A system is called audiovisual if all of its systematic functions take only immutable variants of logic step or cosmos, (const_logic_step or const cosmos&) and hence, whose side effects are limited to the private fields of the system.
Conventions
Since the definition of an audiovisual system effectively prohibits any alteration to our “application model”, it makes literally no sense to use it for anything else than for the “view” part of the application.
Thence the name audiovisual (sound is a part of view, too!).
For example, a particle system