| /* |
| * Copyright (C) 2013 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: |
| * |
| * * Redistributions of source code must retain the above copyright |
| * notice, this list of conditions and the following disclaimer. |
| * * 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. |
| * * Neither the name of Google Inc. 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 THE COPYRIGHT HOLDERS AND 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 THE COPYRIGHT |
| * OWNER OR 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 |
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| * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE. |
| */ |
| |
| #include "config.h" |
| |
| #if ENABLE(WEB_AUDIO) |
| |
| #include "platform/audio/DownSampler.h" |
| |
| #include "wtf/MathExtras.h" |
| |
| namespace WebCore { |
| |
| DownSampler::DownSampler(size_t inputBlockSize) |
| : m_inputBlockSize(inputBlockSize) |
| , m_reducedKernel(DefaultKernelSize / 2) |
| , m_convolver(inputBlockSize / 2) // runs at 1/2 source sample-rate |
| , m_tempBuffer(inputBlockSize / 2) |
| , m_inputBuffer(inputBlockSize * 2) |
| { |
| initializeKernel(); |
| } |
| |
| void DownSampler::initializeKernel() |
| { |
| // Blackman window parameters. |
| double alpha = 0.16; |
| double a0 = 0.5 * (1.0 - alpha); |
| double a1 = 0.5; |
| double a2 = 0.5 * alpha; |
| |
| int n = DefaultKernelSize; |
| int halfSize = n / 2; |
| |
| // Half-band filter. |
| double sincScaleFactor = 0.5; |
| |
| // Compute only the odd terms because the even ones are zero, except |
| // right in the middle at halfSize, which is 0.5 and we'll handle specially during processing |
| // after doing the main convolution using m_reducedKernel. |
| for (int i = 1; i < n; i += 2) { |
| // Compute the sinc() with offset. |
| double s = sincScaleFactor * piDouble * (i - halfSize); |
| double sinc = !s ? 1.0 : sin(s) / s; |
| sinc *= sincScaleFactor; |
| |
| // Compute Blackman window, matching the offset of the sinc(). |
| double x = static_cast<double>(i) / n; |
| double window = a0 - a1 * cos(2.0 * piDouble * x) + a2 * cos(4.0 * piDouble * x); |
| |
| // Window the sinc() function. |
| // Then store only the odd terms in the kernel. |
| // In a sense, this is shifting forward in time by one sample-frame at the destination sample-rate. |
| m_reducedKernel[(i - 1) / 2] = sinc * window; |
| } |
| } |
| |
| void DownSampler::process(const float* sourceP, float* destP, size_t sourceFramesToProcess) |
| { |
| bool isInputBlockSizeGood = sourceFramesToProcess == m_inputBlockSize; |
| ASSERT(isInputBlockSizeGood); |
| if (!isInputBlockSizeGood) |
| return; |
| |
| size_t destFramesToProcess = sourceFramesToProcess / 2; |
| |
| bool isTempBufferGood = destFramesToProcess == m_tempBuffer.size(); |
| ASSERT(isTempBufferGood); |
| if (!isTempBufferGood) |
| return; |
| |
| bool isReducedKernelGood = m_reducedKernel.size() == DefaultKernelSize / 2; |
| ASSERT(isReducedKernelGood); |
| if (!isReducedKernelGood) |
| return; |
| |
| size_t halfSize = DefaultKernelSize / 2; |
| |
| // Copy source samples to 2nd half of input buffer. |
| bool isInputBufferGood = m_inputBuffer.size() == sourceFramesToProcess * 2 && halfSize <= sourceFramesToProcess; |
| ASSERT(isInputBufferGood); |
| if (!isInputBufferGood) |
| return; |
| |
| float* inputP = m_inputBuffer.data() + sourceFramesToProcess; |
| memcpy(inputP, sourceP, sizeof(float) * sourceFramesToProcess); |
| |
| // Copy the odd sample-frames from sourceP, delayed by one sample-frame (destination sample-rate) |
| // to match shifting forward in time in m_reducedKernel. |
| float* oddSamplesP = m_tempBuffer.data(); |
| for (unsigned i = 0; i < destFramesToProcess; ++i) |
| oddSamplesP[i] = *((inputP - 1) + i * 2); |
| |
| // Actually process oddSamplesP with m_reducedKernel for efficiency. |
| // The theoretical kernel is double this size with 0 values for even terms (except center). |
| m_convolver.process(&m_reducedKernel, oddSamplesP, destP, destFramesToProcess); |
| |
| // Now, account for the 0.5 term right in the middle of the kernel. |
| // This amounts to a delay-line of length halfSize (at the source sample-rate), |
| // scaled by 0.5. |
| |
| // Sum into the destination. |
| for (unsigned i = 0; i < destFramesToProcess; ++i) |
| destP[i] += 0.5 * *((inputP - halfSize) + i * 2); |
| |
| // Copy 2nd half of input buffer to 1st half. |
| memcpy(m_inputBuffer.data(), inputP, sizeof(float) * sourceFramesToProcess); |
| } |
| |
| void DownSampler::reset() |
| { |
| m_convolver.reset(); |
| m_inputBuffer.zero(); |
| } |
| |
| size_t DownSampler::latencyFrames() const |
| { |
| // Divide by two since this is a linear phase kernel and the delay is at the center of the kernel. |
| return m_reducedKernel.size() / 2; |
| } |
| |
| } // namespace WebCore |
| |
| #endif // ENABLE(WEB_AUDIO) |