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 "modules/audio_coding/neteq/time_stretch.h"
12
13 #include <algorithm> // min, max
14 #include <memory>
15
16 #include "common_audio/signal_processing/include/signal_processing_library.h"
17 #include "modules/audio_coding/neteq/background_noise.h"
18 #include "modules/audio_coding/neteq/cross_correlation.h"
19 #include "modules/audio_coding/neteq/dsp_helper.h"
20 #include "rtc_base/numerics/safe_conversions.h"
21
22 namespace webrtc {
23
Process(const int16_t * input,size_t input_len,bool fast_mode,AudioMultiVector * output,size_t * length_change_samples)24 TimeStretch::ReturnCodes TimeStretch::Process(const int16_t* input,
25 size_t input_len,
26 bool fast_mode,
27 AudioMultiVector* output,
28 size_t* length_change_samples) {
29 // Pre-calculate common multiplication with |fs_mult_|.
30 size_t fs_mult_120 =
31 static_cast<size_t>(fs_mult_ * 120); // Corresponds to 15 ms.
32
33 const int16_t* signal;
34 std::unique_ptr<int16_t[]> signal_array;
35 size_t signal_len;
36 if (num_channels_ == 1) {
37 signal = input;
38 signal_len = input_len;
39 } else {
40 // We want |signal| to be only the first channel of |input|, which is
41 // interleaved. Thus, we take the first sample, skip forward |num_channels|
42 // samples, and continue like that.
43 signal_len = input_len / num_channels_;
44 signal_array.reset(new int16_t[signal_len]);
45 signal = signal_array.get();
46 size_t j = kRefChannel;
47 for (size_t i = 0; i < signal_len; ++i) {
48 signal_array[i] = input[j];
49 j += num_channels_;
50 }
51 }
52
53 // Find maximum absolute value of input signal.
54 max_input_value_ = WebRtcSpl_MaxAbsValueW16(signal, signal_len);
55
56 // Downsample to 4 kHz sample rate and calculate auto-correlation.
57 DspHelper::DownsampleTo4kHz(signal, signal_len, kDownsampledLen,
58 sample_rate_hz_, true /* compensate delay*/,
59 downsampled_input_);
60 AutoCorrelation();
61
62 // Find the strongest correlation peak.
63 static const size_t kNumPeaks = 1;
64 size_t peak_index;
65 int16_t peak_value;
66 DspHelper::PeakDetection(auto_correlation_, kCorrelationLen, kNumPeaks,
67 fs_mult_, &peak_index, &peak_value);
68 // Assert that |peak_index| stays within boundaries.
69 assert(peak_index <= (2 * kCorrelationLen - 1) * fs_mult_);
70
71 // Compensate peak_index for displaced starting position. The displacement
72 // happens in AutoCorrelation(). Here, |kMinLag| is in the down-sampled 4 kHz
73 // domain, while the |peak_index| is in the original sample rate; hence, the
74 // multiplication by fs_mult_ * 2.
75 peak_index += kMinLag * fs_mult_ * 2;
76 // Assert that |peak_index| stays within boundaries.
77 assert(peak_index >= static_cast<size_t>(20 * fs_mult_));
78 assert(peak_index <= 20 * fs_mult_ + (2 * kCorrelationLen - 1) * fs_mult_);
79
80 // Calculate scaling to ensure that |peak_index| samples can be square-summed
81 // without overflowing.
82 int scaling = 31 - WebRtcSpl_NormW32(max_input_value_ * max_input_value_) -
83 WebRtcSpl_NormW32(static_cast<int32_t>(peak_index));
84 scaling = std::max(0, scaling);
85
86 // |vec1| starts at 15 ms minus one pitch period.
87 const int16_t* vec1 = &signal[fs_mult_120 - peak_index];
88 // |vec2| start at 15 ms.
89 const int16_t* vec2 = &signal[fs_mult_120];
90 // Calculate energies for |vec1| and |vec2|, assuming they both contain
91 // |peak_index| samples.
92 int32_t vec1_energy =
93 WebRtcSpl_DotProductWithScale(vec1, vec1, peak_index, scaling);
94 int32_t vec2_energy =
95 WebRtcSpl_DotProductWithScale(vec2, vec2, peak_index, scaling);
96
97 // Calculate cross-correlation between |vec1| and |vec2|.
98 int32_t cross_corr =
99 WebRtcSpl_DotProductWithScale(vec1, vec2, peak_index, scaling);
100
101 // Check if the signal seems to be active speech or not (simple VAD).
