I have a friend and musical colleague who is a prodigy (kind of Mozart-like) and he works out 8 part harmonies in his head like that, but doesn't even practice them or sing them out loud until he is ready for his one takes.

He blows people's minds.

"No, I'm ready," he says, as he steps up to the mic. "I can hear it. Just hit record." Then he does it, eight times in a row.

You play it all back it and it sounds like a choral ensemble that practiced for a week.

That is not me. There are a few people like that and it is trippy.

I think the rest of us have to work it out.