decimator.cc (3555B)
1 /* 2 * Copyright (c) 2017 The WebRTC project authors. All Rights Reserved. 3 * 4 * Use of this source code is governed by a BSD-style license 5 * that can be found in the LICENSE file in the root of the source 6 * tree. An additional intellectual property rights grant can be found 7 * in the file PATENTS. All contributing project authors may 8 * be found in the AUTHORS file in the root of the source tree. 9 */ 10 #include "modules/audio_processing/aec3/decimator.h" 11 12 #include <array> 13 #include <cstddef> 14 15 #include "api/array_view.h" 16 #include "modules/audio_processing/aec3/aec3_common.h" 17 #include "modules/audio_processing/utility/cascaded_biquad_filter.h" 18 #include "rtc_base/checks.h" 19 20 namespace webrtc { 21 namespace { 22 // signal.ellip(6, 1, 40, 1800/8000, 'lowpass', output='sos') 23 constexpr std::array<CascadedBiQuadFilter::BiQuadCoefficients, 3> 24 kLowPassFilterDs4 = {{ 25 {.b = {0.0180919877f, 0.00320961363f, 0.0180919877f}, 26 .a = {-1.5183195f, 0.633165865f}}, 27 {.b = {1.0f, -1.24550459f, 1.0f}, .a = {-1.49784254f, 0.853586692f}}, 28 {.b = {1.0f, -1.4221681f, 1.0f}, .a = {-1.49791282f, 0.969572384f}}, 29 }}; 30 31 // signal.cheby1(1, 6, [1000/8000, 2000/8000], 'bandpass', output='sos') 32 // repeated 5 times. 33 constexpr std::array<CascadedBiQuadFilter::BiQuadCoefficients, 5> 34 kBandPassFilterDs8 = {{ 35 {.b = {0.103304783f, 0.0f, -0.103304783f}, 36 .a = {-1.520363f, 0.793390435f}}, 37 {.b = {0.103304783f, 0.0f, -0.103304783f}, 38 .a = {-1.520363f, 0.793390435f}}, 39 {.b = {0.103304783f, 0.0f, -0.103304783f}, 40 .a = {-1.520363f, 0.793390435f}}, 41 {.b = {0.103304783f, 0.0f, -0.103304783f}, 42 .a = {-1.520363f, 0.793390435f}}, 43 {.b = {0.103304783f, 0.0f, -0.103304783f}, 44 .a = {-1.520363f, 0.793390435f}}, 45 }}; 46 47 // signal.butter(2, 1000/8000.0, 'highpass', output='sos') 48 constexpr std::array<CascadedBiQuadFilter::BiQuadCoefficients, 1> 49 kHighPassFilter = {{ 50 {.b = {0.757076375f, -1.51415275f, 0.757076375f}, 51 .a = {-1.45424359f, 0.574061915f}}, 52 }}; 53 54 constexpr std::array<CascadedBiQuadFilter::BiQuadCoefficients, 0> 55 kPassThroughFilter = {{}}; 56 } // namespace 57 58 Decimator::Decimator(size_t down_sampling_factor) 59 : down_sampling_factor_(down_sampling_factor), 60 anti_aliasing_filter_( 61 down_sampling_factor_ == 4 62 ? ArrayView<const CascadedBiQuadFilter::BiQuadCoefficients>( 63 kLowPassFilterDs4) 64 : ArrayView<const CascadedBiQuadFilter::BiQuadCoefficients>( 65 kBandPassFilterDs8)), 66 noise_reduction_filter_( 67 down_sampling_factor_ == 8 68 ? (ArrayView<const CascadedBiQuadFilter::BiQuadCoefficients>( 69 kPassThroughFilter)) 70 : (ArrayView<const CascadedBiQuadFilter::BiQuadCoefficients>( 71 kHighPassFilter))) { 72 RTC_DCHECK(down_sampling_factor_ == 4 || down_sampling_factor_ == 8); 73 } 74 75 void Decimator::Decimate(ArrayView<const float> in, ArrayView<float> out) { 76 RTC_DCHECK_EQ(kBlockSize, in.size()); 77 RTC_DCHECK_EQ(kBlockSize / down_sampling_factor_, out.size()); 78 std::array<float, kBlockSize> x; 79 80 // Limit the frequency content of the signal to avoid aliasing. 81 anti_aliasing_filter_.Process(in, x); 82 83 // Reduce the impact of near-end noise. 84 noise_reduction_filter_.Process(x); 85 86 // Downsample the signal. 87 for (size_t j = 0, k = 0; j < out.size(); ++j, k += down_sampling_factor_) { 88 RTC_DCHECK_GT(kBlockSize, k); 89 out[j] = x[k]; 90 } 91 } 92 93 } // namespace webrtc