How Pandora Radio Works

Pandora Radio is different from other Internet radio sites. Instead of relying on genre, user connections or ratings, it uses a Music Genome. Learn exactly how Pandora Radio works to create Internet radio stations.
Photo courtesy Pandora Media, Inc.

When it comes to finding new music for your library, there are a lot of ways you can go. You can spend hours combing Web sites for new artists and listening to clips. You can frequent music blogs or message boards. You can trust the Amazon-type "people who bought this also bought" recommendations or listen to radio stations and podcasts waiting to hear something new and appealing. You can scan the music libraries of friends who actually enjoy doing the music-finding legwork.

With the advent of Web-based "music-discovery services," though, the art of finding new music has changed. Internet radio sites like TagWorld, and Pandora let you type in a song or artist you like and instantly find other music that might fit your taste. But while Pandora provides a similar service to and TagWorld, it actually works very differently. Starting with the British band Gomez as the initial input, the first several "matches" from include the Doves, Badly Drawn Boy and Radiohead. TagWorld returns songs by R.E.M., Badly Drawn Boy and Radiohead. Pandora delivers Cheap Trick, Modest Mouse and The Vines. The difference is the Music Genome Project.


Pandora has no concept of genre, user connections or ratings. It doesn't care what other people who like Gomez also like. When you create a radio station on Pandora, it uses a pretty radical approach to delivering your personalized selections: Having analyzed the musical structures present in the songs you like, it plays other songs that possess similar musical traits.

­Pandora relies on a Music Genome that consists of 400 musical attributes covering the qualities of melody, harmony, rhythm, form, composition and lyrics. It's a project that began in January 2000 and took 30 experts in music theory five years to complete. The Genome is based on an intricate analysis by actual humans (about 20 to 30 minutes per four-minute song) of the music of 10,000 artists from the past 100 years. The analysis of new music continues every day since Pandora's online launch in August 2005. As of May 2006, the Genome's music library contains 400,000 analyzed songs from 20,000 contemporary artists. You won't find Latin or classical yet: Pandora is in the process of developing a specialized Latin music Genome and is still deep in thought about how to approach the world of classical composition.

When you arrive at, the first thing you see is the player, which is pretty sweet. It's Web-based (no download), minimalist and seamless. is our interface with the Music Genome Project database. All you do to get started is type a song or artist into the main field of the player. If we type in, say, "Ben Folds" and click the "create" button, we've created a radio station called "Ben Folds Radio" that will only play songs with similar musical traits to Ben Folds' songs.

In the next section, we'll look at how Pandora uses the musical traits of a song.



Musical Traits

And what are some of the musical traits of Ben Folds' songs? To let us know, Pandora chooses a Ben Folds song at random and plays it for us. In the bottom portion of the player, we can see how the Music Genome Project has characterized this particular song (see above). The next song the station plays will share some of those traits. In this case, it's "Amsterdam" by Coldplay.

Pandora automatically displays the Music Genome traits for the first couple of songs our new radio station plays. After that, we can find out exactly why Pandora is playing any song by clicking on the album art and choosing "Why did you play this song?" from the menu. After "Amsterdam," Pandora plays Ben Jelen's "Give It All Away." Let's find out why.


Clicking on the album art brings up a menu of options.
Pandora explains why it's playing "Give It All Away."

You probably notice in the above image that the trait description begins with "Based on what you've told us so far." It's not just talking about the fact that we like Ben Folds. Pandora wants us to give it feedback so it can refine the station based on our likes and dislikes. We can give any song the station plays either a thumbs-up or a thumbs-down, and providing this feedback instantly changes the station's playlist. Let's say we don't care for "Give It All Away." To give it a thumbs-down, we left-click on the album art and chose the thumbs-down, "I don't like it" option.

Now Pandora will never play "Give It All Away" on our Ben Folds Radio station again, and it will play songs that are genetically similar to "Give It All Away" less often. If we click on the arrow next to the Ben Folds Radio station and choose "Edit this station," we can see that Pandora has put "Give It All Away" on the list of songs we don't like.

We can edit any of these lists.

