1 /* 2 * Copyright (c) 2012 The WebRTC project authors. All Rights Reserved. 3 * 4 * Use of this source code is governed by a BSD-style license 5 * that can be found in the LICENSE file in the root of the source 6 * tree. An additional intellectual property rights grant can be found 7 * in the file PATENTS. All contributing project authors may 8 * be found in the AUTHORS file in the root of the source tree. 9 */ 10 11 #include "webrtc/modules/audio_processing/vad/pitch_internal.h" 12 13 #include <cmath> 14 15 // A 4-to-3 linear interpolation. 16 // The interpolation constants are derived as following: 17 // Input pitch parameters are updated every 7.5 ms. Within a 30-ms interval 18 // we are interested in pitch parameters of 0-5 ms, 10-15ms and 20-25ms. This is 19 // like interpolating 4-to-6 and keep the odd samples. 20 // The reason behind this is that LPC coefficients are computed for the first 21 // half of each 10ms interval. 22 static void PitchInterpolation(double old_val, const double* in, double* out) { 23 out[0] = 1. / 6. * old_val + 5. / 6. * in[0]; 24 out[1] = 5. / 6. * in[1] + 1. / 6. * in[2]; 25 out[2] = 0.5 * in[2] + 0.5 * in[3]; 26 } 27 28 void GetSubframesPitchParameters(int sampling_rate_hz, 29 double* gains, 30 double* lags, 31 int num_in_frames, 32 int num_out_frames, 33 double* log_old_gain, 34 double* old_lag, 35 double* log_pitch_gain, 36 double* pitch_lag_hz) { 37 // Gain interpolation is in log-domain, also returned in log-domain. 38 for (int n = 0; n < num_in_frames; n++) 39 gains[n] = log(gains[n] + 1e-12); 40 41 // Interpolate lags and gains. 42 PitchInterpolation(*log_old_gain, gains, log_pitch_gain); 43 *log_old_gain = gains[num_in_frames - 1]; 44 PitchInterpolation(*old_lag, lags, pitch_lag_hz); 45 *old_lag = lags[num_in_frames - 1]; 46 47 // Convert pitch-lags to Hertz. 48 for (int n = 0; n < num_out_frames; n++) { 49 pitch_lag_hz[n] = (sampling_rate_hz) / (pitch_lag_hz[n]); 50 } 51 } 52
