al_set_audio_stream_pan man page
al_set_audio_stream_pan — Allegro 5 API
#include <allegro5/allegro_audio.h> bool al_set_audio_stream_pan(ALLEGRO_AUDIO_STREAM *stream, float val)
Set the pan value on an audio stream. A value of -1.0 means to play the stream only through the left speaker; +1.0 means only through the right speaker; 0.0 means the sample is centre balanced. A special value ALLEGRO_AUDIO_PAN_NONE(3) disables panning and plays the stream at its original level. This will be louder than a pan value of 0.0.
Returns true on success, false on failure. Will fail if the audio stream is attached directly to a voice.