Giving a thumbs-up has the opposite effect -- that song and other songs like it will play more often. The idea is to continually provide feedback so the station learns more and more about what we like and don't like. The result is a progressively personalized radio station that really does play only music we want to hear. It takes a while to get there, but most people agree that the feedback process works. Some of the other things we can do with Pandora include:

  • Add more music to a station (based on a new seed song or artist)
  • Add a song to our Favorites list so we can keep track of the music we like
  • Buy the music we like from Amazon or iTunes by clicking on the album art and choosing a store
  • Share a station with a friend through an e-mail link
  • Minimize the player so it sits in the corner while we do other stuff on the computer
  • Create up to 100 stations
  • Register for RSS feeds to find out what your friends are listening to, what the top 20 artists are and other information
  • Link to Pandora stations from your blog (Pandora will even generate the code for you)

There's a lot going on with the Pandora player, but it's all pretty easy to access once you get the hang of where the clickables are. Next, we'll take a look at what's happening behind the scenes of the Pandora experience.


Behind the Scenes at Pandora

The Pandora player is a free, Web-based Flash application. You don't need to download anything to use it as long as you have Flash 7 or 8 installed on your computer. The only difference between the free service and the subscription service ($36 per year or $12 for three months) is the ads in the free version. Everything else is the same.

Pandora delivers a 128-Kbps stream of music, and it only works with a broadband connection. It derives its music license from the DMCA (Digital Millennium Copyright Act of 1998) guidelines for streaming Internet radio, and the digital rights management (DRM) scheme it employs is notable in a few ways. First, Pandora will never play a specific song on demand; if you add a song to a station, it will show up eventually, but Pandora can only work it in at random. Also, you can only skip 10 songs in an hour -- this is so you can't just skip to the song you're looking for. The license also limits the number of times Pandora can play a particular song or artist in a particular time period, and to this effect Pandora stores a list of the songs played on your station in your computer's Flash local storage so it knows what it has played already. It also stores your user data there so it recognizes you when you arrive at


Probably the most interesting stuff going on behind the scenes has to do with the Music Genome Project that Pandora taps into. Unless you've got a degree in music theory, most of the Genome's terms of analysis are outside the realm of common usage, but it's still cool to check out some of the parameters it's using to determine which songs are genetic matches for your seed song or artist.

The Music Genome is not a single, homogenous set of traits. Different types of music require some different subsets of genes. There are four basic groupings within the Genome: pop, jazz, rap/hip-hop/electronica and world. According to Music Genome Project founder Tim Westergren in a Tiny Mix Tapes interview:

... there is a common genome that crosses all genres. But ... World music for example, requires a much broader palette of different instruments than are used in pop music. It doesn't make sense to do all that work in pop music when it's redundant 99% of the time so we adapt the template to closer match what the demands really are for that genre of music. Rap, for example -- there's more detail around lyrics in the rap genome than there is in the pop genome because rap is so much more lyrically focused. We'd focus on the literary and delivery -- rhyme schemes, rhythm, and wording; like how much profanity there is.

Speaking of profanity, an interesting side note: Pandora only plays the explicit version of songs. The people at Pandora discussed it at length and decided to stay true to the artists' original intentions. When you register for Pandora, you need to provide your date of birth, and maybe that's part of the reason why.

In the next section, we'll take a look at how the Pandora playlist is assembled.


Assembling the Pandora Playlist

So here's what happened behind the scenes when we created our Ben Folds Radio station: Pandora located a song by Ben Folds and pulled up the Genome analysis for that song. It then ran an algorithm that compared every song in the Genome database to the genetic makeup of that song in order to identify songs that have similar traits. The algorithm looks for matches across 400 parameters. Here's just a handful of the traits and concepts it looks at (definitions excerpted from the Virginia Tech Multimedia Music Dictionary):

