[Discuss-gnuradio] GNU Stereo audio --> wave file

[Chuck Swiger]

Gang - Here's how to export two audio channels and get stereo wav, mp3,
etc.

Sound card audio ranges from -1 to 1 so we scale by 32768 (-32767 to
32768)
then combine two float streams to one complex stream and save to a
file:

----------------------------------------------------------------------

        

scale1 =
gr.multiply_const_ff(32767)

        

scale2 =
gr.multiply_const_ff(32767)

        

combine =
gr.float_to_complex ()

        

file_sink
= gr.file_sink (gr.sizeof_gr_complex, 
"fm_stereo_out")

#leave tail connect to audio_sink to listen and record at the same
time

        

self.connect
(tail[0], scale1)

        

self.connect
(tail[1], scale2)

        

self.connect
(scale1,(combine,0))

        

self.connect
(scale2,(combine,1))

        

self.connect
(combine,file_sink)
--------------------------------------------------------------------------

The secret sauce is the following which will convert the complex 2
channel float
format to "signed word" (two channel short) format that sox
understands:

--------------------------------------------------------------------------
/* convert double 4-byte float
(complex) data to 
   double 2-byte short numbers for 2 channel stereo 
*/

#include <stdio.h>

FILE *input_file, *output_file;
int i,int_j,int_k;
float j,k;

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

if ( argc < 4 ) {
   printf("\nUsage: raw2num <input file> <output
file> <number of samples>\n");
   printf("Exampel: ./raw2num fm_out_complex fm_out.sw
1920000\n");
   exit(1);
   }

input_file = fopen(argv[1],"r");
output_file = fopen(argv[2],"w");

for (i=0;i<atoi(argv[3]);i++) {
    fread(&j,4,1,input_file);
    fread(&k,4,1,input_file);
    int_j = (int) j;
    int_k = (int) k;
    fwrite(&int_j,2,1,output_file);
    fwrite(&int_k,2,1,output_file); 
    }

fclose(input_file);
fclose(output_file);
}

------------------------------------------------------------------------------------------------------

Not ready for prime time but works. Then run the output file thru
sox:

$ sox -r 32000 -c 2 fm_stereo_out.sw fm_stereo_out.wav

then you can load it into Cooledit/Audacity, convert to mp3, etc.
sample here:
http://webpages.charter.net/cswiger/fm_stereo.html

--Chuck