Speex 一个开源的声学回声消除器(Acoustic Echo Cancellation)

在一般的VOIP软件或视频会议系统中,假设我们只有A和B两个人在通话,首先,A的声音传给B,B然后用喇叭放出来,而这时B的MIC呢则会采集到喇叭放出来的声音,然后传回给A,如果这个传输的过程中时延足够大,A就会听到一个和自己刚才说过的话一样的声音,这就是回声,声学回声消除器的作用就是在B端对B采集到的声音进行处理,把采集到声音包含的A的声音去掉再传给A,这样,A就不会听到自己说过的话了。
声学回声消除的原理我就不说了,这在网上有很多文档,网上缺少的是实现,所以,我在这把一个开源的声学回声消除器介绍一下,希望对有些有人用,如果有人知道怎么把这消除器用的基于实时流的VOIP软件中,希望能一起分享一下。
这个声学回声消除器是一个著名的音频编解码器speex中的一部分,1.1.9版本后的回声消除器才起作用,以前版本的都不行,我用的也是这个版本,测试表明,用同一个模拟文件,它有效果比INTEL IPP库4.1版中的声学回声消除器的还要好。
先说编译。首先,从 www.speex.org 上下载speex1.1.9的源代码,解压,打开speex/win32/libspeex中的libspeex.dsw,这个工作区里有两个工程,一个是libspeex,另一个是libspeex_dynamic。然后,将libspeex中的mdf.c文件添加到工程libspeex中,编译即可。
以下是我根据文档封装的一个类,里面有一个测试程序: //file name: speexEC.h
#ifndef SPEEX_EC_H
#define SPEEX_EC_H
#include
#include
#include "speex/speex_echo.h"
#include "speex/speex_preprocess.h"
class CSpeexEC
{
public:
CSpeexEC();
~CSpeexEC();
void Init(int frame_size=160, int filter_length=1280, int sampling_rate=8000);
void DoAEC(short *mic, short *ref, short *out);

protected:
void Reset();

private:
bool      m_bHasInit;
SpeexEchoState*   m_pState;
    SpeexPreprocessState* m_pPreprocessorState;
int      m_nFrameSize;
int      m_nFilterLen;
int      m_nSampleRate;
float*      m_pfNoise;
};

#endif

//fine name:speexEC.cpp
#include "SpeexEC.h"

CSpeexEC::CSpeexEC()
{
m_bHasInit   = false;
m_pState   = NULL;
m_pPreprocessorState  = NULL;
m_nFrameSize   = 160;
m_nFilterLen   = 160*8;
m_nSampleRate   = 8000;
m_pfNoise   = NULL;
}

CSpeexEC::~CSpeexEC()
{
Reset();
}

void CSpeexEC::Init(int frame_size, int filter_length, int sampling_rate)
{
Reset();

if (frame_size<=0 || filter_length<=0 || sampling_rate<=0)
{
  m_nFrameSize  =160;
  m_nFilterLen  = 160*8;
  m_nSampleRate = 8000;
}
else
{
  m_nFrameSize  =frame_size;
  m_nFilterLen  = filter_length;
  m_nSampleRate = sampling_rate;
}

m_pState = speex_echo_state_init(m_nFrameSize, m_nFilterLen);
m_pPreprocessorState = speex_preprocess_state_init(m_nFrameSize, m_nSampleRate);
m_pfNoise = new float[m_nFrameSize+1];
m_bHasInit = true;
}

void CSpeexEC::Reset()
{
if (m_pState != NULL)
{
  speex_echo_state_destroy(m_pState);
  m_pState = NULL;
}
if (m_pPreprocessorState != NULL)
{
  speex_preprocess_state_destroy(m_pPreprocessorState);
  m_pPreprocessorState = NULL;
}
if (m_pfNoise != NULL)
{
  delete []m_pfNoise;
  m_pfNoise = NULL;
}
m_bHasInit = false;
}

void CSpeexEC:DoAEC(short* mic, short* ref, short* out)
{
if (!m_bHasInit)
  return;

speex_echo_cancel(m_pState, mic, ref, out, m_pfNoise);
    speex_preprocess(m_pPreprocessorState, (__int16 *)out, m_pfNoise);
   
}

可以看出,这个回声消除器类很简单,只要初始化一下就可以调用了。但是,要注意的是,传给回声消除器的两个声音信号,必须同步得非常的好,就是说,在B端,接收到A说的话以后,要把这些话音数据传给回声消除器做参考,然后再传给声卡,声卡再放出来,这有一段延时,这时,B再采集,然后传给回声消除器,与那个参考数据比较,从采集到的数据中把频域和参考数据相同的部分消除掉。如果传给消除器的两个信号同步得不好,即两个信号找不到频域相同的部分,就没有办法进行消除了。
测试程序:

