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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 <cstddef>
#include "api/array_view.h"
#include "modules/audio_processing/aec3/aec3_common.h"
#include "modules/audio_processing/utility/cascaded_biquad_filter.h"
#include "rtc_base/checks.h"
namespace webrtc {
namespace {
// signal.ellip(6, 1, 40, 1800/8000, 'lowpass', output='sos')
constexpr std::array<CascadedBiQuadFilter::BiQuadCoefficients, 3>
kLowPassFilterDs4 = {{
{{0.0180919877f, 0.00320961363f, 0.0180919877f},
{-1.5183195f, 0.633165865f}},
{{1.0f, -1.24550459f, 1.0f}, {-1.49784254f, 0.853586692f}},
{{1.0f, -1.4221681f, 1.0f}, {-1.49791282f, 0.969572384f}},
}};
// signal.cheby1(1, 6, [1000/8000, 2000/8000], 'bandpass', output='sos')
// repeated 5 times.
constexpr std::array<CascadedBiQuadFilter::BiQuadCoefficients, 5>
kBandPassFilterDs8 = {{
{{0.103304783f, 0.0f, -0.103304783f}, {-1.520363f, 0.793390435f}},
{{0.103304783f, 0.0f, -0.103304783f}, {-1.520363f, 0.793390435f}},
{{0.103304783f, 0.0f, -0.103304783f}, {-1.520363f, 0.793390435f}},
{{0.103304783f, 0.0f, -0.103304783f}, {-1.520363f, 0.793390435f}},
{{0.103304783f, 0.0f, -0.103304783f}, {-1.520363f, 0.793390435f}},
}};
// signal.butter(2, 1000/8000.0, 'highpass', output='sos')
constexpr std::array<CascadedBiQuadFilter::BiQuadCoefficients, 1>
kHighPassFilter = {{
{{0.757076375f, -1.51415275f, 0.757076375f},
{-1.45424359f, 0.574061915f}},
}};
constexpr std::array<CascadedBiQuadFilter::BiQuadCoefficients, 0>
kPassThroughFilter = {{}};
} // namespace
Decimator::Decimator(size_t down_sampling_factor)
: down_sampling_factor_(down_sampling_factor),
anti_aliasing_filter_(
down_sampling_factor_ == 4
? ArrayView<const CascadedBiQuadFilter::BiQuadCoefficients>(
kLowPassFilterDs4)
: ArrayView<const CascadedBiQuadFilter::BiQuadCoefficients>(
kBandPassFilterDs8)),
noise_reduction_filter_(
down_sampling_factor_ == 8
? (ArrayView<const CascadedBiQuadFilter::BiQuadCoefficients>(
kPassThroughFilter))
: (ArrayView<const CascadedBiQuadFilter::BiQuadCoefficients>(
kHighPassFilter))) {
RTC_DCHECK(down_sampling_factor_ == 4 || down_sampling_factor_ == 8);
}
void Decimator::Decimate(ArrayView<const float> in, 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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