Question

I need help getting started with libsndfile.

I have four .wav files (all the same sample rate).

I want to join the first two together,then the next two together,

Then mix the resulting 2 .wav files into one.

Answer 1

For mixing two wav files.

#include <cstdio>
#include <sndfile.h>
#include <windows.h>
#include <cstdlib>
#include <cmath>

#define BUFFER_LEN 1024
#define MAX_CHANNELS 6

static void data_processing (double *data, int count, int channels) ;

int main (void) {

  static double data [BUFFER_LEN] ;
  static double data2 [BUFFER_LEN] ;
  static double outdata [BUFFER_LEN] ;

  SNDFILE *infile, *outfile, *infile2 ;
  SF_INFO sfinfo ;
  int readcount ;
  SF_INFO sfinfo2 ;
  int readcount2 ;

  const char *infilename = "inputOne.wav" ;
  const char *infilename2 = "inputTwo.wav" ;
  const char *outfilename = "output.wav" ;

  if (! (infile = sf_open (infilename, SFM_READ, &sfinfo))) {
    /* Open failed so print an error message. */
    printf ("Not able to open input file %s.\n", infilename) ;

    /* Print the error message from libsndfile. */
    puts (sf_strerror (NULL)) ;
    return 1 ;
  } ;

  if (sfinfo.channels > MAX_CHANNELS) {
    printf ("Not able to process more than %d channels\n", MAX_CHANNELS) ;
    return 1 ;
  } ;

  if (! (infile2 = sf_open (infilename2, SFM_READ, &sfinfo2))) {
    /* Open failed so print an error message. */
    printf ("Not able to open input file %s.\n", infilename2) ;

    /* Print the error message from libsndfile. */
    puts (sf_strerror (NULL)) ;
    return 1 ;
  } ;

  if (sfinfo2.channels > MAX_CHANNELS) {
    printf ("Not able to process more than %d channels\n", MAX_CHANNELS) ;
    return 1 ;
  } ;

  /* Open the output file. */
  if (! (outfile = sf_open (outfilename, SFM_WRITE, &sfinfo))) {
    printf ("Not able to open output file %s.\n", outfilename) ;
    puts (sf_strerror (NULL)) ;
    return 1 ;
  } ;

  while ((readcount = sf_read_double (infile, data, BUFFER_LEN)) &&
         (readcount2 = sf_read_double (infile2, data2, BUFFER_LEN))) { 
    data_processing (data, readcount, sfinfo.channels) ;
data_processing(data2, readcount2, sfinfo2.channels) ;

    for(int i=0; i < 1024;++i) {
  outdata[i] = (data[i] + data2[i]) -(data[i])*(data2[i])/65535;
    }

    sf_write_double (outfile, outdata , readcount) ;
  } ;

  /* Close input and output files. */
  sf_close (infile) ;
  sf_close (infile2) ;
  sf_close (outfile) ;
  system("PAUSE");
  return 0 ;
} /* main */

static void data_processing(double *data, int count, int channels) { 
  double channel_gain [MAX_CHANNELS] = { 0.5, 0.8, 0.1, 0.4, 0.4, 0.9 } ;
  int k, chan ;

  for (chan = 0 ; chan < channels ; chan ++)
    for (k = chan ; k < count ; k+= channels)
      data [k] *= channel_gain [chan] ;

  return ;
} /* data_processing */

This is how i am mixing two simple wav files which are 16 bit signals.

First of all audio mixing is not easy as one might think. There might be many ambiguities after joining two signals. In my case it is working just fine as much as i need it, but if you need exact results you might need to google more for exact superimposing signals over each other.

For joining two wav files you can just read your first wav file copy the data in the result wav file and finally append the data of the second wav file to the result wav file.

This link might also be useful for you
http://www.vttoth.com/digimix.htm