I'm a UK-based singer-songwriter. I've had a demo of a duet I wrote professionally recorded by two session singers in the US, as my voice wasn't what I wanted for this one. Piano track is essentially as I wrote it, there's an added cello part, and the vocal melody/harmonies/lyrics are all mine. But what's the right/legal thing to do re: releasing this on Spotify - do I have to pay the singers/cellist a % if and when I clear the costs of recording, etc? And if so, does this mean that I'm in effect becoming my own publisher? I know nothing of how this all works, but I do know this is by far the best and most commercial song I've written to date - and it's a Christmas one, so I'd really like to put it out there and earn some of the production costs back.
There's a long and solid history around "demo" recordings. Demos are...well...for demonstration. For shopping. For a work-in-progress reality check. The session musicians get a different, lesser scale for "demo" work than they do with "master" work. ("master" being a track intended for release/distribution). It has of course happened many times that a demo ends up being better than the master, and gets released.
In a formalized contract situation (read: union), what would happen is that the session would be retroactively upgraded to a master session from being a demo session, and the players would get a bump. Those hired players would not typically get royalties though. In today's world, the notion of back-end royalties is essentially moot, or even (not)amusing.
Mind you, I'm talking USA...UK is not quite the same kind of animal, though it's similar.