al_attach_mixer_to_voice man page
al_attach_mixer_to_voice — Allegro 5 API
#include <allegro5/allegro_audio.h> bool al_attach_mixer_to_voice(ALLEGRO_MIXER *mixer, ALLEGRO_VOICE *voice)
Attaches a mixer to a voice. It must have the same frequency and channel configuration, but the depth may be different.
Returns true on success, false on failure.
Allegro reference manual