 0; i < destFramesToProcess; ++i) 117 oddSamplesP[i] = *((inputP - 1) + i * 2); 118 119 // Actually process oddSamplesP with m_reducedKernel for efficiency. 120 // The theoretical kernel is double this size with 0 values for even terms (except center). 121 m_convolver.process(&m_reducedKernel, oddSamplesP, destP, destFramesToProcess); 122 123 // Now, account for the 0.5 term right in the middle of the kernel. 124 // This amounts to a delay-line of length halfSize (at the source sample-rate), 125 // scaled by 0.5. 126 127 // Sum into the destination. 128 for (unsigned i = 0; i < destFramesToProcess; ++i) 129 destP[i] += 0.5 * *((inputP - halfSize) + i * 2); 130 131 // Copy 2nd half of input buffer to 1st half. 132 memcpy(m_inputBuffer.data(), inputP, sizeof(float) * sourceFramesToProcess); 133} 134 135void DownSampler::reset() 136{ 137 m_convolver.reset(); 138 m_inputBuffer.zero(); 139} 140 141size_t DownSampler::latencyFrames() const 142{ 143 // Divide by two since this is a linear phase kernel and the delay is at the center of the kernel. 144 return m_reducedKernel.size() / 2; 145} 146 147} // namespace WebCore 148 149#endif // ENABLE(WEB_AUDIO) 150