#define NN 160
void main()
{
FILE* ref_fd, *mic_fd, *out_fd;
short ref[NN], mic[NN], out[NN];
ref_fd = fopen ("ref.pcm", "rb"); //打开参考文件,即要消除的声音
mic_fd = fopen ("mic.pcm",  "rb");//打开mic采集到的声音文件,包含回声在里面
out_fd = fopen ("echo.pcm", "wb");//消除了回声以后的文件

CSpeexEC ec;
ec.Init();

while (fread(mic, 1, NN*2, mic_fd))
   {
      fread(ref, 1, NN*2, ref_fd); 
      ec.DoAEC(mic, ref, out);
      fwrite(out, 1, NN*2, out_fd);
   }
 
   fclose(ref_fd);
   fclose(mic_fd);
   fclose(out_fd);
}

  以上的程序是用文件来模拟回声和MIC,但在实时流中是大不一样的,在一般的VOIP软件中,接收对方的声音并传到声卡中播放是在一个线程中进行的,而采集本地的声音并传送到对方又是在另一个线程中进行的,而声学回声消除器在对采集到的声音进行回声消除的同时,还需要播放线程中的数据作为参考,而要同步这两个线程中的数据是非常困难的,因为稍稍有些不同步,声学回声消除器中的自适应滤波器就会发散,不但消除不了回声,还会破坏原始采集到的声音,使被破坏的声音难以分辨。我做过好多尝试,始终无法用软件来实现对这两个线程中的数据进行同步,导致实现失败,希望有经验的网友们一起分享一下这方面的经验。



示例代码:


Sample code

This section shows sample code for encoding and decoding speech using the Speex API. The commands can be used to encode and decode a file by calling: 
% sampleenc in_file.sw | sampledec out_file.sw
where both files are raw (no header) files encoded at 16 bits per sample (in the machine natural endianness).

sampleenc.c

sampleenc takes a raw 16 bits/sample file, encodes it and outputs a Speex stream to stdout. Note that the packing used is NOT compatible with that of speexenc/speexdec.

#include 
#include 
/*The frame size in hardcoded for this sample code but it doesn't have to be*/
#define FRAME_SIZE 160
int main(int argc, char **argv)
{
char *inFile;
FILE *fin;
short in[FRAME_SIZE];
float input[FRAME_SIZE];
char cbits[200];
int nbBytes;
/*Holds the state of the encoder*/
void *state;
/*Holds bits so they can be read and written to by the Speex routines*/
SpeexBits bits;
int i, tmp;
/*Create a new encoder state in narrowband mode*/
state = speex_encoder_init(&speex_nb_mode);
/*Set the quality to 8 (15 kbps)*/
tmp=8;
speex_encoder_ctl(state, SPEEX_SET_QUALITY, &tmp);
inFile = argv[1];
fin = fopen(inFile, "r");
/*Initialization of the structure that holds the bits*/
speex_bits_init(&bits);
while (1)
{
/*Read a 16 bits/sample audio frame*/
fread(in, sizeof(short), FRAME_SIZE, fin);
if (feof(fin))
break;
/*Copy the 16 bits values to float so Speex can work on them*/
for (i=0;i 
  

sampledec.c

sampledec reads a Speex stream from stdin, decodes it and outputs it to a raw 16 bits/sample file. Note that the packing used is NOT compatible with that of speexenc/speexdec.

#include 
#include 
/*The frame size in hardcoded for this sample code but it doesn't have to be*/
#define FRAME_SIZE 160
int main(int argc, char **argv)
{
char *outFile;
FILE *fout;
/*Holds the audio that will be written to file (16 bits per sample)*/
short out[FRAME_SIZE];
/*Speex handle samples as float, so we need an array of floats*/
float output[FRAME_SIZE];
char cbits[200];
int nbBytes;
/*Holds the state of the decoder*/
void *state;
/*Holds bits so they can be read and written to by the Speex routines*/
SpeexBits bits;
int i, tmp;
/*Create a new decoder state in narrowband mode*/
state = speex_decoder_init(&speex_nb_mode);
/*Set the perceptual enhancement on*/
tmp=1;
speex_decoder_ctl(state, SPEEX_SET_ENH, &tmp);
outFile = argv[1];
fout = fopen(outFile, "w");
/*Initialization of the structure that holds the bits*/
speex_bits_init(&bits);
while (1)
{
/*Read the size encoded by sampleenc, this part will likely be
different in your application*/
fread(&nbBytes, sizeof(int), 1, stdin);
fprintf (stderr, "nbBytes: %d/n", nbBytes);
if (feof(stdin))
break;
/*Read the "packet" encoded by sampleenc*/
fread(cbits, 1, nbBytes, stdin);
/*Copy the data into the bit-stream struct*/
speex_bits_read_from(&bits, cbits, nbBytes);
/*Decode the data*/
speex_decode(state, &bits, output);
/*Copy from float to short (16 bits) for output*/
for (i=0;i 
  
 
  
http://blog.csdn.net/liulina603/article/details/19353429

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