OLD | NEW |
---|---|
(Empty) | |
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) | |
OLD | NEW |