chromium/third_party/webrtc/modules/audio_processing/agc2/rnn_vad/auto_correlation.cc

/*
 *  Copyright (c) 2019 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/agc2/rnn_vad/auto_correlation.h"

#include <algorithm>

#include "rtc_base/checks.h"

namespace webrtc {
namespace rnn_vad {
namespace {

constexpr int kAutoCorrelationFftOrder = …;  // Length-512 FFT.
static_assert …;

}  // namespace

AutoCorrelationCalculator::AutoCorrelationCalculator()
    : … { … }

AutoCorrelationCalculator::~AutoCorrelationCalculator() = default;

// The auto-correlations coefficients are computed as follows:
// |.........|...........|  <- pitch buffer
//           [ x (fixed) ]
// [   y_0   ]
//         [ y_{m-1} ]
// x and y are sub-array of equal length; x is never moved, whereas y slides.
// The cross-correlation between y_0 and x corresponds to the auto-correlation
// for the maximum pitch period. Hence, the first value in `auto_corr` has an
// inverted lag equal to 0 that corresponds to a lag equal to the maximum
// pitch period.
void AutoCorrelationCalculator::ComputeOnPitchBuffer(
    rtc::ArrayView<const float, kBufSize12kHz> pitch_buf,
    rtc::ArrayView<float, kNumLags12kHz> auto_corr) { … }

}  // namespace rnn_vad
}  // namespace webrtc