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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 /* Resamples a signal to an arbitrary rate. Used by the AEC to compensate for
12  * clock skew by resampling the farend signal.
13  */
14 
15 #include "webrtc/modules/audio_processing/aec/aec_resampler.h"
16 
17 #include <assert.h>
18 #include <math.h>
19 #include <stdlib.h>
20 #include <string.h>
21 
22 #include "webrtc/modules/audio_processing/aec/aec_core.h"
23 
24 enum {
25   kEstimateLengthFrames = 400
26 };
27 
28 typedef struct {
29   float buffer[kResamplerBufferSize];
30   float position;
31 
32   int deviceSampleRateHz;
33   int skewData[kEstimateLengthFrames];
34   int skewDataIndex;
35   float skewEstimate;
36 } AecResampler;
37 
38 static int EstimateSkew(const int* rawSkew,
39                         int size,
40                         int absLimit,
41                         float* skewEst);
42 
WebRtcAec_CreateResampler()43 void* WebRtcAec_CreateResampler() {
44   return malloc(sizeof(AecResampler));
45 }
46 
WebRtcAec_InitResampler(void * resampInst,int deviceSampleRateHz)47 int WebRtcAec_InitResampler(void* resampInst, int deviceSampleRateHz) {
48   AecResampler* obj = (AecResampler*)resampInst;
49   memset(obj->buffer, 0, sizeof(obj->buffer));
50   obj->position = 0.0;
51 
52   obj->deviceSampleRateHz = deviceSampleRateHz;
53   memset(obj->skewData, 0, sizeof(obj->skewData));
54   obj->skewDataIndex = 0;
55   obj->skewEstimate = 0.0;
56 
57   return 0;
58 }
59 
WebRtcAec_FreeResampler(void * resampInst)60 void WebRtcAec_FreeResampler(void* resampInst) {
61   AecResampler* obj = (AecResampler*)resampInst;
62   free(obj);
63 }
64 
WebRtcAec_ResampleLinear(void * resampInst,const float * inspeech,size_t size,float skew,float * outspeech,size_t * size_out)65 void WebRtcAec_ResampleLinear(void* resampInst,
66                               const float* inspeech,
67                               size_t size,
68                               float skew,
69                               float* outspeech,
70                               size_t* size_out) {
71   AecResampler* obj = (AecResampler*)resampInst;
72 
73   float* y;
74   float be, tnew;
75   size_t tn, mm;
76 
77   assert(size <= 2 * FRAME_LEN);
78   assert(resampInst != NULL);
79   assert(inspeech != NULL);
80   assert(outspeech != NULL);
81   assert(size_out != NULL);
82 
83   // Add new frame data in lookahead
84   memcpy(&obj->buffer[FRAME_LEN + kResamplingDelay],
85          inspeech,
86          size * sizeof(inspeech[0]));
87 
88   // Sample rate ratio
89   be = 1 + skew;
90 
91   // Loop over input frame
92   mm = 0;
93   y = &obj->buffer[FRAME_LEN];  // Point at current frame
94 
95   tnew = be * mm + obj->position;
96   tn = (size_t)tnew;
97 
98   while (tn < size) {
99 
100     // Interpolation
101     outspeech[mm] = y[tn] + (tnew - tn) * (y[tn + 1] - y[tn]);
102     mm++;
103 
104     tnew = be * mm + obj->position;
105     tn = (int)tnew;
106   }
107 
108   *size_out = mm;
109   obj->position += (*size_out) * be - size;
110 
111   // Shift buffer
112   memmove(obj->buffer,
113           &obj->buffer[size],
114           (kResamplerBufferSize - size) * sizeof(obj->buffer[0]));
115 }
116 
WebRtcAec_GetSkew(void * resampInst,int rawSkew,float * skewEst)117 int WebRtcAec_GetSkew(void* resampInst, int rawSkew, float* skewEst) {
118   AecResampler* obj = (AecResampler*)resampInst;
119   int err = 0;
120 
121   if (obj->skewDataIndex < kEstimateLengthFrames) {
122     obj->skewData[obj->skewDataIndex] = rawSkew;
123     obj->skewDataIndex++;
124   } else if (obj->skewDataIndex == kEstimateLengthFrames) {
125     err = EstimateSkew(
126         obj->skewData, kEstimateLengthFrames, obj->deviceSampleRateHz, skewEst);
127     obj->skewEstimate = *skewEst;
128     obj->skewDataIndex++;
129   } else {
130     *skewEst = obj->skewEstimate;
131   }
132 
133   return err;
134 }
135 
EstimateSkew(const int * rawSkew,int size,int deviceSampleRateHz,float * skewEst)136 int EstimateSkew(const int* rawSkew,
137                  int size,
138                  int deviceSampleRateHz,
139                  float* skewEst) {
140   const int absLimitOuter = (int)(0.04f * deviceSampleRateHz);
141   const int absLimitInner = (int)(0.0025f * deviceSampleRateHz);
142   int i = 0;
143   int n = 0;
144   float rawAvg = 0;
145   float err = 0;
146   float rawAbsDev = 0;
147   int upperLimit = 0;
148   int lowerLimit = 0;
149   float cumSum = 0;
150   float x = 0;
151   float x2 = 0;
152   float y = 0;
153   float xy = 0;
154   float xAvg = 0;
155   float denom = 0;
156   float skew = 0;
157 
158   *skewEst = 0;  // Set in case of error below.
159   for (i = 0; i < size; i++) {
160     if ((rawSkew[i] < absLimitOuter && rawSkew[i] > -absLimitOuter)) {
161       n++;
162       rawAvg += rawSkew[i];
163     }
164   }
165 
166   if (n == 0) {
167     return -1;
168   }
169   assert(n > 0);
170   rawAvg /= n;
171 
172   for (i = 0; i < size; i++) {
173     if ((rawSkew[i] < absLimitOuter && rawSkew[i] > -absLimitOuter)) {
174       err = rawSkew[i] - rawAvg;
175       rawAbsDev += err >= 0 ? err : -err;
176     }
177   }
178   assert(n > 0);
179   rawAbsDev /= n;
180   upperLimit = (int)(rawAvg + 5 * rawAbsDev + 1);  // +1 for ceiling.
181   lowerLimit = (int)(rawAvg - 5 * rawAbsDev - 1);  // -1 for floor.
182 
183   n = 0;
184   for (i = 0; i < size; i++) {
185     if ((rawSkew[i] < absLimitInner && rawSkew[i] > -absLimitInner) ||
186         (rawSkew[i] < upperLimit && rawSkew[i] > lowerLimit)) {
187       n++;
188       cumSum += rawSkew[i];
189       x += n;
190       x2 += n * n;
191       y += cumSum;
192       xy += n * cumSum;
193     }
194   }
195 
196   if (n == 0) {
197     return -1;
198   }
199   assert(n > 0);
200   xAvg = x / n;
201   denom = x2 - xAvg * x;
202 
203   if (denom != 0) {
204     skew = (xy - xAvg * y) / denom;
205   }
206 
207   *skewEst = skew;
208   return 0;
209 }
210