> At a certain point, Spotify contacted Perry’s music manager to explain how the service had transformed his client from autoworker to house music luminary in months. It was simple: It had a lot to do with Spotify’s music-recommendation technology. The company keeps track of what you listen to. Then it uses algorithms to see which other playlists contain the same songs—and other songs that are on those lists but not on yours.
Although Release Radar apparently does analyse sounds as it doesn't have the playlist history to access.
There is bunch of info out there about this
The magic that makes Spotify’s Discover Weekly playlists so damn good