OpenAL Soft -- demonstration of binaural 3D audio

OpenAL Soft is a branch of OpenAL which has filtering implemented in software, and it also adds support for head-related transfer functions (HRTFs). HRTFs permit 3D auralization through stereo earphones.

So here follows an example of using OpenAL. One looping sound effect (footsteps) make a random walk through the world while you, the listener, stand still.


For the footsteps.raw, I did this:

Got the file from http://www.soundjay.com/footsteps/footsteps-4.wav

Then processed it using 'sox':
> sox footsteps-4.wav -b 16 footsteps.raw channels 1 rate 44100

/* footsteps.c
 *
 * To compile:
 *   gcc -o footsteps footsteps.c -lopenal
 *
 * Requires data "footsteps.raw", which is any signed-16bit
 * mono audio data (no header!); assumed samplerate is 44.1kHz.
 *
 */

#include <stdlib.h>
#include <stdio.h>
#include <unistd.h>  /* for usleep() */
#include <math.h>    /* for sqrtf() */
#include <time.h>    /* for time(), to seed srand() */

/* OpenAL headers */
#include <AL/al.h>
#include <AL/alc.h>
#include <AL/alext.h>

/* load a file into memory, returning the buffer and
 * setting bufsize to the size-in-bytes */
void* load( char *fname, long *bufsize ){
   FILE* fp = fopen( fname, "rb" );
   fseek( fp, 0L, SEEK_END );
   long len = ftell( fp );
   rewind( fp );
   void *buf = malloc( len );
   fread( buf, 1, len, fp );
   fclose( fp );
   *bufsize = len;
   return buf;
}

/* randomly displace 'a' by one meter +/- in x or z */
void randWalk( float *a ){
   int r = rand() & 0x3;
   switch(r){
      case 0: a[0]-= 1.; break;
      case 1: a[0]+= 1.; break;
      case 2: a[2]-= 1.; break;
      case 3: a[2]+= 1.; break;
   }
   printf("Walking to: %.1f,%.1f,%.1f\n",a[0],a[1],a[2]);
}

int main( int argc, char *argv[] ){
   /* current position and where to walk to... start just 1m ahead */
   float curr[3] = {0.,0.,-1.};
   float targ[3] = {0.,0.,-1.};

   /* initialize OpenAL context, asking for 44.1kHz to match HRIR data */
   ALCint contextAttr[] = {ALC_FREQUENCY,44100,0};
   ALCdevice* device = alcOpenDevice( NULL );
   ALCcontext* context = alcCreateContext( device, contextAttr );
   alcMakeContextCurrent( context );

   /* listener at origin, facing down -z (ears at 1.5m height) */
   alListener3f( AL_POSITION, 0., 1.5, 0. );
   alListener3f( AL_VELOCITY, 0., 0., 0. );
   float orient[6] = { /*fwd:*/ 0., 0., -1., /*up:*/ 0., 1., 0. };
   alListenerfv( AL_ORIENTATION, orient );

   /* this will be the source of ghostly footsteps... */
   ALuint source;
   alGenSources( 1, &source );
   alSourcef( source, AL_PITCH, 1. );
   alSourcef( source, AL_GAIN, 1. );
   alSource3f( source, AL_POSITION, curr[0],curr[1],curr[2] );
   alSource3f( source, AL_VELOCITY, 0.,0.,0. );
   alSourcei( source, AL_LOOPING, AL_TRUE );

   /* allocate an OpenAL buffer and fill it with monaural sample data */
   ALuint buffer;
   alGenBuffers( 1, &buffer );
   {
      long dataSize;
      const ALvoid* data = load( "footsteps.raw", &dataSize );
      /* for simplicity, assume raw file is signed-16b at 44.1kHz */
      alBufferData( buffer, AL_FORMAT_MONO16, data, dataSize, 44100 );
      free( (void*)data );
   }
   alSourcei( source, AL_BUFFER, buffer );

   /* state initializations for the upcoming loop */
   srand( (int)time(NULL) );
   float dt = 1./60.;
   float vel = 0.8 * dt;
   float closeEnough = 0.05;

   /** BEGIN! **/
   alSourcePlay( source );

   fflush( stderr ); /* in case OpenAL reported an error earlier */

   /* loop forever... walking to random, adjacent, integer coordinates */
   for(;;){
      float dx = targ[0]-curr[0];
      float dy = targ[1]-curr[1];
      float dz = targ[2]-curr[2];
      float dist = sqrtf( dx*dx + dy*dy + dz*dz );
      if( dist < closeEnough ) randWalk(targ);
      else{
         float toVel = vel/dist;
         float v[3] = {dx*toVel, dy*toVel, dz*toVel};
         curr[0]+= v[0];
         curr[1]+= v[1];
         curr[2]+= v[2];

         alSource3f( source, AL_POSITION, curr[0],curr[1],curr[2] );
         alSource3f( source, AL_VELOCITY, v[0],v[1],v[2] );
         usleep( (int)(1e6*dt) );
      }
   }

   /* cleanup that should be done when you have a proper exit... ;) */
   alDeleteSources( 1, &source );
   alDeleteBuffers( 1, &buffer );
   alcDestroyContext( context );
   alcCloseDevice( device );

   return 0;
}