Thursday, January 15, 2009

How does iTunes Genius work?

I've been using iTunes Genius lately to make playlists and I've been really happy with the results but this morning something amazing happened - I chose a Postal Service song to start the playlist and iTunes picked the only two covers of Postal Service songs I have on my computer to put in the playlist - "Such Great Heights" by Iron and Wine and "We Will Become Sillouettes" by the Shins.

So, how did it know to pick those? This isn't just genre matching - there is more going on that that. When I start with a solo Beatle it gives me other solo Beatles. When I give it Stevie Wonder it gives me other artists that match quite well. I'd love to know the algorithm it uses to come up with the lists.

Any ideas?

12 comments:

bethany said...

I thought they started with the "people who bought this also bought" database.

Bob K said...

Bethany - that might be a place to start but I've bought lots of different types of music and I imagine most people have. I'm not sure how that would help.

To make things more challenging, in a mix started with a country song it included a country-flavored Bruce Hornsby tune!

Keymo said...

Those Postal Service covers are both on the Such Great Heights EP. So it is obvious to iTunes that those songs go together as they are included on an album whose album artist is the Postal Service.

Bethany is correct, it works on the "people who bought this also bought" database, which is extensive.

Sometimes it works pretty well, but it is still very dependent on you having the music available to choose from (obviously). What I don't like about it is that it will choose more popular artists/tracks (even within respective genres) over music that might sound good together. Because it has no idea what sounds good together (that's for amateur mixers such as myself to do).

Keymo said...

HOWEVER, I have no idea how it can genius playlist the Beatles. I just did a genius Beatles playlist on my work computer and it made a sort of indie rock supermix. Probably because all the music on my work computer is really awesome indie rock.

Bob K said...

Keymo - the Iron and Wine song was from the Garden State Soundtrack so it's not *quite* so obvious. I think there is more to it than that because it got better since it first came out.

Justy said...

http://itunes.apple.com/WebObjects/MZStore.woa/wa/viewAlbum?id=20922902&s=143441

This is a link to the Such Great Heights EP where you will find the Iron & Wine cover of Such Great Heights, which was also found on the Garden State ST. iTunes puts more stock in Name/Artist than Album.

Also, thousands of people discovered PS via Garden State, so there is a connection in people who bought that album and the people who later bought Give Up.

Bob K said...

Keymo (Justin) - yes, there is clearly a connection between Garden State and PS but that's my point - it's not obvious to the casual observer or casual computer for that matter. I think the Genius algorithm is more complex than you've suggested.

bethany said...

I think the "also bought" algorithm works better than you believe. Think about how uncanny amazon suggestions often are. While it is true that individual people have a wide variety of music, it is also true that certain things co-appear more than others.

Isorski said...

It may also involve the metadata that each song is tagged with. Who wrote it, who was the producer, what year it came out, etc. And of course the genre. I started using Genius as well and it does put together very cool lists.

Lucas said...

I too used to like the way Genius puts together playlists. After using it for a while quite often though, I start noticing something which in turn started annoying me. Genius uses `popular' songs (by which I mean those songs from albums that were released as singles, used in commercials, etc.) way more often than other tracks.

This means that if you choose a song in a certain `genre', say Indie Rock, the playlist always turns out pretty much the same, regardless of which song or which band you picked to start with.

I started using the Genius playlist feature to, so to speak, rediscover my pretty big music library. If it serves me the same songs over and over again, this kind of defeats my purpose.

Any thoughts?

Bob K said...

Lucas - I'm totally guessing here but I think iTunes Genius works a bit on what other people have in their collections too - so it makes sense that the most popular songs are going to show up in other collections more often than the less popular ones.

That said, I haven't used it often enough to notice what you did ... yet.

Thanks for your comment!

Preston said...

This website I looked at had a very detailed explanation as to how Genius Works. http://www.line-of-reasoning.com/issues/how-does-apple-genius-work/