1 /*
2  * Copyrightm (C) 2010 The Android Open Source Project
3  *
4  * Licensed under the Apache License, Version 2.0 (the "License");
5  * you may not use this file except in compliance with the License.
6  * You may obtain a copy of the License at
7  *
8  *      http://www.apache.org/licenses/LICENSE-2.0
9  *
10  * Unless required by applicable law or agreed to in writing, software
11  * distributed under the License is distributed on an "AS IS" BASIS,
12  * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
13  * See the License for the specific language governing permissions and
14  * limitations under the License.
15  */
16 
17 #include <stdio.h>
18 #include <string.h>
19 #include <stdint.h>
20 #include <string.h>
21 #include <math.h>
22 
23 #define LOG_TAG "Echo"
24 #include <utils/Log.h>
25 
26 #include "EchoSuppressor.h"
27 
28 // It is very difficult to do echo cancellation at this level due to the lack of
29 // the timing information of the samples being played and recorded. Therefore,
30 // for the first release only echo suppression is implemented.
31 
32 // The algorithm is derived from the "previous works" summarized in
33 //   A new class of doubletalk detectors based on cross-correlation,
34 //   J Benesty, DR Morgan, JH Cho, IEEE Trans. on Speech and Audio Processing.
35 // The method proposed in that paper is not used because of its high complexity.
36 
37 // It is well known that cross-correlation can be computed using convolution,
38 // but unfortunately not every mobile processor has a (fast enough) FPU. Thus
39 // we use integer arithmetic as much as possible and do lots of bookkeeping.
40 // Again, parameters and thresholds are chosen by experiments.
41 
EchoSuppressor(int sampleCount,int tailLength)42 EchoSuppressor::EchoSuppressor(int sampleCount, int tailLength)
43 {
44     tailLength += sampleCount * 4;
45 
46     int shift = 0;
47     while ((sampleCount >> shift) > 1 && (tailLength >> shift) > 256) {
48         ++shift;
49     }
50 
51     mShift = shift + 4;
52     mScale = 1 << shift;
53     mSampleCount = sampleCount;
54     mWindowSize = sampleCount >> shift;
55     mTailLength = tailLength >> shift;
56     mRecordLength = tailLength * 2 / sampleCount;
57     mRecordOffset = 0;
58 
59     mXs = new uint16_t[mTailLength + mWindowSize];
60     memset(mXs, 0, sizeof(*mXs) * (mTailLength + mWindowSize));
61     mXSums = new uint32_t[mTailLength];
62     memset(mXSums, 0, sizeof(*mXSums) * mTailLength);
63     mX2Sums = new uint32_t[mTailLength];
64     memset(mX2Sums, 0, sizeof(*mX2Sums) * mTailLength);
65     mXRecords = new uint16_t[mRecordLength * mWindowSize];
66     memset(mXRecords, 0, sizeof(*mXRecords) * mRecordLength * mWindowSize);
67 
68     mYSum = 0;
69     mY2Sum = 0;
70     mYRecords = new uint32_t[mRecordLength];
71     memset(mYRecords, 0, sizeof(*mYRecords) * mRecordLength);
72     mY2Records = new uint32_t[mRecordLength];
73     memset(mY2Records, 0, sizeof(*mY2Records) * mRecordLength);
74 
75     mXYSums = new uint32_t[mTailLength];
76     memset(mXYSums, 0, sizeof(*mXYSums) * mTailLength);
77     mXYRecords = new uint32_t[mRecordLength * mTailLength];
78     memset(mXYRecords, 0, sizeof(*mXYRecords) * mRecordLength * mTailLength);
79 
80     mLastX = 0;
81     mLastY = 0;
82     mWeight = 1.0f / (mRecordLength * mWindowSize);
83 }
84 
~EchoSuppressor()85 EchoSuppressor::~EchoSuppressor()
86 {
87     delete [] mXs;
88     delete [] mXSums;
89     delete [] mX2Sums;
90     delete [] mXRecords;
91     delete [] mYRecords;
92     delete [] mY2Records;
93     delete [] mXYSums;
94     delete [] mXYRecords;
95 }
96 
run(int16_t * playbacked,int16_t * recorded)97 void EchoSuppressor::run(int16_t *playbacked, int16_t *recorded)
98 {
99     // Update Xs.
