al_get_default_mixer - Allegro 5 API

       Return  the  default mixer, or NULL if one has not been set.  Although different configurations of mixers
       and voices can be used, in most cases a single mixer attached to a voice is what you want.   The  default
       mixer is used by al_play_sample(3alleg5).

       al_get_default_mixer - Allegro 5 API

al_reserve_samples(3alleg5),            al_play_sample(3alleg5),           al_set_default_mixer(3alleg5),
       al_restore_default_mixer(3alleg5)

Allegro reference manual                                                           al_get_default_mixer(3alleg5)

              #include <allegro5/allegro_audio.h>

              ALLEGRO_MIXER *al_get_default_mixer(void)