That bar is far too low - reductio ad absurdem, you could go as far as changing lyrics - or substituting an entirely different song - and if you'd never heard t

That bar is far too low - reductio ad absurdem, you could go as far as changing lyrics - or substituting an entirely different song - and if you'd never heard the song before you'd never know the difference. As for more subtle changes, what constitutes a "plausible sound" in any given context is an AI-complete problem. Sure on a particular song, you might get away with e.g. tinkering with the reverb a bit, or changing the tempo by 0.5% - but how can you possibly do that in the general case? Remember - all such changes have to be audibly salient to humans, because that's the only thing guaranteed to survive.