1/*
2 *  Copyright (c) 2013 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// MSVC++ requires this to be set before any other includes to get M_PI.
12#define _USE_MATH_DEFINES
13
14#include "webrtc/common_audio/resampler/sinusoidal_linear_chirp_source.h"
15
16#include <math.h>
17
18namespace webrtc {
19
20SinusoidalLinearChirpSource::SinusoidalLinearChirpSource(int sample_rate,
21  int samples, double max_frequency, double delay_samples)
22    : sample_rate_(sample_rate),
23      total_samples_(samples),
24      max_frequency_(max_frequency),
25      current_index_(0),
26      delay_samples_(delay_samples) {
27  // Chirp rate.
28  double duration = static_cast<double>(total_samples_) / sample_rate_;
29  k_ = (max_frequency_ - kMinFrequency) / duration;
30}
31
32void SinusoidalLinearChirpSource::Run(int frames, float* destination) {
33  for (int i = 0; i < frames; ++i, ++current_index_) {
34    // Filter out frequencies higher than Nyquist.
35    if (Frequency(current_index_) > 0.5 * sample_rate_) {
36      destination[i] = 0;
37    } else {
38      // Calculate time in seconds.
39      double t = (static_cast<double>(current_index_) - delay_samples_) /
40          sample_rate_;
41      if (t < 0) {
42        destination[i] = 0;
43      } else {
44        // Sinusoidal linear chirp.
45        destination[i] =
46            sin(2 * M_PI * (kMinFrequency * t + (k_ / 2) * t * t));
47      }
48    }
49  }
50}
51
52double SinusoidalLinearChirpSource::Frequency(int position) {
53  return kMinFrequency + (position - delay_samples_) *
54      (max_frequency_ - kMinFrequency) / total_samples_;
55}
56
57}  // namespace webrtc
58