modules/audio_processing/agc2/rnn_vad/pitch_search_internal.h

/*
 *  Copyright (c) 2018 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.
 */

#ifndef MODULES_AUDIO_PROCESSING_AGC2_RNN_VAD_PITCH_SEARCH_INTERNAL_H_
#define MODULES_AUDIO_PROCESSING_AGC2_RNN_VAD_PITCH_SEARCH_INTERNAL_H_

#include <array>

#include "api/array_view.h"
#include "common_audio/real_fourier.h"
#include "modules/audio_processing/agc2/rnn_vad/common.h"
#include "modules/audio_processing/agc2/rnn_vad/pitch_info.h"

namespace webrtc {
namespace rnn_vad {

// The inverted lags for the pitch interval [|kInitialMinPitch12kHz|,
// |kMaxPitch12kHz|] are in the range [0, |kNumInvertedLags|].
static_assert(kMaxPitch12kHz > kInitialMinPitch12kHz, "");
static_assert(kMaxPitch24kHz > kInitialMinPitch24kHz, "");
constexpr size_t kNumInvertedLags12kHz = kMaxPitch12kHz - kInitialMinPitch12kHz;
constexpr size_t kNumInvertedLags24kHz = kMaxPitch24kHz - kInitialMinPitch24kHz;
constexpr int kAutoCorrelationFftOrder = 9;  // Length-512 FFT.

static_assert(1 << kAutoCorrelationFftOrder >
                  kNumInvertedLags12kHz + kBufSize12kHz - kMaxPitch12kHz,
              "");

// Performs 2x decimation without any anti-aliasing filter.
void Decimate2x(rtc::ArrayView<const float, kBufSize24kHz> src,
                rtc::ArrayView<float, kBufSize12kHz> dst);

// Computes a gain threshold for a candidate pitch period given the initial and
// the previous pitch period and gain estimates and the pitch period ratio used
// to derive the candidate pitch period from the initial period.
float ComputePitchGainThreshold(size_t candidate_pitch_period,
                                size_t pitch_period_ratio,
                                size_t initial_pitch_period,
                                float initial_pitch_gain,
                                size_t prev_pitch_period,
                                size_t prev_pitch_gain);

// Computes the sum of squared samples for every sliding frame in the pitch
// buffer. |yy_values| indexes are lags.
//
// The pitch buffer is structured as depicted below:
// |.........|...........|
//      a          b
// The part on the left, named "a" contains the oldest samples, whereas "b" the
// most recent ones. The size of "a" corresponds to the maximum pitch period,
// that of "b" to the frame size (e.g., 16 ms and 20 ms respectively).
void ComputeSlidingFrameSquareEnergies(
    rtc::ArrayView<const float, kBufSize24kHz> pitch_buf,
    rtc::ArrayView<float, kMaxPitch24kHz + 1> yy_values);

// Computes the auto-correlation coefficients for a given pitch interval.
// |auto_corr| indexes are inverted lags.
//
// 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 ComputePitchAutoCorrelation(
    rtc::ArrayView<const float, kBufSize12kHz> pitch_buf,
    size_t max_pitch_period,
    rtc::ArrayView<float, kNumInvertedLags12kHz> auto_corr,
    webrtc::RealFourier* fft);

// Given the auto-correlation coefficients stored according to
// ComputePitchAutoCorrelation() (i.e., using inverted lags), returns the best
// and the second best pitch periods.
std::array<size_t, 2> FindBestPitchPeriods(
    rtc::ArrayView<const float> auto_corr,
    rtc::ArrayView<const float> pitch_buf,
    size_t max_pitch_period);

// Refines the pitch period estimation given the pitch buffer |pitch_buf| and
// the initial pitch period estimation |inv_lags|. Returns an inverted lag at
// 48 kHz.
size_t RefinePitchPeriod48kHz(
    rtc::ArrayView<const float, kBufSize24kHz> pitch_buf,
    rtc::ArrayView<const size_t, 2> inv_lags);

// Refines the pitch period estimation and compute the pitch gain. Returns the
// refined pitch estimation data at 48 kHz.
PitchInfo CheckLowerPitchPeriodsAndComputePitchGain(
    rtc::ArrayView<const float, kBufSize24kHz> pitch_buf,
    size_t initial_pitch_period_48kHz,
    PitchInfo prev_pitch_48kHz);

}  // namespace rnn_vad
}  // namespace webrtc

#endif  // MODULES_AUDIO_PROCESSING_AGC2_RNN_VAD_PITCH_SEARCH_INTERNAL_H_