1. speex的降噪模块的简介
speex的语音处理模块要使用独立于 speex codec库的libspeexdsp 库。
这个分离的库是在1.2版本后实现；
它这库包括了： 预处理，回声消除，jitter buffer 和重采样模块；
在Unix/Linux环境下，使用 -lspeexdsp -lm 来编译和链接。
和libspeex一样，库libspeexdsp的库函数都是可重入函数。
但它不是线程安全的，所以在多个线程中使用同一个实例时，必须加个线程安全锁。
NOTE:
所谓就是允许被的函数。
函数的递归调用是 指当一个函数正被调用尚未返回时，又直接或间接调用函数本身。
一般的函数不能做到这样，只有重入函数才允许递归调用.
2. 下载与编译
$ tar -zxvf
$ cd speexdsp-1.2rc3
$./configure --prefix=/data/speexdsp-1.2rc3-install/ --enable-static --disable-shared --with-pic
$ make && make install
3. API简介
预处理模块需要添加头文件：
#include
创建实例:
SpeexPreprocessState *preprocess_state = speex_preprocess_state_init(frame_size,sampling_rate);
参数： frame_size ， 建议设置成编码器相同的值。
对于每一个输入帧，调用处理的函数：
speex_preprocess_run(preprocess_state, audio_frame);
参数： audio_frame ， 即是输入，也是输出。
在某些场景下，有些降噪的数据并不想输出，可以下面的API:
它会更新处理器内部的状态，但不会将降噪后的数据输出，这样可以节省一些计算量：
speex_preprocess_estimate_update(preprocess_state, audio_frame);
使用下面API来改变进行预处理器的状态设置，更多的参数见下面的一节：
speex_preprocess_ctl(preprocess_state, request, ptr);
实例销毁 :
speex_preprocess_state_destroy(preprocess_state);
3.1 Preprocessor options
As with the codec, the preprocessor also has options that can be controlled using an ioctl()-like call. The available options are:
SPEEX_PREPROCESS_SET_DENOISE Turns denoising on(1) or off(2) (spx_int32_t)
SPEEX_PREPROCESS_GET_DENOISE Get denoising status (spx_int32_t)
SPEEX_PREPROCESS_SET_AGC Turns automatic gain control (AGC) on(1) or off(2) (spx_int32_t)
SPEEX_PREPROCESS_GET_AGC Get AGC status (spx_int32_t)
SPEEX_PREPROCESS_SET_VAD Turns voice activity detector (VAD) on(1) or off(2) (spx_int32_t)
SPEEX_PREPROCESS_GET_VAD Get VAD status (spx_int32_t)
SPEEX_PREPROCESS_SET_AGC_LEVEL
SPEEX_PREPROCESS_GET_AGC_LEVEL
SPEEX_PREPROCESS_SET_DEREVERB Turns reverberation removal on(1) or off(2) (spx_int32_t)
SPEEX_PREPROCESS_GET_DEREVERB Get reverberation removal status (spx_int32_t)
SPEEX_PREPROCESS_SET_DEREVERB_LEVEL Not working yet, do not use
SPEEX_PREPROCESS_GET_DEREVERB_LEVEL Not working yet, do not use
SPEEX_PREPROCESS_SET_DEREVERB_DECAY Not working yet, do not use
SPEEX_PREPROCESS_GET_DEREVERB_DECAY Not working yet, do not use
SPEEX_PREPROCESS_SET_PROB_START
SPEEX_PREPROCESS_GET_PROB_START
SPEEX_PREPROCESS_SET_PROB_CONTINUE
SPEEX_PREPROCESS_GET_PROB_CONTINUE
SPEEX_PREPROCESS_SET_NOISE_SUPPRESS Setmaximumattenuation of the noise in dB (negativespx_int32_t)
SPEEX_PREPROCESS_GET_NOISE_SUPPRESS Getmaximumattenuation of the noise in dB (negativespx_int32_t)
SPEEX_PREPROCESS_SET_ECHO_SUPPRESS Setmaximumattenuation of the residual echo in dB (negative spx_int32_t)
SPEEX_PREPROCESS_GET_ECHO_SUPPRESS Setmaximumattenuation of the residual echo in dB (negativespx_int32_t)
