A vocoder is a good approximation for what a cochlear implant's speech processor does.

There's been one person who was implanted, who had their natural hearing return for unknown reasons. So they can hear both cochlear, and quite well naturally in the same ear.

This let researchers at Arizona State University ask basically: what sounds most like the cochlear input? The various samples involving their research about 15 years ago are probably your best bet for what it sounds like.

Some people with musical training before retain the ability to hear arbitrary melodies with perfect pitch. Some do not.

There is basically no polyphony.