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/high_pass_filter_impl.h"
12
13#include "webrtc/common_audio/signal_processing/include/signal_processing_library.h"
14#include "webrtc/modules/audio_processing/audio_buffer.h"
15#include "webrtc/system_wrappers/include/critical_section_wrapper.h"
16
17namespace webrtc {
18namespace {
19const int16_t kFilterCoefficients8kHz[5] = {3798, -7596, 3798, 7807, -3733};
20const int16_t kFilterCoefficients[5] = {4012, -8024, 4012, 8002, -3913};
21}  // namespace
22
23class HighPassFilterImpl::BiquadFilter {
24 public:
25  explicit BiquadFilter(int sample_rate_hz) :
26      ba_(sample_rate_hz == AudioProcessing::kSampleRate8kHz ?
27          kFilterCoefficients8kHz : kFilterCoefficients)
28  {
29    Reset();
30  }
31
32  void Reset() {
33    std::memset(x_, 0, sizeof(x_));
34    std::memset(y_, 0, sizeof(y_));
35  }
36
37  void Process(int16_t* data, size_t length) {
38    const int16_t* const ba = ba_;
39    int16_t* x = x_;
40    int16_t* y = y_;
41    int32_t tmp_int32 = 0;
42
43    for (size_t i = 0; i < length; i++) {
44      //  y[i] = b[0] * x[i] +  b[1] * x[i-1] +  b[2] * x[i-2]
45      //                     + -a[1] * y[i-1] + -a[2] * y[i-2];
46
47      tmp_int32 = y[1] * ba[3];      // -a[1] * y[i-1] (low part)
48      tmp_int32 += y[3] * ba[4];     // -a[2] * y[i-2] (low part)
49      tmp_int32 = (tmp_int32 >> 15);
50      tmp_int32 += y[0] * ba[3];     // -a[1] * y[i-1] (high part)
51      tmp_int32 += y[2] * ba[4];     // -a[2] * y[i-2] (high part)
52      tmp_int32 = (tmp_int32 << 1);
53
54      tmp_int32 += data[i] * ba[0];  // b[0] * x[0]
55      tmp_int32 += x[0] * ba[1];     // b[1] * x[i-1]
56      tmp_int32 += x[1] * ba[2];     // b[2] * x[i-2]
57
58      // Update state (input part).
59      x[1] = x[0];
60      x[0] = data[i];
61
62      // Update state (filtered part).
63      y[2] = y[0];
64      y[3] = y[1];
65      y[0] = static_cast<int16_t>(tmp_int32 >> 13);
66      y[1] = static_cast<int16_t>(
67          (tmp_int32 - (static_cast<int32_t>(y[0]) << 13)) << 2);
68
69      // Rounding in Q12, i.e. add 2^11.
70      tmp_int32 += 2048;
71
72      // Saturate (to 2^27) so that the HP filtered signal does not overflow.
73      tmp_int32 = WEBRTC_SPL_SAT(static_cast<int32_t>(134217727),
74                                 tmp_int32,
75                                 static_cast<int32_t>(-134217728));
76
77      // Convert back to Q0 and use rounding.
78      data[i] = static_cast<int16_t>(tmp_int32 >> 12);
79    }
80  }
81
82 private:
83  const int16_t* const ba_ = nullptr;
84  int16_t x_[2];
85  int16_t y_[4];
86};
87
88HighPassFilterImpl::HighPassFilterImpl(rtc::CriticalSection* crit)
89    : crit_(crit) {
90  RTC_DCHECK(crit_);
91}
92
93HighPassFilterImpl::~HighPassFilterImpl() {}
94
95void HighPassFilterImpl::Initialize(size_t channels, int sample_rate_hz) {
96  std::vector<rtc::scoped_ptr<BiquadFilter>> new_filters(channels);
97  for (size_t i = 0; i < channels; i++) {
98    new_filters[i].reset(new BiquadFilter(sample_rate_hz));
99  }
100  rtc::CritScope cs(crit_);
101  filters_.swap(new_filters);
102}
103
104void HighPassFilterImpl::ProcessCaptureAudio(AudioBuffer* audio) {
105  RTC_DCHECK(audio);
106  rtc::CritScope cs(crit_);
107  if (!enabled_) {
108    return;
109  }
110
111  RTC_DCHECK_GE(160u, audio->num_frames_per_band());
112  RTC_DCHECK_EQ(filters_.size(), audio->num_channels());
113  for (size_t i = 0; i < filters_.size(); i++) {
114    filters_[i]->Process(audio->split_bands(i)[kBand0To8kHz],
115                         audio->num_frames_per_band());
116  }
117}
118
119int HighPassFilterImpl::Enable(bool enable) {
120  rtc::CritScope cs(crit_);
121  if (!enabled_ && enable) {
122    for (auto& filter : filters_) {
123      filter->Reset();
124    }
125  }
126  enabled_ = enable;
127  return AudioProcessing::kNoError;
128}
129
130bool HighPassFilterImpl::is_enabled() const {
131  rtc::CritScope cs(crit_);
132  return enabled_;
133}
134}  // namespace webrtc
135