100     for (int i = mTailLength - 1; i >= 0; --i) {
101         mXs[i + mWindowSize] = mXs[i];
102     }
103     for (int i = mWindowSize - 1, j = 0; i >= 0; --i, j += mScale) {
104         uint32_t sum = 0;
105         for (int k = 0; k < mScale; ++k) {
106             int32_t x = playbacked[j + k] << 15;
107             mLastX += x;
108             sum += ((mLastX >= 0) ? mLastX : -mLastX) >> 15;
109             mLastX -= (mLastX >> 10) + x;
110         }
111         mXs[i] = sum >> mShift;
112     }
113 
114     // Update XSums, X2Sums, and XRecords.
115     for (int i = mTailLength - mWindowSize - 1; i >= 0; --i) {
116         mXSums[i + mWindowSize] = mXSums[i];
117         mX2Sums[i + mWindowSize] = mX2Sums[i];
118     }
119     uint16_t *xRecords = &mXRecords[mRecordOffset * mWindowSize];
120     for (int i = mWindowSize - 1; i >= 0; --i) {
121         uint16_t x = mXs[i];
122         mXSums[i] = mXSums[i + 1] + x - xRecords[i];
123         mX2Sums[i] = mX2Sums[i + 1] + x * x - xRecords[i] * xRecords[i];
124         xRecords[i] = x;
125     }
126 
127     // Compute Ys.
128     uint16_t ys[mWindowSize];
129     for (int i = mWindowSize - 1, j = 0; i >= 0; --i, j += mScale) {
130         uint32_t sum = 0;
131         for (int k = 0; k < mScale; ++k) {
132             int32_t y = recorded[j + k] << 15;
133             mLastY += y;
134             sum += ((mLastY >= 0) ? mLastY : -mLastY) >> 15;
135             mLastY -= (mLastY >> 10) + y;
136         }
137         ys[i] = sum >> mShift;
138     }
139 
140     // Update YSum, Y2Sum, YRecords, and Y2Records.
141     uint32_t ySum = 0;
142     uint32_t y2Sum = 0;
143     for (int i = mWindowSize - 1; i >= 0; --i) {
144         ySum += ys[i];
145         y2Sum += ys[i] * ys[i];
146     }
147     mYSum += ySum - mYRecords[mRecordOffset];
148     mY2Sum += y2Sum - mY2Records[mRecordOffset];
149     mYRecords[mRecordOffset] = ySum;
150     mY2Records[mRecordOffset] = y2Sum;
151 
152     // Update XYSums and XYRecords.
153     uint32_t *xyRecords = &mXYRecords[mRecordOffset * mTailLength];
154     for (int i = mTailLength - 1; i >= 0; --i) {
155         uint32_t xySum = 0;
156         for (int j = mWindowSize - 1; j >= 0; --j) {
157             xySum += mXs[i + j] * ys[j];
158         }
159         mXYSums[i] += xySum - xyRecords[i];
160         xyRecords[i] = xySum;
161     }
162 
163     // Compute correlations.
164     int latency = 0;
165     float corr2 = 0.0f;
166     float varX = 0.0f;
167     float varY = mY2Sum - mWeight * mYSum * mYSum;
168     for (int i = mTailLength - 1; i >= 0; --i) {
169         float cov = mXYSums[i] - mWeight * mXSums[i] * mYSum;
170         if (cov > 0.0f) {
171             float varXi = mX2Sums[i] - mWeight * mXSums[i] * mXSums[i];
172             float corr2i = cov * cov / (varXi * varY + 1);
173             if (corr2i > corr2) {
174                 varX = varXi;
175                 corr2 = corr2i;
176                 latency = i;
177             }
178         }
179     }
180     //ALOGI("corr^2 %.5f, var %8.0f %8.0f, latency %d", corr2, varX, varY,
181     //        latency * mScale);
182 
183     // Do echo suppression.
184     if (corr2 > 0.1f && varX > 10000.0f) {
185         int factor = (corr2 > 1.0f) ? 0 : (1.0f - sqrtf(corr2)) * 4096;
186         for (int i = 0; i < mSampleCount; ++i) {
187             recorded[i] = recorded[i] * factor >> 16;
188         }
189     }
190 
191     // Increase RecordOffset.
192     ++mRecordOffset;
193     if (mRecordOffset == mRecordLength) {
194         mRecordOffset = 0;
195     }
196 }
197