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78b1c4a487
Letting the delay estimator operate at a sampling frequency of 2 kHz with audio between 0 and 1 kHz makes it sensitive to noisy environments. This CL bandpass filters the 16 kHz signal before downsampling to 2 kHz in a way that the downsampled 2 kHz signal contains audio between 1 and 2 kHz. It also sets downsampling factor 8 as default which significantly reduces computational complexity. Bug: webrtc:9288,chromium:846615 Change-Id: Iaf67898a1a14326cd61bb7f81c14d3c12a697c8d Reviewed-on: https://webrtc-review.googlesource.com/78703 Commit-Queue: Gustaf Ullberg <gustaf@webrtc.org> Reviewed-by: Per Åhgren <peah@webrtc.org> Cr-Commit-Position: refs/heads/master@{#23395}
87 lines
3.3 KiB
C++
87 lines
3.3 KiB
C++
/*
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* Copyright (c) 2017 The WebRTC project authors. All Rights Reserved.
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*
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* Use of this source code is governed by a BSD-style license
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* that can be found in the LICENSE file in the root of the source
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* tree. An additional intellectual property rights grant can be found
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* in the file PATENTS. All contributing project authors may
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* be found in the AUTHORS file in the root of the source tree.
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*/
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#include "modules/audio_processing/aec3/decimator.h"
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#include "rtc_base/checks.h"
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namespace webrtc {
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namespace {
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// b, a = signal.butter(2, 3400/8000.0, 'lowpass', analog=False) which are the
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// same as b, a = signal.butter(2, 1700/4000.0, 'lowpass', analog=False).
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const CascadedBiQuadFilter::BiQuadCoefficients kLowPassFilterCoefficients2 = {
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{0.22711796f, 0.45423593f, 0.22711796f},
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{-0.27666461f, 0.18513647f}};
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constexpr int kNumFilters2 = 3;
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// b, a = signal.butter(2, 1500/8000.0, 'lowpass', analog=False) which are the
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// same as b, a = signal.butter(2, 75/4000.0, 'lowpass', analog=False).
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const CascadedBiQuadFilter::BiQuadCoefficients kLowPassFilterCoefficients4 = {
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{0.0179f, 0.0357f, 0.0179f},
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{-1.5879f, 0.6594f}};
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constexpr int kNumFilters4 = 3;
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// b, a = signal.cheby1(1, 6, [1000/8000, 2000/8000], btype='bandpass',
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// analog=False)
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const CascadedBiQuadFilter::BiQuadCoefficients kBandPassFilterCoefficients8 = {
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{0.10330478f, 0.f, -0.10330478f},
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{-1.520363f, 0.79339043f}};
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constexpr int kNumFilters8 = 5;
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// b, a = signal.butter(2, 1000/8000.0, 'highpass', analog=False)
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const CascadedBiQuadFilter::BiQuadCoefficients kHighPassFilterCoefficients = {
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{0.75707638f, -1.51415275f, 0.75707638f},
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{-1.45424359f, 0.57406192f}};
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constexpr int kNumFiltersHP2 = 1;
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constexpr int kNumFiltersHP4 = 1;
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constexpr int kNumFiltersHP8 = 0;
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} // namespace
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Decimator::Decimator(size_t down_sampling_factor)
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: down_sampling_factor_(down_sampling_factor),
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anti_aliasing_filter_(
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down_sampling_factor_ == 4
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? kLowPassFilterCoefficients4
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: (down_sampling_factor_ == 8 ? kBandPassFilterCoefficients8
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: kLowPassFilterCoefficients2),
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down_sampling_factor_ == 4
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? kNumFilters4
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: (down_sampling_factor_ == 8 ? kNumFilters8 : kNumFilters2)),
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noise_reduction_filter_(
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kHighPassFilterCoefficients,
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down_sampling_factor_ == 4
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? kNumFiltersHP4
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: (down_sampling_factor_ == 8 ? kNumFiltersHP8
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: kNumFiltersHP2)) {
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RTC_DCHECK(down_sampling_factor_ == 2 || down_sampling_factor_ == 4 ||
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down_sampling_factor_ == 8);
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}
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void Decimator::Decimate(rtc::ArrayView<const float> in,
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rtc::ArrayView<float> out) {
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RTC_DCHECK_EQ(kBlockSize, in.size());
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RTC_DCHECK_EQ(kBlockSize / down_sampling_factor_, out.size());
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std::array<float, kBlockSize> x;
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// Limit the frequency content of the signal to avoid aliasing.
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anti_aliasing_filter_.Process(in, x);
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// Reduce the impact of near-end noise.
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noise_reduction_filter_.Process(x);
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// Downsample the signal.
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for (size_t j = 0, k = 0; j < out.size(); ++j, k += down_sampling_factor_) {
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RTC_DCHECK_GT(kBlockSize, k);
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out[j] = x[k];
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}
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}
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} // namespace webrtc
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