no-reply@allegro.cc (BulletDave4) — Sat, 18 Jun 2011 19:20:08 +0000

For the past few days, I have been working hard on adding an audio system to my game. So far, I have managed to set-up two different audio systems.

The first is specialized for songs since they can be large. Note: all of my audio files are .ogg files. For the songs, I load them into an ALLEGRO_AUDIO_STREAM.

The second is designed for sound effects. Note: they are also .ogg files. This time around I use an ALLEGRO_SAMPLE_INSTANCE.

For some odd reason, when I play a song with multiple sound effects, I get static. I tried on other computers and on my headphones and its the same issue.

I tried isolating the issue with little luck. All I noticed is that if I play a single sound, be it a song, or a sound effect, it will be clear, and the moment I begin adding other audio, it begins to fill-up with static.

Note: For each song I am creating a new AUDIO_STREAM, MIXER, and VOICE. For each sound, I am creating a new MIXER, VOICE, SAMPLE, SAMPLE INSTANCE, AUDIO STREAM. I don't really know if its a bad thing having that many mixers/voices/samples.

Here is how I create my song class:

#SelectExpand
  1CSong::CSong( const char* filename, uint frequency,
  2           size_t bufferCount, uint samples ) :
  3  m_mixer(NULL), m_voice(NULL), m_stream(NULL)
  4{
  5  m_voice = al_create_voice( frequency, ALLEGRO_DEPTH_INT16,
  6                             ALLEGRO_CHANNEL_CONF_2 );
  7  m_mixer = al_create_mixer( frequency, ALLEGRO_DEPTH_FLOAT32,
  8                             ALLEGRO_CHANNEL_CONF_2 );
  9  al_attach_mixer_to_voice( m_mixer, m_voice );
 10
 11  m_stream = al_load_audio_stream( filename, bufferCount, samples );
 12  al_attach_audio_stream_to_mixer( m_stream, m_mixer );
 13
 14  al_set_audio_stream_playmode( m_stream, ALLEGRO_PLAYMODE_LOOP );
 15
 16  setPlay( false );
 17}

And here is how I create my sound class:

#SelectExpand
  1CSound::CSound( const char* filename ) :
m_mixer(NULL), m_voice(NULL),
m_sample(NULL), m_sampleInstance(NULL),
m_position(0), m_audioStream(NULL)
  5{
m_voice = al_create_voice( 44100, ALLEGRO_AUDIO_DEPTH_INT16,   
               ALLEGRO_CHANNEL_CONF_2 );
m_mixer = al_create_mixer( 44100, ALLEGRO_AUDIO_DEPTH_FLOAT32, 
               ALLEGRO_CHANNEL_CONF_2 );
al_attach_mixer_to_voice( m_mixer, m_voice );
 11
m_sampleInstance = al_create_sample_instance( NULL );
m_sample = al_load_sample( filename );
al_set_sample( m_sampleInstance, m_sample );
 15
al_attach_sample_instance_to_mixer( m_sampleInstance, m_mixer );
al_set_sample_instance_playmode( m_sampleInstance, ALLEGRO_PLAYMODE_ONCE );
al_play_sample_instance( m_sampleInstance );
 19}

Additional info, here are my settings:
-Frequency: 44100
-Buffer Count: 2
-Samples: 2048
-Reserved Samples: 50

Why might it be creating static???

no-reply@allegro.cc (Matthew Leverton) — Sat, 18 Jun 2011 19:52:25 +0000

Generally you only need a single voice and mixer. You definitely should not be creating one per song.

If you call al_reserve_samples() that will automatically create a mixer. You can then call al_get_default_mixer(). Also, with al_reserve_samples() you can simply call al_play_sample() without creating your own instances... that's what it's for, after all.

no-reply@allegro.cc (BulletDave4) — Sat, 18 Jun 2011 20:32:44 +0000

I did exactly as you told me and it works great! No more static noise.

Thanks a bunch

no-reply@allegro.cc (Peter Wang) — Sun, 19 Jun 2011 08:11:54 +0000

Fixed in r14803. This was due to the use of a global mixing buffer which obviously is wrong when two mixers run in parallel (which only happens when there are multiple voices).

Not that you need multiple voices.

Multiple audio stream causes static?