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Side by Side Diff: Source/core/platform/audio/UpSampler.cpp

Issue 15619003: Add support for WaveShaperNode.oversample (Closed) Base URL: svn://svn.chromium.org/blink/trunk
Patch Set: thread-safety Created 7 years, 7 months ago
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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 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 "config.h"
30
31 #if ENABLE(WEB_AUDIO)
32
33 #include "core/platform/audio/UpSampler.h"
34
35 #include "wtf/MathExtras.h"
36
37 namespace WebCore {
38
39 UpSampler::UpSampler(size_t inputBlockSize)
40 : m_inputBlockSize(inputBlockSize)
41 , m_kernel(DefaultKernelSize)
42 , m_tempBuffer(inputBlockSize)
43 , m_inputBuffer(inputBlockSize * 2)
44 , m_convolver(inputBlockSize)
45 {
46 initializeKernel();
47 }
48
49 void UpSampler::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 = m_kernel.size();
58 int halfSize = n / 2;
59 double subsampleOffset = -0.5;
60
61 for (int i = 0; i < n; ++i) {
62 // Compute the sinc() with offset.
63 double s = piDouble * (i - halfSize - subsampleOffset);
64 double sinc = !s ? 1.0 : sin(s) / s;
65
66 // Compute Blackman window, matching the offset of the sinc().
67 double x = (i - subsampleOffset) / n;
68 double window = a0 - a1 * cos(2.0 * piDouble * x) + a2 * cos(4.0 * piDou ble * x);
69
70 // Window the sinc() function.
71 m_kernel[i] = sinc * window;
72 }
73 }
74
75 void UpSampler::process(const float* sourceP, float* destP, size_t sourceFramesT oProcess)
76 {
77 ASSERT(sourceFramesToProcess == m_tempBuffer.size());
78 if (sourceFramesToProcess != m_tempBuffer.size())
79 return;
80
81 // Copy source samples to 2nd half of input buffer.
82 float* inputP = m_inputBuffer.data() + m_inputBlockSize;
83 memcpy(inputP, sourceP, sizeof(float) * sourceFramesToProcess);
84
85 int halfSize = m_kernel.size() / 2;
86
87 // Copy even sample-frames 0,2,4,6... (delayed by the linear phase delay) di rectly into destP.
88 for (unsigned i = 0; i < sourceFramesToProcess; ++i)
89 destP[i * 2] = inputP[i - halfSize];
Ken Russell (switch to Gerrit) 2013/05/23 02:29:25 Checks and assertions are needed to ensure that "i
Chris Rogers 2013/05/24 20:09:04 Done.
90
91 // Compute odd sample-frames 1,3,5,7...
92 float* oddSamplesP = m_tempBuffer.data();
93 m_convolver.process(&m_kernel, sourceP, oddSamplesP, sourceFramesToProcess);
94
95 for (unsigned i = 0; i < sourceFramesToProcess; ++i)
96 destP[i * 2 + 1] = oddSamplesP[i];
97
98 // Copy 2nd half of input buffer to 1st half.
99 memcpy(m_inputBuffer.data(), inputP, sizeof(float) * sourceFramesToProcess);
Ken Russell (switch to Gerrit) 2013/05/23 02:29:25 Again could you please explain to me why m_inputBu
Chris Rogers 2013/05/24 20:09:04 Added comment in header file.
100 }
101
102 void UpSampler::reset()
103 {
104 m_convolver.reset();
105 m_inputBuffer.zero();
106 }
107
108 size_t UpSampler::latencyFrames() const
109 {
110 // Divide by two since this is a linear phase kernel and the delay is at the center of the kernel.
111 return m_kernel.size() / 2;
112 }
113
114 } // namespace WebCore
115
116 #endif // ENABLE(WEB_AUDIO)
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