混音算法

http://blog.youkuaiyun.com/chinabinlang/article/details/8086443

混音算法：

 

混音算法

Hi !!!!

I am not sure weather I have fully understood your question or not, I persume that you are asking 
"How can we mix two or more audio stream", If this is the question then I am explaning below the 
mixing of the two audio stream (You Can Mix More Audio Stream),

Step 1, 

Get the Raw data of the two files, (Example, of the sample 8bit and 8Kh, means one sample is of
8bit)


Step 2 

Let the two audio signal be A and B respectively, the range is between 0 and 255. Where A and B are the
Sample Values (Each raw data) And store the resultant into the Y

If Both the samples Values are possitve

Y = A + B - A * B / 255 

Where Y is the resultant signal which contains both signal A and B, merging two audio streams into single 
stream by this method solves the problem of overflow and information loss to an extent. 


If the range of 8-bit sampling is between -127 to 128 

If both A and B are negative Y = A +B - (A * B / (-127)) 
Else Y = A + B - A * B / 128 


Similarly for the nbit (ex 16bit data)

For n-bit sampling audio signal 


If both A and B are negative Y = A + B - (A * B / (-(2 pow(n-1) -1))) 
Else Y = A + B - (A * B / (2 pow(n-1)) 


Step 3.

Add the Header to the Resultant (mixed) data and play back.

If some thing is unclear and ambigious let me know.

Regards
Ranjeet Gupta.

还有简单C程序示意代码，但是其中包含了核心算法：

#include <stdio.h>
#include <string.h>
#include <stdlib.h>
#include <math.h>

int main(int argc,char *argv[]) {
char mixname[255];
FILE *pcm1, *pcm2, *mix;
char sample1, sample2;
int value;

pcm1 = fopen(argv[1],"r");
pcm2 = fopen(argv[2],"r");

strcpy (mixname, argv[1]);
strcat (mixname, "_temp.wav");
mix = fopen(mixname, "w");

while(!feof(pcm1)) {

sample1 = fgetc(pcm1);
sample2 = fgetc(pcm2);

if ((sample1 < 0) && (sample2 < 0)) {
value = sample1 + sample2 - (sample1 * sample2 / -(pow(2,16-1)-1));
}else{
value = sample1 + sample2 - (sample1 * sample2 / (pow(2,16-1)-1));
}

fputc(value, mix);
}


fclose(pcm1);
fclose(pcm2);
fclose(mix);

return 0;
}