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_coding/neteq/time_stretch.h"
12
13 #include <algorithm> // min, max
14
15 #include "webrtc/base/safe_conversions.h"
16 #include "webrtc/base/scoped_ptr.h"
17 #include "webrtc/common_audio/signal_processing/include/signal_processing_library.h"
18 #include "webrtc/modules/audio_coding/neteq/background_noise.h"
19 #include "webrtc/modules/audio_coding/neteq/dsp_helper.h"
20
21 namespace webrtc {
22
Process(const int16_t * input,size_t input_len,bool fast_mode,AudioMultiVector * output,size_t * length_change_samples)23 TimeStretch::ReturnCodes TimeStretch::Process(const int16_t* input,
24 size_t input_len,
25 bool fast_mode,
26 AudioMultiVector* output,
27 size_t* length_change_samples) {
28 // Pre-calculate common multiplication with |fs_mult_|.
29 size_t fs_mult_120 =
30 static_cast<size_t>(fs_mult_ * 120); // Corresponds to 15 ms.
31
32 const int16_t* signal;
33 rtc::scoped_ptr<int16_t[]> signal_array;
34 size_t signal_len;
35 if (num_channels_ == 1) {
36 signal = input;
37 signal_len = input_len;
38 } else {
39 // We want |signal| to be only the first channel of |input|, which is
40 // interleaved. Thus, we take the first sample, skip forward |num_channels|
41 // samples, and continue like that.
42 signal_len = input_len / num_channels_;
43 signal_array.reset(new int16_t[signal_len]);
44 signal = signal_array.get();
45 size_t j = master_channel_;
46 for (size_t i = 0; i < signal_len; ++i) {
47 signal_array[i] = input[j];
48 j += num_channels_;
49 }
50 }
51
52 // Find maximum absolute value of input signal.
53 max_input_value_ = WebRtcSpl_MaxAbsValueW16(signal, signal_len);
54
55 // Downsample to 4 kHz sample rate and calculate auto-correlation.
56 DspHelper::DownsampleTo4kHz(signal, signal_len, kDownsampledLen,
57 sample_rate_hz_, true /* compensate delay*/,
58 downsampled_input_);
59 AutoCorrelation();
60
61 // Find the strongest correlation peak.
62 static const size_t kNumPeaks = 1;
63 size_t peak_index;
64 int16_t peak_value;
65 DspHelper::PeakDetection(auto_correlation_, kCorrelationLen, kNumPeaks,
66 fs_mult_, &peak_index, &peak_value);
67 // Assert that |peak_index| stays within boundaries.
68 assert(peak_index <= (2 * kCorrelationLen - 1) * fs_mult_);
69
70 // Compensate peak_index for displaced starting position. The displacement
71 // happens in AutoCorrelation(). Here, |kMinLag| is in the down-sampled 4 kHz
72 // domain, while the |peak_index| is in the original sample rate; hence, the
73 // multiplication by fs_mult_ * 2.
74 peak_index += kMinLag * fs_mult_ * 2;
75 // Assert that |peak_index| stays within boundaries.
76 assert(peak_index >= static_cast<size_t>(20 * fs_mult_));
77 assert(peak_index <= 20 * fs_mult_ + (2 * kCorrelationLen - 1) * fs_mult_);
78
79 // Calculate scaling to ensure that |peak_index| samples can be square-summed
80 // without overflowing.
81 int scaling = 31 - WebRtcSpl_NormW32(max_input_value_ * max_input_value_) -
82 WebRtcSpl_NormW32(static_cast<int32_t>(peak_index));
83 scaling = std::max(0, scaling);
84
85 // |vec1| starts at 15 ms minus one pitch period.
86 const int16_t* vec1 = &signal[fs_mult_120 - peak_index];
87 // |vec2| start at 15 ms.
88 const int16_t* vec2 = &signal[fs_mult_120];
89 // Calculate energies for |vec1| and |vec2|, assuming they both contain
90 // |peak_index| samples.
91 int32_t vec1_energy =
92 WebRtcSpl_DotProductWithScale(vec1, vec1, peak_index, scaling);
93 int32_t vec2_energy =
94 WebRtcSpl_DotProductWithScale(vec2, vec2, peak_index, scaling);
95
96 // Calculate cross-correlation between |vec1| and |vec2|.
97 int32_t cross_corr =
98 WebRtcSpl_DotProductWithScale(vec1, vec2, peak_index, scaling);
99
100 // Check if the signal seems to be active speech or not (simple VAD).
101 bool active_speech = SpeechDetection(vec1_energy, vec2_energy, peak_index,
102 scaling);
103
104 int16_t best_correlation;
105 if (!active_speech) {
106 SetParametersForPassiveSpeech(signal_len, &best_correlation, &peak_index);
107 } else {
108 // Calculate correlation:
109 // cross_corr / sqrt(vec1_energy * vec2_energy).
110
111 // Start with calculating scale values.
112 int energy1_scale = std::max(0, 16 - WebRtcSpl_NormW32(vec1_energy));
113 int energy2_scale = std::max(0, 16 - WebRtcSpl_NormW32(vec2_energy));
114
115 // Make sure total scaling is even (to simplify scale factor after sqrt).
