Tuesday, February 21, 2006


It is time for me to rave about Pandora.com. I first learned about Pandora in an article in the East Bay Express, one of several local alternative weeklies I tend to read over lunch. Pandora is a free website that streams digital music to your computer in a way that is fairly well tailored to your musical tastes.

How Pandora Works

The simple answer is that you type in a song or a band and out comes a succession of songs similar to the seed you provided. The exact methodology is known ony by those working at Pandora, and they're not telling everything. Nevertheless, they have revealed some of process.

They have apparently created a database of songs in which every song has been evaluated based upon a few hundred musical characteristics that they call "genes". I suspect that at least some of these genes are a set of binary flags indicating particular traits, and that some subsets of traits are mutually exclusive. That is, song might be considered to have the musical trait "major key tonality" or "minor key tonality" but not both at the same time.

(The application can provide a list of some of the traits used to select a particular song, and I believe I've seen "major key tonality" listed. I do not know if they lump all other tonal modes into a single category called "minor key tonality" or if they break them into seperate genes. Furthermore, I do not know how they handle cases of songs which change tonality.)

When you provide a song the application then selects a sequence of songs which are similar to that song. Pandora is not saying exactly how that selection is done, but it is possible to guess how it might work. I think that the algorithm randomly selects a set of traits for each song, and then having filtered based on those traits, it contructs a distance metric over at least some of the remaining traits and chooses a song which is within a specified radius using that metric. The radius selected is probably based on the number of songs which are considered close by the metric, so that is you're song is in a relatively sparsely populated part of the database the radius will be wider, and if the song is like a lot of other songs, the radius will be tighter.

I suspect that the initial selection of genes is not uniform distributed across all the available genes, and I'm not even certain that Pandora even reveals some of the genes that it considers important. For instance, I suspect that the release date of the track is a gene. I do not know that they even have to emphasize more recent releases over older material because I suspect the database is biased that way already. I suspect that the length of the track is a gene, as well. It would not surprise me if there were popularity genes based on sales or click-throughs to Amazon or iTunes.

When you listen to a song you may provide three forms of feedback. You may do nothing, you may give the song a thumbs-up (+), or you may give the song a thumbs-down (-). The most important of these appears to be the (-). If I understand the FAQ's correctly, a single (-) to a song will prevent that song from ever playing on that station. Two (-)'s on songs by one artist will prevent any other songs by that artist from playing on that station again. I suspect that (+)'s on the other other hand effect the distribution on the initial filtering genes. The more you (+) songs with a particular trait, the more that songs with that trait will be selected.

Why I Like Pandora

It's like having a comercial-free radio station that plays nothing but music that you like. I've never been a big fan of listening to music on the radio. My tastes just are far too broad and ecclectic to be found on any one station, or even on any one program on more adventuresome sources like college radio or public stations. One of my favorite memories was having the floor's scrounger come into my dorm room in college realize that I had a bunch of records that he could potentially borrow, having him examine my collection and watching his face fall as he realized that he recognized little if any of the records in my collection.

For me the most exciting thing about music is finding a new artist that I really like. Back in high school, someone at the local branch of a now defunct chain of record stores, Music Plus, used to put stickers with his or her comments on some of the albums. Those stickers led me to Novalis and Goblin. The first album I bought when I was in third grade was Carlos' Switched On Bach. The electronic music bin at Music Plus later led me to Synergy, Tangerine Dream and Vangelis. And so, of course, I came to more popular groups like Yes, Genesis, ELP, and Kraftwerk. Often I learned of bands before the became popular, and, I admit, I was sometimes disappointed when they did. (I still think that stance is somewhat justified when the hoi palloi acclaims the Human League's "Don't You Want Me Baby" when they were doing a bit more interesting stuff in the years prior to that release, for instance.)

I do like it on those rare occasions when I can turn people onto something they never would have heard otherwise. One New Year's Eve party at Leslie's old appartment, she asked me if I had anything to put on, and I tentatively put in the Hedningarna compilation released in the US as Fire by The Heathens. To my utter and complete surprise the entire room started dancing to it! Ladies and gentlemen we have a winner!

Pandora completely satisfies that need I have to explore for new material while still enjoying old favorites. I've never been that enthused by the MP3 exchange explosion and iPodery. First, there was the moral considerations of peer-to-peer copying. I want the artists I like to be compensated by my purchases. Second, I like to gain some context for an artist by hearing their music within the program defined by an album side or a cd. How would an iPod or iTunes help me find the next Hedningarna?

But the potential for Pandora's finding me groups like Hedningarna seems limitless. I have station already which streams me pop-punk, folk, techno-pop and reggae, and I love it! I already found some new bands to match my tastes, and will have to go on a cd buying mission to Berkeley here shortly (I want local record stores to stay in business).

It Could Be Better, Though

Because my house is a loft, my home computer is in the same room, essentially, as our home theater where my son spends his non-homework hours playing. And so, the first thing I did when I discovered Pandora was figure out how I could get a decent headphone system to work the Pandora stream coming through my computer. I swiftly leanred about the strange and wonderful world of Head-Fi which has grown up around portable audio. Thanks to the help folks at the Head-Fi forums I purchased a nice set of circumaural headphones (Beyerdynamic DT880's from Jan in Germany) and the second-to-last Go-Vibe v4 headamp ever produced by Norm. It's such a boutique business! It took me month to get all the equipment, but I am extremely satisfied with my set-up now.

I do, however, wish there were a way to carry Pandora with me. Right now, the Pandora application requires at least a Flash 7 player. Currently, the smallest devices with Flash 7 players are laptops which are all more than I want to carry. Adobe just released Flash Lite 2.0 which should be able to run Pandora on PDA's and cellphones, but it won't be until later this year for such devices to come available.

The second complaint that everyone has about Pandora is, of course, that the selection of music is limited. Right now, any music before the turn of the century is pretty spotty, many genres are sprasely covered and some genres like Classical in particular are not available at all. My personal preferences would put World Music on the top of the list for expansion, then probably Classical. More, broader, wider!

As for the application itself, I have some minor suggestions. I really wish that the three station edit tabs were sortable alphabetically by title and artist. In particular, the second (-) for an artist is a pretty big decision for a station, and so it would be nice to warn you when your about to do so. I wish there was a way to delete songs from your favorites page as well. When I create a station, I often want to be able to publish that station and so I just pick a song as a favorite on that station to get it posted to the favorites page.

Finally, I wish there was a message board community around Pandora to share stations and station building techniques and to talk about music and Pandora.

All in all, however, Pandora has been the best thing in music to enter my life in a long, long time. I am looking forward to discovering new music and enjoying old favorites through it. I hope that it remains free, but that the company achieves financial success. I look forward to seeing how the product will evolve. I think that Pandora will be an important part of my life, hopefully for years to come.

1 comment:

Tom Conrad said...

Thanks for the thoughtful post. We're hard at work on many of things you talk about as areas for improvement. Glad to have you as a listener,

CTO @ Pandora