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/*
* Copyright (c) 2017 The WebRTC project authors. All Rights Reserved.
*
* Use of this source code is governed by a BSD-style license
* that can be found in the LICENSE file in the root of the source
* tree. An additional intellectual property rights grant can be found
* in the file PATENTS. All contributing project authors may
* be found in the AUTHORS file in the root of the source tree.
*/
#include "modules/audio_processing/aec3/decimator.h"
#include <array>
#include <vector>
#include "modules/audio_processing/aec3/aec3_common.h"
#include "rtc_base/checks.h"
namespace webrtc {
namespace {
// signal.butter(2, 3400/8000.0, 'lowpass', analog=False)
const std::vector<CascadedBiQuadFilter::BiQuadParam> GetLowPassFilterDS2() {
return std::vector<CascadedBiQuadFilter::BiQuadParam>{
{{-1.f, 0.f}, {0.13833231f, 0.40743176f}, 0.22711796393486466f},
{{-1.f, 0.f}, {0.13833231f, 0.40743176f}, 0.22711796393486466f},
{{-1.f, 0.f}, {0.13833231f, 0.40743176f}, 0.22711796393486466f}};
}
// signal.ellip(6, 1, 40, 1800/8000, btype='lowpass', analog=False)
const std::vector<CascadedBiQuadFilter::BiQuadParam> GetLowPassFilterDS4() {
return std::vector<CascadedBiQuadFilter::BiQuadParam>{
{{-0.08873842f, 0.99605496f}, {0.75916227f, 0.23841065f}, 0.26250696827f},
{{0.62273832f, 0.78243018f}, {0.74892112f, 0.5410152f}, 0.26250696827f},
{{0.71107693f, 0.70311421f}, {0.74895534f, 0.63924616f}, 0.26250696827f}};
}
// signal.cheby1(1, 6, [1000/8000, 2000/8000], btype='bandpass', analog=False)
const std::vector<CascadedBiQuadFilter::BiQuadParam> GetBandPassFilterDS8() {
return std::vector<CascadedBiQuadFilter::BiQuadParam>{
{{1.f, 0.f}, {0.7601815f, 0.46423542f}, 0.10330478266505948f, true},
{{1.f, 0.f}, {0.7601815f, 0.46423542f}, 0.10330478266505948f, true},
{{1.f, 0.f}, {0.7601815f, 0.46423542f}, 0.10330478266505948f, true},
{{1.f, 0.f}, {0.7601815f, 0.46423542f}, 0.10330478266505948f, true},
{{1.f, 0.f}, {0.7601815f, 0.46423542f}, 0.10330478266505948f, true}};
}
// signal.butter(2, 1000/8000.0, 'highpass', analog=False)
const std::vector<CascadedBiQuadFilter::BiQuadParam> GetHighPassFilter() {
return std::vector<CascadedBiQuadFilter::BiQuadParam>{
{{1.f, 0.f}, {0.72712179f, 0.21296904f}, 0.7570763753338849f}};
}
const std::vector<CascadedBiQuadFilter::BiQuadParam> GetPassThroughFilter() {
return std::vector<CascadedBiQuadFilter::BiQuadParam>{};
}
} // namespace
Decimator::Decimator(size_t down_sampling_factor)
: down_sampling_factor_(down_sampling_factor),
anti_aliasing_filter_(down_sampling_factor_ == 4
? GetLowPassFilterDS4()
: (down_sampling_factor_ == 8
? GetBandPassFilterDS8()
: GetLowPassFilterDS2())),
noise_reduction_filter_(down_sampling_factor_ == 8
? GetPassThroughFilter()
: GetHighPassFilter()) {
RTC_DCHECK(down_sampling_factor_ == 2 || down_sampling_factor_ == 4 ||
down_sampling_factor_ == 8);
}
void Decimator::Decimate(rtc::ArrayView<const float> in,
rtc::ArrayView<float> out) {
RTC_DCHECK_EQ(kBlockSize, in.size());
RTC_DCHECK_EQ(kBlockSize / down_sampling_factor_, out.size());
std::array<float, kBlockSize> x;
// Limit the frequency content of the signal to avoid aliasing.
anti_aliasing_filter_.Process(in, x);
// Reduce the impact of near-end noise.
noise_reduction_filter_.Process(x);
// Downsample the signal.
for (size_t j = 0, k = 0; j < out.size(); ++j, k += down_sampling_factor_) {
RTC_DCHECK_GT(kBlockSize, k);
out[j] = x[k];
}
}
} // namespace webrtc
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