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
42EchoSuppressor::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
85EchoSuppressor::~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
97void 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