435187d18d
CascadedBiQuadFilter can run identical filters multiple times. This CL allows the use of different filters in each step. This enables the use of more elaborate filters. The filters are defined by zeros, poles and gains. The 'old' way of initializing CascadedBiQuadFilter with a transfer function and number of filters is left intact. Bug: webrtc:9288,chromium:846615 Change-Id: Ie4a5b98eba044415571cdcac087b20870a0b5d33 Reviewed-on: https://webrtc-review.googlesource.com/80060 Reviewed-by: Per Åhgren <peah@webrtc.org> Commit-Queue: Gustaf Ullberg <gustaf@webrtc.org> Cr-Commit-Position: refs/heads/master@{#23473}
88 lines
3.3 KiB
C++
88 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, 750/8000.0, 'lowpass', analog=False) which are the
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// same as b, a = signal.butter(2, 375/4000.0, '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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