blob: 0db3b8f842ea2dc4fa2a4a15599368fc9a6f1746 [file] [log] [blame]
/*
* 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_by_4.h"
#include "rtc_base/checks.h"
namespace webrtc {
namespace {
// [B,A] = butter(2,1500/16000) which are the same as [B,A] =
// butter(2,750/8000).
const CascadedBiQuadFilter::BiQuadCoefficients kLowPassFilterCoefficients = {
{0.0179f, 0.0357f, 0.0179f},
{-1.5879f, 0.6594f}};
} // namespace
DecimatorBy4::DecimatorBy4()
: low_pass_filter_(kLowPassFilterCoefficients, 3) {}
void DecimatorBy4::Decimate(rtc::ArrayView<const float> in,
rtc::ArrayView<float> out) {
RTC_DCHECK_EQ(kBlockSize, in.size());
RTC_DCHECK_EQ(kSubBlockSize, out.size());
std::array<float, kBlockSize> x;
// Limit the frequency content of the signal to avoid aliasing.
low_pass_filter_.Process(in, x);
// Downsample the signal.
for (size_t j = 0, k = 0; j < out.size(); ++j, k += 4) {
RTC_DCHECK_GT(kBlockSize, k);
out[j] = x[k];
}
}
} // namespace webrtc