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
17 namespace webrtc {
18 namespace {
19 const int16_t kFilterCoefficients8kHz[5] = {3798, -7596, 3798, 7807, -3733};
20 const int16_t kFilterCoefficients[5] = {4012, -8024, 4012, 8002, -3913};
21 } // namespace
22
23 class HighPassFilterImpl::BiquadFilter {
24 public:
BiquadFilter(int sample_rate_hz)25 explicit BiquadFilter(int sample_rate_hz) :
26 ba_(sample_rate_hz == AudioProcessing::kSampleRate8kHz ?
27 kFilterCoefficients8kHz : kFilterCoefficients)
28 {
29 Reset();
30 }
31
Reset()32 void Reset() {
33 std::memset(x_, 0, sizeof(x_));
34 std::memset(y_, 0, sizeof(y_));
35 }
36
Process(int16_t * data,size_t length)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
HighPassFilterImpl(rtc::CriticalSection * crit)88 HighPassFilterImpl::HighPassFilterImpl(rtc::CriticalSection* crit)
89 : crit_(crit) {
90 RTC_DCHECK(crit_);
91 }
92
~HighPassFilterImpl()93 HighPassFilterImpl::~HighPassFilterImpl() {}
94
Initialize(size_t channels,int sample_rate_hz)95 void 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
ProcessCaptureAudio(AudioBuffer * audio)104 void 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
Enable(bool enable)119 int 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
is_enabled() const130 bool HighPassFilterImpl::is_enabled() const {
131 rtc::CritScope cs(crit_);
132 return enabled_;
133 }
134 } // namespace webrtc
135