An aside resembles a soliloquy in that it does not have an addressee on stage. It differs from the soliloquy in that the speaker is not alone on stage(nor does he imagine he is alone). As a result, an aside bears even less mimetic relationship to real life than a conventionalized soliloquy. This kind of aside is called a conventionalized monological aside. It enables the author to:
If we look at Sweeney Todd we see an example of this in a section of There's No Place Like London:
There's a whole in the world like a great black pit,
And the vermin of the world inhabit it.
When Todd sings this, he's not addressing anyone on stage. It is more like an interior mumbling, reflected in the music, by repeated notes, with little melodic change. Judging by Anthony's reaction, Anthony, who at that moment is the only one on stage with Todd, hasn't even heard this mumbling.