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/*
* 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_SPECTRAL_FEATURES_INTERNAL_H_
#define MODULES_AUDIO_PROCESSING_AGC2_RNN_VAD_SPECTRAL_FEATURES_INTERNAL_H_
#include <stddef.h>
#include <array>
#include <vector>
#include "api/array_view.h"
#include "modules/audio_processing/agc2/rnn_vad/common.h"
namespace webrtc {
namespace rnn_vad {
// At a sample rate of 24 kHz, the last 3 Opus bands are beyond the Nyquist
// frequency. However, band #19 gets the contributions from band #18 because
// of the symmetric triangular filter with peak response at 12 kHz.
constexpr int kOpusBands24kHz = 20;
static_assert(kOpusBands24kHz < kNumBands,
"The number of bands at 24 kHz must be less than those defined "
"in the Opus scale at 48 kHz.");
// Number of FFT frequency bins covered by each band in the Opus scale at a
// sample rate of 24 kHz for 20 ms frames.
// Declared here for unit testing.
constexpr std::array<int, kOpusBands24kHz - 1> GetOpusScaleNumBins24kHz20ms() {
return {4, 4, 4, 4, 4, 4, 4, 4, 8, 8, 8, 8, 16, 16, 16, 24, 24, 32, 48};
}
// TODO(bugs.webrtc.org/10480): Move to a separate file.
// Class to compute band-wise spectral features in the Opus perceptual scale
// for 20 ms frames sampled at 24 kHz. The analysis methods apply triangular
// filters with peak response at the each band boundary.
class SpectralCorrelator {
public:
// Ctor.
SpectralCorrelator();
SpectralCorrelator(const SpectralCorrelator&) = delete;
SpectralCorrelator& operator=(const SpectralCorrelator&) = delete;
~SpectralCorrelator();
// Computes the band-wise spectral auto-correlations.
// `x` must:
// - have size equal to `kFrameSize20ms24kHz`;
// - be encoded as vectors of interleaved real-complex FFT coefficients
// where x[1] = y[1] = 0 (the Nyquist frequency coefficient is omitted).
void ComputeAutoCorrelation(
rtc::ArrayView<const float> x,
rtc::ArrayView<float, kOpusBands24kHz> auto_corr) const;
// Computes the band-wise spectral cross-correlations.
// `x` and `y` must:
// - have size equal to `kFrameSize20ms24kHz`;
// - be encoded as vectors of interleaved real-complex FFT coefficients where
// x[1] = y[1] = 0 (the Nyquist frequency coefficient is omitted).
void ComputeCrossCorrelation(
rtc::ArrayView<const float> x,
rtc::ArrayView<const float> y,
rtc::ArrayView<float, kOpusBands24kHz> cross_corr) const;
private:
const std::vector<float> weights_; // Weights for each Fourier coefficient.
};
// TODO(bugs.webrtc.org/10480): Move to anonymous namespace in
// spectral_features.cc. Given a vector of Opus-bands energy coefficients,
// computes the log magnitude spectrum applying smoothing both over time and
// over frequency. Declared here for unit testing.
void ComputeSmoothedLogMagnitudeSpectrum(
rtc::ArrayView<const float> bands_energy,
rtc::ArrayView<float, kNumBands> log_bands_energy);
// TODO(bugs.webrtc.org/10480): Move to anonymous namespace in
// spectral_features.cc. Creates a DCT table for arrays having size equal to
// `kNumBands`. Declared here for unit testing.
std::array<float, kNumBands * kNumBands> ComputeDctTable();
// TODO(bugs.webrtc.org/10480): Move to anonymous namespace in
// spectral_features.cc. Computes DCT for `in` given a pre-computed DCT table.
// In-place computation is not allowed and `out` can be smaller than `in` in
// order to only compute the first DCT coefficients. Declared here for unit
// testing.
void ComputeDct(rtc::ArrayView<const float> in,
rtc::ArrayView<const float, kNumBands * kNumBands> dct_table,
rtc::ArrayView<float> out);
} // namespace rnn_vad
} // namespace webrtc
#endif // MODULES_AUDIO_PROCESSING_AGC2_RNN_VAD_SPECTRAL_FEATURES_INTERNAL_H_