al_set_audio_stream_pan
bool al_set_audio_stream_pan(ALLEGRO_AUDIO_STREAM *stream, float val)
Set the pan value on a sample instance. A value of -1.0 means to play the sample only through the left speaker; +1.0 means only through the right speaker; 0.0 means the sample is centre balanced.
Returns true on success, false on failure. Will fail if the sample instance is attached directly to a voice.
See also: al_get_audio_stream_playing.
Examples: ex_synth