Reggie Ugwu, at Buzzfeed, pulled together a fantastic feature, bringing you behind the scenes at Apple Music, Spotify, and Google Play.

When he’s choosing your music for you, Carl Chery, 37, is in Culver City, California, sitting at his desk in an office with no signage, trying to decide whether Drake and Future’s “Jumpman” (jumpman, jumpman, jumpman) has jumped the shark. Or sometimes he’s at home in his one-bedroom apartment on the border of West Hollywood and Beverly Hills, walking around in his living room with new Gucci Mane blasting from a Beats Pill. Or at the gym going for a morning run on the treadmill, thinking about your gym and your treadmill, listening through headphones for changes in tempo and tone: Will this song push you through the pain? Is that one too long on the buildup?

I’ve always wondered how they pull these playlists together. This piece answers a lot of questions.