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/*
* Copyright (c) 2012 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/vad/pitch_internal.h"
#include <cmath>
namespace webrtc {
// A 4-to-3 linear interpolation.
// The interpolation constants are derived as following:
// Input pitch parameters are updated every 7.5 ms. Within a 30-ms interval
// we are interested in pitch parameters of 0-5 ms, 10-15ms and 20-25ms. This is
// like interpolating 4-to-6 and keep the odd samples.
// The reason behind this is that LPC coefficients are computed for the first
// half of each 10ms interval.
static void PitchInterpolation(double old_val, const double* in, double* out) {
out[0] = 1. / 6. * old_val + 5. / 6. * in[0];
out[1] = 5. / 6. * in[1] + 1. / 6. * in[2];
out[2] = 0.5 * in[2] + 0.5 * in[3];
}
void GetSubframesPitchParameters(int sampling_rate_hz,
double* gains,
double* lags,
int num_in_frames,
int num_out_frames,
double* log_old_gain,
double* old_lag,
double* log_pitch_gain,
double* pitch_lag_hz) {
// Gain interpolation is in log-domain, also returned in log-domain.
for (int n = 0; n < num_in_frames; n++)
gains[n] = log(gains[n] + 1e-12);
// Interpolate lags and gains.
PitchInterpolation(*log_old_gain, gains, log_pitch_gain);
*log_old_gain = gains[num_in_frames - 1];
PitchInterpolation(*old_lag, lags, pitch_lag_hz);
*old_lag = lags[num_in_frames - 1];
// Convert pitch-lags to Hertz.
for (int n = 0; n < num_out_frames; n++) {
pitch_lag_hz[n] = (sampling_rate_hz) / (pitch_lag_hz[n]);
}
}
} // namespace webrtc
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