116 if ((energy1_scale + energy2_scale) & 1) {
117 // The sum is odd.
118 energy1_scale += 1;
119 }
120
121 // Scale energies to int16_t.
122 int16_t vec1_energy_int16 =
123 static_cast<int16_t>(vec1_energy >> energy1_scale);
124 int16_t vec2_energy_int16 =
125 static_cast<int16_t>(vec2_energy >> energy2_scale);
126
127 // Calculate square-root of energy product.
128 int16_t sqrt_energy_prod = WebRtcSpl_SqrtFloor(vec1_energy_int16 *
129 vec2_energy_int16);
130
131 // Calculate cross_corr / sqrt(en1*en2) in Q14.
132 int temp_scale = 14 - (energy1_scale + energy2_scale) / 2;
133 cross_corr = WEBRTC_SPL_SHIFT_W32(cross_corr, temp_scale);
134 cross_corr = std::max(0, cross_corr); // Don't use if negative.
135 best_correlation = WebRtcSpl_DivW32W16(cross_corr, sqrt_energy_prod);
136 // Make sure |best_correlation| is no larger than 1 in Q14.
137 best_correlation = std::min(static_cast<int16_t>(16384), best_correlation);
138 }
139
140
141 // Check accelerate criteria and stretch the signal.
142 ReturnCodes return_value =
143 CheckCriteriaAndStretch(input, input_len, peak_index, best_correlation,
144 active_speech, fast_mode, output);
145 switch (return_value) {
146 case kSuccess:
147 *length_change_samples = peak_index;
148 break;
149 case kSuccessLowEnergy:
150 *length_change_samples = peak_index;
151 break;
152 case kNoStretch:
153 case kError:
154 *length_change_samples = 0;
155 break;
156 }
157 return return_value;
158 }
159
AutoCorrelation()160 void TimeStretch::AutoCorrelation() {
161 // Set scaling factor for cross correlation to protect against overflow.
162 int scaling = kLogCorrelationLen - WebRtcSpl_NormW32(
163 max_input_value_ * max_input_value_);
164 scaling = std::max(0, scaling);
165
166 // Calculate correlation from lag kMinLag to lag kMaxLag in 4 kHz domain.
167 int32_t auto_corr[kCorrelationLen];
168 WebRtcSpl_CrossCorrelation(auto_corr, &downsampled_input_[kMaxLag],
169 &downsampled_input_[kMaxLag - kMinLag],
170 kCorrelationLen, kMaxLag - kMinLag, scaling, -1);
171
172 // Normalize correlation to 14 bits and write to |auto_correlation_|.
173 int32_t max_corr = WebRtcSpl_MaxAbsValueW32(auto_corr, kCorrelationLen);
174 scaling = std::max(0, 17 - WebRtcSpl_NormW32(max_corr));
175 WebRtcSpl_VectorBitShiftW32ToW16(auto_correlation_, kCorrelationLen,
176 auto_corr, scaling);
177 }
178
SpeechDetection(int32_t vec1_energy,int32_t vec2_energy,size_t peak_index,int scaling) const179 bool TimeStretch::SpeechDetection(int32_t vec1_energy, int32_t vec2_energy,
180 size_t peak_index, int scaling) const {
181 // Check if the signal seems to be active speech or not (simple VAD).
182 // If (vec1_energy + vec2_energy) / (2 * peak_index) <=
183 // 8 * background_noise_energy, then we say that the signal contains no
184 // active speech.
185 // Rewrite the inequality as:
186 // (vec1_energy + vec2_energy) / 16 <= peak_index * background_noise_energy.
187 // The two sides of the inequality will be denoted |left_side| and
188 // |right_side|.
189 int32_t left_side = (vec1_energy + vec2_energy) / 16;
190 int32_t right_side;
191 if (background_noise_.initialized()) {
192 right_side = background_noise_.Energy(master_channel_);
193 } else {
194 // If noise parameters have not been estimated, use a fixed threshold.
195 right_side = 75000;
196 }
197 int right_scale = 16 - WebRtcSpl_NormW32(right_side);
198 right_scale = std::max(0, right_scale);
199 left_side = left_side >> right_scale;
200 right_side =
201 rtc::checked_cast<int32_t>(peak_index) * (right_side >> right_scale);
202
203 // Scale |left_side| properly before comparing with |right_side|.
204 // (|scaling| is the scale factor before energy calculation, thus the scale
205 // factor for the energy is 2 * scaling.)
206 if (WebRtcSpl_NormW32(left_side) < 2 * scaling) {
207 // Cannot scale only |left_side|, must scale |right_side| too.
208 int temp_scale = WebRtcSpl_NormW32(left_side);
209 left_side = left_side << temp_scale;
210 right_side = right_side >> (2 * scaling - temp_scale);
211 } else {
212 left_side = left_side << 2 * scaling;
213 }
214 return left_side > right_side;
215 }
216
217 } // namespace webrtc
218