52 lines
2.1 KiB
C++
52 lines
2.1 KiB
C++
/*
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* Copyright (c) 2012 The WebRTC project authors. All Rights Reserved.
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*
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* Use of this source code is governed by a BSD-style license
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* that can be found in the LICENSE file in the root of the source
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* tree. An additional intellectual property rights grant can be found
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* in the file PATENTS. All contributing project authors may
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* be found in the AUTHORS file in the root of the source tree.
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*/
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#include "modules/audio_processing/vad/pitch_internal.h"
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#include <cmath>
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// A 4-to-3 linear interpolation.
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// The interpolation constants are derived as following:
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// Input pitch parameters are updated every 7.5 ms. Within a 30-ms interval
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// we are interested in pitch parameters of 0-5 ms, 10-15ms and 20-25ms. This is
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// like interpolating 4-to-6 and keep the odd samples.
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// The reason behind this is that LPC coefficients are computed for the first
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// half of each 10ms interval.
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static void PitchInterpolation(double old_val, const double* in, double* out) {
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out[0] = 1. / 6. * old_val + 5. / 6. * in[0];
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out[1] = 5. / 6. * in[1] + 1. / 6. * in[2];
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out[2] = 0.5 * in[2] + 0.5 * in[3];
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}
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void GetSubframesPitchParameters(int sampling_rate_hz,
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double* gains,
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double* lags,
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int num_in_frames,
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int num_out_frames,
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double* log_old_gain,
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double* old_lag,
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double* log_pitch_gain,
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double* pitch_lag_hz) {
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// Gain interpolation is in log-domain, also returned in log-domain.
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for (int n = 0; n < num_in_frames; n++)
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gains[n] = log(gains[n] + 1e-12);
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// Interpolate lags and gains.
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PitchInterpolation(*log_old_gain, gains, log_pitch_gain);
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*log_old_gain = gains[num_in_frames - 1];
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PitchInterpolation(*old_lag, lags, pitch_lag_hz);
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*old_lag = lags[num_in_frames - 1];
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// Convert pitch-lags to Hertz.
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for (int n = 0; n < num_out_frames; n++) {
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pitch_lag_hz[n] = (sampling_rate_hz) / (pitch_lag_hz[n]);
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}
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}
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