应用speex进行音频去噪，speex功能很强大，因为opus的出现，用speex进行编码/解码的人几乎没有了，但是用speex来进行降噪，去除回声，增益还是很多。

这里用speex进行音频去噪，主要用如下几个关键点:

1，准确设置pcm音频的音频采样率，和帧长度，

st = speex_preprocess_state_init(FRAME_SIZE, FRAME_SAMPLERATE);//初始化

2，设置降噪参数，其中DENOISE_DB默认是-25，单位是dB(分贝)；

int denoise = 1;

int noiseSuppress = DENOISE_DB;

speex_preprocess_ctl(st, SPEEX_PREPROCESS_SET_DENOISE, &denoise); //降噪

speex_preprocess_ctl(st, SPEEX_PREPROCESS_SET_NOISE_SUPPRESS, &noiseSuppress); //设置噪声的dB

源代码如下，main函数参数一是原始pcm文件名，参数二是去噪后的pcm文件名

#ifdef HAVE_CONFIG_H

#include "../config.h"

#endif

#include "speex/speex_preprocess.h"

#include

#define FRAME_SIZE 1152

#define FRAME_SAMPLERATE 32000

#define DENOISE_DB (-90)

int main(int argn, char* argv[]) {

char* szInFilename = NULL;

char* szOutFilename = NULL;

FILE* pInFileHandle = NULL;

FILE* pOutFileHandle = NULL;

short in[FRAME_SAMPLERATE];

int i;

SpeexPreprocessState *st;

int count=0;

float f;

printf("starting....\r\n");

if(argn != 3){

printf("please input 2 parameters\r\n");

return -1;

}

memset((void*)empty, 0, sizeof(empty));

szInFilename = argv[1];

szOutFilename = argv[2];

pInFileHandle = fopen(szInFilename, "rb");

if(!pInFileHandle){

printf("open file %s error\r\n", szInFilename);

return -2;

}

pOutFileHandle = fopen(szOutFilename, "wb");

if(!pOutFileHandle){

printf("open file %s error\r\n", szOutFilename);

fclose(pInFileHandle);

return -3;

}

st = speex_preprocess_state_init(FRAME_SIZE, FRAME_SAMPLERATE);

int denoise = 1;

int noiseSuppress = DENOISE_DB;

speex_preprocess_ctl(st, SPEEX_PREPROCESS_SET_DENOISE, &denoise); //降噪

speex_preprocess_ctl(st, SPEEX_PREPROCESS_SET_NOISE_SUPPRESS, &noiseSuppress); //设置噪声的dB

i=0;

speex_preprocess_ctl(st, SPEEX_PREPROCESS_SET_AGC, &i);

i=8000;

speex_preprocess_ctl(st, SPEEX_PREPROCESS_SET_AGC_LEVEL, &i);

i=0;

speex_preprocess_ctl(st, SPEEX_PREPROCESS_SET_DEREVERB, &i);

f=.0;

speex_preprocess_ctl(st, SPEEX_PREPROCESS_SET_DEREVERB_DECAY, &f);

f=.0;

speex_preprocess_ctl(st, SPEEX_PREPROCESS_SET_DEREVERB_LEVEL, &f);

int vad = 1;

int vadProbStart = 80;

int vadProbContinue = 65;

speex_preprocess_ctl(st, SPEEX_PREPROCESS_SET_VAD, &vad); //静音检测

speex_preprocess_ctl(st, SPEEX_PREPROCESS_SET_PROB_START , &vadProbStart); //Set probability required for the VAD to go from silence to voice

speex_preprocess_ctl(st, SPEEX_PREPROCESS_SET_PROB_CONTINUE, &vadProbContinue); //Set probability required for the VAD to stay in the voice state (integer percent)

while (1)

{

int vad;

int iLen = fread(in, sizeof(short), FRAME_SIZE, pInFileHandle);

if(iLen <= 0){

break;

}

if (feof(pInFileHandle))

break;

vad = speex_preprocess_run(st, in);

if(vad != 0){

printf("speech.\r\n");

fwrite(in, sizeof(short), FRAME_SIZE, pOutFileHandle);

}else{

printf("slience############################\r\n");

fwrite(in, sizeof(short), FRAME_SIZE, pOutFileHandle);

}

count++;

}

speex_preprocess_state_destroy(st);

fclose(pInFileHandle);

fclose(pOutFileHandle);

return 0;

}

编译的Makefile如下：

OBJS = test.o

CC = gcc

CFLAGS = -Wall -O -g -D HAVE_CONFIG_H

LD = /usr/local/lib/libspeexdsp.a

INCLUDE_PATH = /usr/local/include/speex

test : $(OBJS)

$(CC) $(OBJS) $(LD) -lm -I$(INCLUDE_PATH) -o test

test.o : test.c

$(CC) $(CFLAGS) -I$(INCLUDE_PATH) -c test.c

clean:

rm -rf *.o test

而编译speexdsp-1.2rc3库文件的脚本如下:

./configure --prefix=/usr/local --enable-shared --enable-static --enable-sse

make

make install

去噪后的效果，感觉不是很理想，原因应该是speex的去噪功能比较简单，基本上是以来声音分贝来进行去噪，所以不是很准确。

接下来去研究一下Audacity的源码，看看是否能提高降噪效果。

相关网址：

https://github.com/audacity/audacity

https://github.com/audacity/audacity/blob/ae5d29a04815cc41ccf36ef765a9f75636b8bd21/src/effects/NoiseRemoval.cpp

(runner42)