1 /* 2 * Copyright (c) 2011 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 clock 12 * skew by resampling the farend signal. 13 */ 14 15 #include <assert.h> 16 #include <stdlib.h> 17 #include <string.h> 18 #include <math.h> 19 20 #include "resampler.h" 21 #include "aec_core.h" 22 23 enum { kFrameBufferSize = FRAME_LEN * 4 }; 24 enum { kEstimateLengthFrames = 400 }; 25 26 typedef struct { 27 short buffer[kFrameBufferSize]; 28 float position; 29 30 int deviceSampleRateHz; 31 int skewData[kEstimateLengthFrames]; 32 int skewDataIndex; 33 float skewEstimate; 34 } resampler_t; 35 36 static int EstimateSkew(const int* rawSkew, 37 int size, 38 int absLimit, 39 float *skewEst); 40 41 int WebRtcAec_CreateResampler(void **resampInst) 42 { 43 resampler_t *obj = malloc(sizeof(resampler_t)); 44 *resampInst = obj; 45 if (obj == NULL) { 46 return -1; 47 } 48 49 return 0; 50 } 51 52 int WebRtcAec_InitResampler(void *resampInst, int deviceSampleRateHz) 53 { 54 resampler_t *obj = (resampler_t*) resampInst; 55 memset(obj->buffer, 0, sizeof(obj->buffer)); 56 obj->position = 0.0; 57 58 obj->deviceSampleRateHz = deviceSampleRateHz; 59 memset(obj->skewData, 0, sizeof(obj->skewData)); 60 obj->skewDataIndex = 0; 61 obj->skewEstimate = 0.0; 62 63 return 0; 64 } 65 66 int WebRtcAec_FreeResampler(void *resampInst) 67 { 68 resampler_t *obj = (resampler_t*) resampInst; 69 free(obj); 70 71 return 0; 72 } 73 74 int WebRtcAec_ResampleLinear(void *resampInst, 75 const short *inspeech, 76 int size, 77 float skew, 78 short *outspeech) 79 { 80 resampler_t *obj = (resampler_t*) resampInst; 81 82 short *y; 83 float be, tnew, interp; 84 int tn, outsize, mm; 85 86 if (size < 0 || size > 2 * FRAME_LEN) { 87 return -1; 88 } 89 90 // Add new frame data in lookahead 91 memcpy(&obj->buffer[FRAME_LEN + kResamplingDelay], 92 inspeech, 93 size * sizeof(short)); 94 95 // Sample rate ratio 96 be = 1 + skew; 97 98 // Loop over input frame 99 mm = 0; 100 y = &obj->buffer[FRAME_LEN]; // Point at current frame 101 102 tnew = be * mm + obj->position; 103 tn = (int) tnew; 104 105 while (tn < size) { 106 107 // Interpolation 108 interp = y[tn] + (tnew - tn) * (y[tn+1] - y[tn]); 109 110 if (interp > 32767) { 111 interp = 32767; 112 } 113 else if (interp < -32768) { 114 interp = -32768; 115 } 116 117 outspeech[mm] = (short) interp; 118 mm++; 119 120 tnew = be * mm + obj->position; 121 tn = (int) tnew; 122 } 123 124 outsize = mm; 125 obj->position += outsize * be - size; 126 127 // Shift buffer 128 memmove(obj->buffer, 129 &obj->buffer[size], 130 (kFrameBufferSize - size) * sizeof(short)); 131 132 return outsize; 133 } 134 135 int WebRtcAec_GetSkew(void *resampInst, int rawSkew, float *skewEst) 136 { 137 resampler_t *obj = (resampler_t*)resampInst; 138 int err = 0; 139 140 if (obj->skewDataIndex < kEstimateLengthFrames) { 141 obj->skewData[obj->skewDataIndex] = rawSkew; 142 obj->skewDataIndex++; 143 } 144 else if (obj->skewDataIndex == kEstimateLengthFrames) { 145 err = EstimateSkew(obj->skewData, 146 kEstimateLengthFrames, 147 obj->deviceSampleRateHz, 148 skewEst); 149 obj->skewEstimate = *skewEst; 150 obj->skewDataIndex++; 151 } 152 else { 153 *skewEst = obj->skewEstimate; 154 } 155 156 return err; 157 } 158 159 int EstimateSkew(const int* rawSkew, 160 const int size, 161 const int deviceSampleRateHz, 162 float *skewEst) 163 { 164 const int absLimitOuter = (int)(0.04f * deviceSampleRateHz); 165 const int absLimitInner = (int)(0.0025f * deviceSampleRateHz); 166 int i = 0; 167 int n = 0; 168 float rawAvg = 0; 169 float err = 0; 170 float rawAbsDev = 0; 171 int upperLimit = 0; 172 int lowerLimit = 0; 173 float cumSum = 0; 174 float x = 0; 175 float x2 = 0; 176 float y = 0; 177 float xy = 0; 178 float xAvg = 0; 179 float yAvg = 0; 180 float denom = 0; 181 float skew = 0; 182 183 *skewEst = 0; // Set in case of error below. 184 for (i = 0; i < size; i++) { 185 if ((rawSkew[i] < absLimitOuter && rawSkew[i] > -absLimitOuter)) { 186 n++; 187 rawAvg += rawSkew[i]; 188 } 189 } 190 191 if (n == 0) { 192 return -1; 193 } 194 assert(n > 0); 195 rawAvg /= n; 196 197 for (i = 0; i < size; i++) { 198 if ((rawSkew[i] < absLimitOuter && rawSkew[i] > -absLimitOuter)) { 199 err = rawSkew[i] - rawAvg; 200 rawAbsDev += err >= 0 ? err : -err; 201 } 202 } 203 assert(n > 0); 204 rawAbsDev /= n; 205 upperLimit = (int)(rawAvg + 5 * rawAbsDev + 1); // +1 for ceiling. 206 lowerLimit = (int)(rawAvg - 5 * rawAbsDev - 1); // -1 for floor. 207 208 n = 0; 209 for (i = 0; i < size; i++) { 210 if ((rawSkew[i] < absLimitInner && rawSkew[i] > -absLimitInner) || 211 (rawSkew[i] < upperLimit && rawSkew[i] > lowerLimit)) { 212 n++; 213 cumSum += rawSkew[i]; 214 x += n; 215 x2 += n*n; 216 y += cumSum; 217 xy += n * cumSum; 218 } 219 } 220 221 if (n == 0) { 222 return -1; 223 } 224 assert(n > 0); 225 xAvg = x / n; 226 yAvg = y / n; 227 denom = x2 - xAvg*x; 228 229 if (denom != 0) { 230 skew = (xy - xAvg*y) / denom; 231 } 232 233 *skewEst = skew; 234 return 0; 235 } 236
