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/*
* Copyrightm (C) 2010 The Android Open Source Project
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
#include <stdio.h>
#include <string.h>
#include <stdint.h>
#include <math.h>
#define LOG_TAG "Echo"
#include <utils/Log.h>
#include "EchoSuppressor.h"
// It is very difficult to do echo cancellation at this level due to the lack of
// the timing information of the samples being played and recorded. Therefore,
// for the first release only echo suppression is implemented.
// The algorithm is derived from the "previous works" summarized in
// A new class of doubletalk detectors based on cross-correlation,
// J Benesty, DR Morgan, JH Cho, IEEE Trans. on Speech and Audio Processing.
// The method proposed in that paper is not used because of its high complexity.
// It is well known that cross-correlation can be computed using convolution,
// but unfortunately not every mobile processor has a (fast enough) FPU. Thus
// we use integer arithmetic as much as possible and do lots of bookkeeping.
// Again, parameters and thresholds are chosen by experiments.
EchoSuppressor::EchoSuppressor(int sampleCount, int tailLength)
{
tailLength += sampleCount * 4;
int shift = 0;
while ((sampleCount >> shift) > 1 && (tailLength >> shift) > 256) {
++shift;
}
mShift = shift + 4;
mScale = 1 << shift;
mSampleCount = sampleCount;
mWindowSize = sampleCount >> shift;
mTailLength = tailLength >> shift;
mRecordLength = tailLength * 2 / sampleCount;
mRecordOffset = 0;
mXs = new uint16_t[mTailLength + mWindowSize];
memset(mXs, 0, sizeof(*mXs) * (mTailLength + mWindowSize));
mXSums = new uint32_t[mTailLength];
memset(mXSums, 0, sizeof(*mXSums) * mTailLength);
mX2Sums = new uint32_t[mTailLength];
memset(mX2Sums, 0, sizeof(*mX2Sums) * mTailLength);
mXRecords = new uint16_t[mRecordLength * mWindowSize];
memset(mXRecords, 0, sizeof(*mXRecords) * mRecordLength * mWindowSize);
mYSum = 0;
mY2Sum = 0;
mYRecords = new uint32_t[mRecordLength];
memset(mYRecords, 0, sizeof(*mYRecords) * mRecordLength);
mY2Records = new uint32_t[mRecordLength];
memset(mY2Records, 0, sizeof(*mY2Records) * mRecordLength);
mXYSums = new uint32_t[mTailLength];
memset(mXYSums, 0, sizeof(*mXYSums) * mTailLength);
mXYRecords = new uint32_t[mRecordLength * mTailLength];
memset(mXYRecords, 0, sizeof(*mXYRecords) * mRecordLength * mTailLength);
mLastX = 0;
mLastY = 0;
mWeight = 1.0f / (mRecordLength * mWindowSize);
}
EchoSuppressor::~EchoSuppressor()
{
delete [] mXs;
delete [] mXSums;
delete [] mX2Sums;
delete [] mXRecords;
delete [] mYRecords;
delete [] mY2Records;
delete [] mXYSums;
delete [] mXYRecords;
}
void EchoSuppressor::run(int16_t *playbacked, int16_t *recorded)
{
// Update Xs.
for (int i = mTailLength - 1; i >= 0; --i) {
mXs[i + mWindowSize] = mXs[i];
}
for (int i = mWindowSize - 1, j = 0; i >= 0; --i, j += mScale) {
uint32_t sum = 0;
for (int k = 0; k < mScale; ++k) {
int32_t x = playbacked[j + k] << 15;
mLastX += x;
sum += ((mLastX >= 0) ? mLastX : -mLastX) >> 15;
mLastX -= (mLastX >> 10) + x;
}
mXs[i] = sum >> mShift;
}
// Update XSums, X2Sums, and XRecords.
for (int i = mTailLength - mWindowSize - 1; i >= 0; --i) {
mXSums[i + mWindowSize] = mXSums[i];
mX2Sums[i + mWindowSize] = mX2Sums[i];
}
uint16_t *xRecords = &mXRecords[mRecordOffset * mWindowSize];
for (int i = mWindowSize - 1; i >= 0; --i) {
uint16_t x = mXs[i];
mXSums[i] = mXSums[i + 1] + x - xRecords[i];
mX2Sums[i] = mX2Sums[i + 1] + x * x - xRecords[i] * xRecords[i];
xRecords[i] = x;
}
// Compute Ys.
uint16_t ys[mWindowSize];
for (int i = mWindowSize - 1, j = 0; i >= 0; --i, j += mScale) {
uint32_t sum = 0;
for (int k = 0; k < mScale; ++k) {
int32_t y = recorded[j + k] << 15;
mLastY += y;
sum += ((mLastY >= 0) ? mLastY : -mLastY) >> 15;
mLastY -= (mLastY >> 10) + y;
}
ys[i] = sum >> mShift;
}
// Update YSum, Y2Sum, YRecords, and Y2Records.
uint32_t ySum = 0;
uint32_t y2Sum = 0;
for (int i = mWindowSize - 1; i >= 0; --i) {
ySum += ys[i];
y2Sum += ys[i] * ys[i];
}
mYSum += ySum - mYRecords[mRecordOffset];
mY2Sum += y2Sum - mY2Records[mRecordOffset];
mYRecords[mRecordOffset] = ySum;
mY2Records[mRecordOffset] = y2Sum;
// Update XYSums and XYRecords.
uint32_t *xyRecords = &mXYRecords[mRecordOffset * mTailLength];
for (int i = mTailLength - 1; i >= 0; --i) {
uint32_t xySum = 0;
for (int j = mWindowSize - 1; j >= 0; --j) {
xySum += mXs[i + j] * ys[j];
}
mXYSums[i] += xySum - xyRecords[i];
xyRecords[i] = xySum;
}
// Compute correlations.
float corr2 = 0.0f;
int latency = 0;
float varY = mY2Sum - mWeight * mYSum * mYSum;
for (int i = mTailLength - 1; i >= 0; --i) {
float varX = mX2Sums[i] - mWeight * mXSums[i] * mXSums[i];
float cov = mXYSums[i] - mWeight * mXSums[i] * mYSum;
float c2 = cov * cov / (varX * varY + 1);
if (c2 > corr2) {
corr2 = c2;
latency = i;
}
}
//LOGI("correlation^2 = %.10f, latency = %d", corr2, latency * mScale);
// Do echo suppression.
if (corr2 > 0.1f) {
int factor = (corr2 > 1.0f) ? 0 : (1.0f - sqrtf(corr2)) * 4096;
for (int i = 0; i < mSampleCount; ++i) {
recorded[i] = recorded[i] * factor >> 16;
}
}
// Increase RecordOffset.
++mRecordOffset;
if (mRecordOffset == mRecordLength) {
mRecordOffset = 0;
}
}
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