Different audio levels between SOURCE_RELATIVE True/False

[email protected] Fri, 3 Sep 2010 14:58:09 -0400

Newsgroups	gmane.comp.lib.openal
Message-ID	<[email protected]>

Hi,
I'm looking into switching between SOURCE_RELATIVE True/False to allow
some form of split screen functionality.

In my testing I have noticed that there is a difference in audio output
level when switching between the two modes, and by the sound of it there
is some clipping/overload happening in the engine.

A small test application is attached which shows this problem. I have a
single sound source traveling around a circle, the listener is on the
circle and will hear the source traveling past.

With SOURCE_RELATIVE False the audio output is much loud/overloaded when
the source is closest to listener.


I tried to limit/equalise this with MAX_GAIN/CONE_ANGLES, but these did
not fix the problem.

Any suggestions as to what is wrong?
Simon.

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circle_test.c (text/x-csrc, 3.9 KB)

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

#include <AL/al.h>
#include <AL/alc.h>
#include <AL/alut.h>

#define POS_UPDATE 0.1	// 10Hz
#define SPLIT_UPDATE 20

#define RADIUS 100
#define ROTSPEED 20 	// seconds to complete rotation

#define MULTI_CONTEXT 0
#define MAX_SPLIT 2

double time_now(void)
{
	struct timeval my_time;

	gettimeofday(&my_time, NULL);
	return (double) my_time.tv_sec + ((double) my_time.tv_usec/1000000);
}

// Global defines
ALuint Buffer[MAX_SPLIT];
ALuint Source[MAX_SPLIT];

// Initial Positions
ALfloat SourcePos[] = { 0.0, RADIUS, 0.0 };
ALfloat SourceVel[] = { 0.0, 0.0, 0.0 };

// Listener positions (around a circle)
ALfloat ListenerMulti[][3] = { 	
				{ 0.0, -RADIUS, 0.0 },
				{ 0.0, -RADIUS, 0.0 },
				{ -RADIUS, 0.0, 0.0 },
				{ 0.0, RADIUS, 0.0 },
				{ RADIUS, 0.0, 0.0 }	  
			};  

ALfloat ListenerVel[] = { 0.0, 0.0, 0.0 };
ALfloat ListenerOri[] = { 0.0, 0.0, 0.0,  0.0, 1.0, 0.0 };


int main(int argc, char *argv[])
{
	double start_time, current_time, next_pos_update, next_split_update;
	float angle, x, y;

	ALint play;
	ALenum format;
	ALsizei size;
	ALvoid* data;
	ALsizei freq;
	ALuint repeat;

	int loop, mode=0;

	// Create a device with multiple contexts on it
	ALCdevice * pSoundcard;
	ALCcontext * pContextStereo;
	ALCcontext * pContext[MAX_SPLIT];

	pSoundcard = alcOpenDevice(NULL);
	pContext[0] = alcCreateContext(pSoundcard, NULL);	// Stereo

	alcMakeContextCurrent(pContext[0]);

	// Load the wav data.
	alGenBuffers(1, &Buffer[0]);
	alutLoadWAVFile((ALbyte*)"tone1.wav", &format, &data, &size, &freq, &repeat);
	alBufferData(Buffer[0], format, data, size, freq);
	alutUnloadWAV(format, data, size, freq);

	// Set listener positions
	printf("Setting up stereo context:\n");
	printf("Setting location %f, %f, %f\n\n", ListenerMulti[0][0], ListenerMulti[0][1], ListenerMulti[0][2]);
	alListenerfv(AL_POSITION,    ListenerMulti[0]);
	alListenerfv(AL_VELOCITY,    ListenerVel);
	alListenerfv(AL_ORIENTATION, ListenerOri);

	alGenSources(1, &Source[0]);

	alSourcei (Source[0], AL_BUFFER,   Buffer[0]);
	alSourcef (Source[0], AL_PITCH,    1.0      );
	alSourcef (Source[0], AL_GAIN,     1.0      );
	alSourcei (Source[0], AL_LOOPING,  AL_TRUE);

	alSourcefv(Source[0], AL_POSITION, SourcePos);
	alSourcefv(Source[0], AL_VELOCITY, SourceVel);
	alSourcei (Source[0], AL_SOURCE_RELATIVE, AL_TRUE);

#if 0
	// attempt to limit gain
	alSourcef (Source[0], AL_MAX_GAIN, 0.7      );
	alSourcef (Source[0], AL_CONE_INNER_ANGLE, 360.0 );
	alSourcef (Source[0], AL_CONE_OUTER_ANGLE, 360.0 );
#endif

	alcMakeContextCurrent(pContext[0]);
	alSourcePlay(Source[0]);

	// Set up initial time reference
	start_time = time_now();
	next_pos_update = POS_UPDATE;
	next_split_update = 0;

	while (1) {
		// Get current time
		current_time = time_now() - start_time;

		// Do we need to switch to next listener?
		if (current_time > next_split_update) {
			switch (mode) {
				case 0:
					printf("\nAL_SOURCE_RELATIVE = AL_TRUE -> Stereo sound into L/R\n\n");

					// Stereo
					alcMakeContextCurrent(pContext[0]);
					alSourcei (Source[0], AL_SOURCE_RELATIVE, AL_TRUE);
					mode++;
					break;
				case 1:
					printf("\nAL_SOURCE_RELATIVE = AL_FALSE -> Mono into both ears\n\n");
					alSourcei (Source[0], AL_SOURCE_RELATIVE, AL_FALSE);
				default:
					mode = 0;
			}


			// prescision is not required here
			next_split_update += SPLIT_UPDATE;
		}

		// Reposition Source
		if (current_time > next_pos_update) {
			angle = ((current_time / ROTSPEED) - (int)(current_time / ROTSPEED)) * 2 * 3.141592653589793;

			SourcePos[0] = RADIUS * sin(angle);
			SourcePos[1] = RADIUS * cos(angle);

			alcMakeContextCurrent(pContext[0]);
			alSourcefv(Source[0], AL_POSITION, SourcePos);
			alSourcefv(Source[0], AL_VELOCITY, SourceVel);

			printf("%f: %f, %f, %f, %f\n",current_time, angle, SourcePos[0],SourcePos[1],SourcePos[2]);
			while (next_pos_update < current_time)
				next_pos_update = next_pos_update + POS_UPDATE;
		}
	}
}