SPEEX_PREPROCESS_SET_ECHO_SUPPRESS_ACTIVE Set maximum attenuation of the echo in dB when near
end is active (negative spx_int32_t)
SPEEX_PREPROCESS_GET_ECHO_SUPPRESS_ACTIVE Set maximum attenuation of the echo in dB when near
end is active (negative spx_int32_t)
SPEEX_PREPROCESS_SET_ECHO_STATE Set the associated echo canceller for residual echo suppression (pointer
or NULL for no residual echo suppression)
SPEEX_PREPROCESS_GET_ECHO_STATE Get the associated echo canceller (pointer)
4. 应用实例
C语言实现的音频降噪代码如下。
代码中采样率、音频帧大小需要根据实际情况设置，
HEADLEN是WAV格式的文件头，占44个字节，这44个字节是不需要处理的，不然文件头会损坏，
导致得到的结果无法播放。
如果是PCM数据，则没有这个头，直接输入指定长度的数据就行；
noiseSuppress的值可以控制减除的噪声强度，负值越小，噪声去除的强度越大，
同时会造成原声的失真，需要作出权衡。
#include
#include
#include
#include
#include
#include
#define HEADLEN 44
#define SAMPLE_RATE (48000)
#define SAMPLES_PER_FRAME (1024)
#define FRAME_SIZE (SAMPLES_PER_FRAME * 1000/ SAMPLE_RATE)
#define FRAME_BYTES (SAMPLES_PER_FRAME)
int main()
{
size_t n = 0;
FILE *inFile, *outFile;
fopen_s(&inFile, "./audio/input01L.wav", "rb");
fopen_s(&outFile, "./audio/output01L.wav", "wb");
char *headBuf = (char*)malloc(HEADLEN);
char *dataBuf = (char*)malloc(FRAME_BYTES * 2 );
memset(headBuf, 0, HEADLEN);
memset(dataBuf, 0, FRAME_BYTES);
assert(headBuf != NULL);
assert(dataBuf != NULL);
SpeexPreprocessState *state = speex_preprocess_state_init(1024, SAMPLE_RATE);
int denoise = 1;
int noiseSuppress = -25;
speex_preprocess_ctl(state, SPEEX_PREPROCESS_SET_DENOISE, &denoise);
speex_preprocess_ctl(state, SPEEX_PREPROCESS_SET_NOISE_SUPPRESS, &noiseSuppress);
int i;
i = 0;
speex_preprocess_ctl(state, SPEEX_PREPROCESS_SET_AGC, &i);
i = 80000;
speex_preprocess_ctl(state, SPEEX_PREPROCESS_SET_AGC_LEVEL, &i);
i = 0;
speex_preprocess_ctl(state, SPEEX_PREPROCESS_SET_DEREVERB, &i);
float f = 0;
speex_preprocess_ctl(state, SPEEX_PREPROCESS_SET_DEREVERB_DECAY, &f);
f = 0;
speex_preprocess_ctl(state, SPEEX_PREPROCESS_SET_DEREVERB_LEVEL, &f);
//静音检测，效果一般
/*
int vad = 1;
int vadProbStart = 80;
int vadProbContinue = 65;
speex_preprocess_ctl(state, SPEEX_PREPROCESS_SET_VAD, &vad);
speex_preprocess_ctl(state, SPEEX_PREPROCESS_SET_PROB_START, &vadProbStart);
speex_preprocess_ctl(state, SPEEX_PREPROCESS_SET_PROB_CONTINUE, &vadProbContinue);
*/
bool flag = true;
while (1)
{
if (flag == true)
{
flag = false;
n = fread(headBuf, 1, HEADLEN, inFile);
if (n == 0)
break;
fwrite(headBuf, 1, HEADLEN, outFile);
}
else
{
n = fread(dataBuf, 1, SAMPLES_PER_FRAME, inFile);
if (n == 0)
break;
speex_preprocess_run(state, (spx_int16_t*)(dataBuf));
fwrite(dataBuf, 1, SAMPLES_PER_FRAME, outFile);
}
}
free(headBuf);
free(dataBuf);
fclose(inFile);
fclose(outFile);
speex_preprocess_state_destroy(state);
return 0;
}