102 bool active_speech =
103 SpeechDetection(vec1_energy, vec2_energy, peak_index, scaling);
104
105 int16_t best_correlation;
106 if (!active_speech) {
107 SetParametersForPassiveSpeech(signal_len, &best_correlation, &peak_index);
108 } else {
109 // Calculate correlation:
110 // cross_corr / sqrt(vec1_energy * vec2_energy).
111
112 // Start with calculating scale values.
113 int energy1_scale = std::max(0, 16 - WebRtcSpl_NormW32(vec1_energy));
114 int energy2_scale = std::max(0, 16 - WebRtcSpl_NormW32(vec2_energy));
115
116 // Make sure total scaling is even (to simplify scale factor after sqrt).
117 if ((energy1_scale + energy2_scale) & 1) {
118 // The sum is odd.
119 energy1_scale += 1;
120 }
121
122 // Scale energies to int16_t.
123 int16_t vec1_energy_int16 =
124 static_cast<int16_t>(vec1_energy >> energy1_scale);
125 int16_t vec2_energy_int16 =
126 static_cast<int16_t>(vec2_energy >> energy2_scale);
127
128 // Calculate square-root of energy product.
129 int16_t sqrt_energy_prod =
130 WebRtcSpl_SqrtFloor(vec1_energy_int16 * vec2_energy_int16);
131
132 // Calculate cross_corr / sqrt(en1*en2) in Q14.
133 int temp_scale = 14 - (energy1_scale + energy2_scale) / 2;
134 cross_corr = WEBRTC_SPL_SHIFT_W32(cross_corr, temp_scale);
135 cross_corr = std::max(0, cross_corr); // Don't use if negative.
136 best_correlation = WebRtcSpl_DivW32W16(cross_corr, sqrt_energy_prod);
137 // Make sure |best_correlation| is no larger than 1 in Q14.
138 best_correlation = std::min(static_cast<int16_t>(16384), best_correlation);
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 // Calculate correlation from lag kMinLag to lag kMaxLag in 4 kHz domain.
162 int32_t auto_corr[kCorrelationLen];
163 CrossCorrelationWithAutoShift(
164 &downsampled_input_[kMaxLag], &downsampled_input_[kMaxLag - kMinLag],
165 kCorrelationLen, kMaxLag - kMinLag, -1, auto_corr);
166
167 // Normalize correlation to 14 bits and write to |auto_correlation_|.
168 int32_t max_corr = WebRtcSpl_MaxAbsValueW32(auto_corr, kCorrelationLen);
169 int scaling = std::max(0, 17 - WebRtcSpl_NormW32(max_corr));
170 WebRtcSpl_VectorBitShiftW32ToW16(auto_correlation_, kCorrelationLen,
171 auto_corr, scaling);
172 }
173
SpeechDetection(int32_t vec1_energy,int32_t vec2_energy,size_t peak_index,int scaling) const174 bool TimeStretch::SpeechDetection(int32_t vec1_energy,
175 int32_t vec2_energy,
176 size_t peak_index,
177 int scaling) const {
178 // Check if the signal seems to be active speech or not (simple VAD).
179 // If (vec1_energy + vec2_energy) / (2 * peak_index) <=
180 // 8 * background_noise_energy, then we say that the signal contains no
181 // active speech.
182 // Rewrite the inequality as:
183 // (vec1_energy + vec2_energy) / 16 <= peak_index * background_noise_energy.
184 // The two sides of the inequality will be denoted |left_side| and
185 // |right_side|.
186 int32_t left_side = rtc::saturated_cast<int32_t>(
187 (static_cast<int64_t>(vec1_energy) + vec2_energy) / 16);
188 int32_t right_side;
189 if (background_noise_.initialized()) {
190 right_side = background_noise_.Energy(kRefChannel);
191 } else {
192 // If noise parameters have not been estimated, use a fixed threshold.
193 right_side = 75000;
194 }
195 int right_scale = 16 - WebRtcSpl_NormW32(right_side);
196 right_scale = std::max(0, right_scale);
197 left_side = left_side >> right_scale;
198 right_side =
199 rtc::dchecked_cast<int32_t>(peak_index) * (right_side >> right_scale);
200
201 // Scale |left_side| properly before comparing with |right_side|.
202 // (|scaling| is the scale factor before energy calculation, thus the scale
203 // factor for the energy is 2 * scaling.)
204 if (WebRtcSpl_NormW32(left_side) < 2 * scaling) {
205 // Cannot scale only |left_side|, must scale |right_side| too.
206 int temp_scale = WebRtcSpl_NormW32(left_side);
207 left_side = left_side << temp_scale;
208 right_side = right_side >> (2 * scaling - temp_scale);
209 } else {
210 left_side = left_side << 2 * scaling;
211 }
212 return left_side > right_side;
213 }
214
215 } // namespace webrtc
216