How Spotify’s Discover Weekly Works, From The Man Who Made It

**chinski** · 11-17-2015

How Spotify’s Discover Weekly Works, From The Man Who Made It

Have you checked your latest Discover Weekly playlist on Spotify yet? Go on. We’ll wait. Your new favourite band could be on there. Done? Anything good? Of course there was; there always is. But the real question is: how do they do it?

Spotify’s bespoke, auto-generated mixtape playlists have been brightening Monday mornings at Stuff HQ for a while now, so we decided to ask its creator, Matthew Ogle, how it actually works – and whether our penchant for Disney soundtracks was endangering our keenly moulded tastemaker status.

So how does it pick the songs?

“There's two parts to it. First, we look at all the music you've been playing on Spotify but we give more emphasis to the stuff you've been jamming on recently. Something that you played yesterday is probably more interesting to you than something you played six months ago. But the real core of it is looking at the relationships between songs based on what other users are playlisting around the songs that you've been listening to and essentially finding the missing ones – the ones you haven't heard yet, or maybe haven't heard much.”

And how does it know which ones I actually like?

“If you click through to the album or artist page and play it from there we'll pick up on that. If there are some songs on Discover Weekly that you save to your collection or add to a playlist of your own and then keep listening to after the week is up, we'll notice that too. But if you change your listening a bit for one week, you won't suddenly have a completely different Discover Weekly the next.”

Why does it keep including bands I already like?

“That is deliberate but it was a happy accident early on in developing Discover Weekly. It was meant to filter out everything that a listener already knew or had already played on Spotify but the first few versions had some bugs in the code and the playlists that we tested on employees had some songs, or at least some artists, that were in their listening histories. We reported it as a bug and the bug was patched. But it turns out staring at a list of 30 completely foreign songs is daunting. You need a way in, a reason to trust us, so we ended up reintroducing a bit of that familiarity.”

So hang on, if I only ever listen to my Discover Weekly playlist, won’t it eventually eat itself?

“No, is the short answer. Plays from within your Discover Weekly playlist don't count when we generate your subsequent week's Discover Weekly – and there's a good reason for that. We're saying "you might like this" and you're taking us at our word and trying stuff out, but there may be stuff in there that you don't like and just because you played it through Discover Weekly we shouldn't assume it's part of your taste. While you're in Discover Weekly it's sort of a safe space where you're off the record.”

Why is it only 30 songs long?

“Early prototypes had 50 and 100 tracks in but if a mate showed up on your doorstep with a 6-CD box set and said "I made this for you" it would be quite strange, right? There was a tipping point where it just didn't feel personal or human anymore. In a way you have less incentive to check stuff out from a list of 50 songs because it's hard to know where to begin or how to find a way in. We kept shortening it until it felt approachable and human. 30 songs means there’s enough to explore but it's not intimidating.”

Why does it overwrite itself every week?

“Without clogging up your sidebar with your past playlists there wasn't a simple way within the existing structure of the app to archive it. We looked at the time it would take to build a dedicated system for that versus just rolling without it and we thought there was something quite nice about the way it works. We've heard the request and we may make it easier in a future version to save your whole list, or provide a way to look back at previous ones, but the romantic in me also thinks that maybe this constraint, and the simplicity of the experience as a result of it being a bit more ephemeral, maybe there's something to that.”

Will it include stuff like the Frozen soundtrack, which I, er, play for my kids?

“No, there's stuff we'll filter right out. We made the decision early on in testing that we wouldn't include children's music. A lot of Spotify users are parents who play Disney tunes for the kids. They do a pretty good job of telling their parents when a new soundtrack has come out, you don't need us to help with that.”