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 43 void* WebRtcAec_CreateResampler() { 44 return malloc(sizeof(AecResampler)); 45 } 46 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 60 void WebRtcAec_FreeResampler(void* resampInst) { 61 AecResampler* obj = (AecResampler*)resampInst; 62 free(obj); 63 } 64 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 } 116 117 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 } 135 136 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
