That sort of describes the Pandora approach. Each song has a set of "genes" that describe its tone, musical instrumentation, key signature, time signature, rhyt

That sort of describes the Pandora approach. Each song has a set of "genes" that describe its tone, musical instrumentation, key signature, time signature, rhythmic syncopation, etc. these genes are then used to find similar music. I've found it to be quite pleasing to discover new music when it's seeded with a relatively uncommon song that I like. For instance, I added "Going Through Changes" by "Army of Me", and its recommendations included songs from bands I'd never heard of and actually enjoyed, like Radford, Red (a Christian band, one, as an atheist, I wouldn't ever have browsed on my own, but ended up really enjoying), Maxeen, Black Lab, and Brand New. Each had "genes" that made their algorithm align them with the seed song. I don't use it much right now - I find myself in a cycle of discovery and then stubborn re-listening of the same four or five albums - but I expect I'll go back to it the next time I'm back in that exploratory mood.