转自:
http://blog.csdn.net/iflychenyang/article/details/11680449
线性叠加后求平均
优点:不会产生溢出,噪音较小;
缺点:衰减过大,影响通话质量;
short remix(short buffer1,short buffer2)
{
int value = buffer1 + buffer2;
return (short)(value/2);
}
归一化混音(自适应加权混音算法)
思路:
使用更多的位数(32 bit)来表示音频数据的一个样本,混完音后在想办法降低其振幅,使其仍旧分布在16 bit所能表示的范围之内,这种方法叫做归一法.
方法:
为避免发生溢出,使用一个可变的衰减因子对语音进行衰减。这个衰减因子也就代表语音的权重,衰减因子随着音频数据的变化而变化,所以称为自适应加权混音。当溢出时,衰减因子较小,使得溢出的数据在衰减后能够处于临界值以内,而在没有溢出时,又让衰减因子慢慢增大,使数据较为平缓的变化.
代码:
void Mix(char sourseFile[10][SIZE_AUDIO_FRAME],int number,char *objectFile)
{
int const MAX=32767;
int const MIN=-32768;
double f=1;
int output;
int i = 0,j = 0;
for (i=0;i2;i++)
{
int temp=0;
for (j=0;jshort*)(sourseFile[j]+i*2);
}
output=(int)(temp*f);
if (output>MAX)
{
f=(double)MAX/(double)(output);
output=MAX;
}
if (outputdouble)MIN/(double)(output);
output=MIN;
}
if (f<1)
{
f+=((double)1-f)/(double)32;
}
*(short*)(objectFile+i*2)=(short)output;
}
}
下面是我从newlc上找到的一个关于PCM脉冲编码的音频信号的混音实现,其中包含了一个关键的混音算法!
if( data1 < 0 && data2 < 0)
date_mix = data1+data2 - (data1 * data2 / -(pow(2,16-1)-1));
else
date_mix = data1+data2 - (data1 * data2 / (pow(2,16-1)-1));
切割时间片,重采样算法
可以把各个通道的声音叠到一起,让声音的采样率按倍增加,如果提高声音的播放频率,声音可以正常的播放,声音实现了叠加;如果不想修改声音的播放输出频率,可以通过声音的重采样后输出自己想要的输出频率;
下面是上面的混音的测试代码:
#include
#include
#include
#define IN_FILE1 "1.wav"
#define IN_FILE2 "2.wav"
#define OUT_FILE "remix.pcm"
#define SIZE_AUDIO_FRAME (2)
void Mix(char sourseFile[10][SIZE_AUDIO_FRAME],int number,char *objectFile)
{
int const MAX=32767;
int const MIN=-32768;
double f=1;
int output;
int i = 0,j = 0;
for (i=0;i2;i++)
{
int temp=0;
for (j=0;jshort*)(sourseFile[j]+i*2);
}
output=(int)(temp*f);
if (output>MAX)
{
f=(double)MAX/(double)(output);
output=MAX;
}
if (outputdouble)MIN/(double)(output);
output=MIN;
}
if (f<1)
{
f+=((double)1-f)/(double)32;
}
*(short*)(objectFile+i*2)=(short)output;
}
}
int main()
{
FILE * fp1,*fp2,*fpm;
fp1 = fopen(IN_FILE1,"rb");
fp2 = fopen(IN_FILE2,"rb");
fpm = fopen(OUT_FILE,"wb");
short data1,data2,date_mix;
int ret1,ret2;
char sourseFile[10][2];
while(1)
{
ret1 = fread(&data1,2,1,fp1);
ret2 = fread(&data2,2,1,fp2);
*(short*) sourseFile[0] = data1;
*(short*) sourseFile[1] = data2;
if(ret1>0 && ret2>0)
{
Mix(sourseFile,2,(char *)&date_mix);
if(date_mix > pow(2,16-1) || date_mix < -pow(2,16-1))
printf("mix error
");
}
else if( (ret1 > 0) && (ret2==0))
{
date_mix = data1;
}
else if( (ret2 > 0) && (ret1==0))
{
date_mix = data2;
}
else if( (ret1 == 0) && (ret2 == 0))
{
break;
}
fwrite(&date_mix,2,1,fpm);
}
fclose(fp1);
fclose(fp2);
fclose(fpm);
printf("Done!
");
}