al_set_mixer_postprocess_callback - Allegro 5 API

       Sets  a  post-processing  filter  function that’s called after the attached streams have been mixed.  The
       buffer’s format will be whatever the mixer was created with.  The sample count and user-data  pointer  is
       also passed.

              Note: The callback is called from a dedicated audio thread.

Allegro reference manual                                              al_set_mixer_postprocess_callback(3alleg5)

       al_set_mixer_postprocess_callback - Allegro 5 API

              #include <allegro5/allegro_audio.h>

              bool al_set_mixer_postprocess_callback(ALLEGRO_MIXER *mixer,
                 void (*pp_callback)(void *buf, unsigned int samples, void *data),
                 void *pp_callback_userdata)