Inner monologue is pretty much exactly that. The ability to internalize sound and voice that is not hallucinatory or accusatory. It's literally at a very simple level being able to just think of yourself saying something and you thinking it you hear it. On the other end of the spectrum you can basically make any sound or voice at will audible in your head.

I am on that far end of the spectrum where I could just make anything happen in my head visually or auditorily.