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1 /* | 1 /* |
2 * Copyright (C) 2013 Google Inc. All rights reserved. | 2 * Copyright (C) 2013 Google Inc. All rights reserved. |
3 * | 3 * |
4 * Redistribution and use in source and binary forms, with or without | 4 * Redistribution and use in source and binary forms, with or without |
5 * modification, are permitted provided that the following conditions are | 5 * modification, are permitted provided that the following conditions are |
6 * met: | 6 * met: |
7 * | 7 * |
8 * * Redistributions of source code must retain the above copyright | 8 * * Redistributions of source code must retain the above copyright |
9 * notice, this list of conditions and the following disclaimer. | 9 * notice, this list of conditions and the following disclaimer. |
10 * * Redistributions in binary form must reproduce the above | 10 * * Redistributions in binary form must reproduce the above |
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29 */ | 29 */ |
30 | 30 |
31 #include "platform/audio/DownSampler.h" | 31 #include "platform/audio/DownSampler.h" |
32 #include "wtf/MathExtras.h" | 32 #include "wtf/MathExtras.h" |
33 | 33 |
34 namespace blink { | 34 namespace blink { |
35 | 35 |
36 DownSampler::DownSampler(size_t inputBlockSize) | 36 DownSampler::DownSampler(size_t inputBlockSize) |
37 : m_inputBlockSize(inputBlockSize), | 37 : m_inputBlockSize(inputBlockSize), |
38 m_reducedKernel(DefaultKernelSize / 2), | 38 m_reducedKernel(DefaultKernelSize / 2), |
39 m_convolver(inputBlockSize / 2) // runs at 1/2 source sample-rate | 39 m_convolver(inputBlockSize / 2), // runs at 1/2 source sample-rate |
40 , | |
41 m_tempBuffer(inputBlockSize / 2), | 40 m_tempBuffer(inputBlockSize / 2), |
42 m_inputBuffer(inputBlockSize * 2) { | 41 m_inputBuffer(inputBlockSize * 2) { |
43 initializeKernel(); | 42 initializeKernel(); |
44 } | 43 } |
45 | 44 |
46 void DownSampler::initializeKernel() { | 45 void DownSampler::initializeKernel() { |
47 // Blackman window parameters. | 46 // Blackman window parameters. |
48 double alpha = 0.16; | 47 double alpha = 0.16; |
49 double a0 = 0.5 * (1.0 - alpha); | 48 double a0 = 0.5 * (1.0 - alpha); |
50 double a1 = 0.5; | 49 double a1 = 0.5; |
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140 m_inputBuffer.zero(); | 139 m_inputBuffer.zero(); |
141 } | 140 } |
142 | 141 |
143 size_t DownSampler::latencyFrames() const { | 142 size_t DownSampler::latencyFrames() const { |
144 // Divide by two since this is a linear phase kernel and the delay is at the | 143 // Divide by two since this is a linear phase kernel and the delay is at the |
145 // center of the kernel. | 144 // center of the kernel. |
146 return m_reducedKernel.size() / 2; | 145 return m_reducedKernel.size() / 2; |
147 } | 146 } |
148 | 147 |
149 } // namespace blink | 148 } // namespace blink |
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