  • arrangement - the selection and adaptation of a composition or parts of a composition to instruments for which it was not originally designed
  • beat - the regular pulse of music
  • form - the structure of a composition, the frame upon which it is constructed; based upon repetition, contrast, and variation
  • harmony - the concordant (or consonant) combination of notes sounded simultaneously to produce chords
  • lyrics - the words of a song
  • melody - a succession of tones comprised of mode, rhythm, and pitches so arranged as to achieve musical shape
  • orchestration - the art of arranging a composition for performance by an instrumental ensemble
  • rhythm - the subdivision of a space of time into a defined, repeated pattern
  • syncopation - deliberate upsetting of the meter or pulse of a composition by means of a temporary shifting of the accent to a weak beat or an off-beat
  • tempo - the speed of the rhythm of a composition
  • vamping - to extemporize the accompaniment to a solo voice or instrument
  • voice - the production of sound from the vocal chords, often used in music; falls into six basic categories defined by pitch, ranging, from bottom to top, Bass, Baritone, Tenor, Contralto, Mezzo Soprano, and Soprano

Keep in mind here that every song's traits are determined "by hand." There was an actual human being who identified the characteristic voice types, beats, structures and tempos for each of the 400,000 songs in the Genome database. It's a profound undertaking that will probably continue for as long as Pandora Media has the money to pay its experts to listen to music all day.


We'll take a look at some concerns with Pandora in the next section.


Pandora Concerns

There are, of course, concerns about the Music Genome Project from some in the music world. First, since the Genome is proprietary, there's no possibility for independent review. For all we know, Pandora Media's "experts" don't know the difference between syncopation and vamping. Also, in a much broader way, the Music Genome Project assumes that music's traits can be objectively analyzed at all -- that the mind of the listener can be left out of the equation. Some experts doubt that music can be quantified in this way.

Regarding the player itself, an issue arises when you create a station using an artist like The Beatles as the seed. Some artists have such a varied collection of styles that there are endless ways the Genome algorithm can go when determining matches. In such a case, Pandora may return music you don't like at all. For instance, if you love the Beatles' later stuff like "Across the Universe" or "I am the Walrus," you'll probably be disappointed if Pandora returns music that's similar to "I Want to Hold Your Hand." For this reason, it's often wise to use a song instead of an artist as a seed.


With all of Pandora's attractive features and novel approaches to personalized radio, it does tend to wow people when they discover it. But wows don't pay the bills, and Pandora will have to bring in real cash if it's going to survive. In the next section, we'll find out how Pandora plans to turn the academic Music Genome Project into a commercial commodity.

Pandora's Future

Slim Devices' Squeezebox
Photo courtesy Pandora Media, Inc.

The Music Genome Project and its accompanying user interface are not exactly the first of their kind. Music producer Alan Lomax, best known for his work in the 1950s and '60s with BBC radio and folk artists like Woodie Guthrie, Lead Belly and Pete Seeger, spent 30 years developing an interactive music and dance "jukebox." Lomax's Global Jukebox makes social, cultural, historical and regional connections between various art forms. The connections are based on a Genome-like analysis of musical traits and dance moves combined with a database of cultural characteristics throughout history. According to's Martin Edlund in "The Madonna Code," the Global Jukebox can tell you that "a high-energy vocal style correlates with the presence of dairy in a society's diet." In "Alan Lomax's Multimedia Dream," Michael Naimark reports the connection between "dances with narrow heel-to-toe movements" and "societies whose main crop is planted in narrow rows (like rice)." The Global Jukebox prototype is currently stored on an Apple Quadra in New York City's Lomax Archive. Many corporations expressed great interest in the creation, but none followed up with a commercially viable use for it.

So how does Pandora plan to turn academic analysis into cash? Approaching the question from a theoretical standpoint, Pandora's potential commercial success is based on an economic concept called the "Long Tail." In the digital age, where consumers can easily find the specific thing they're looking for and producers can easily provide new content for distribution, Long Tail states that directing consumers off the beaten path is a potential key to profitability. In practical terms, Pandora's current revenue model seems to involve placing advertising in the free version (no ads in there as of May 2006), charging subscription fees for the ad-free version (as of May 2006, about 15 percent of subscription revenue goes to maintaining Pandora's music license and buying bandwidth) and sending users to iTunes and Amazon to buy the music they hear on Pandora. Pandora Media also licenses a commercial version of the music-discovery service to music sellers like Best Buy, Tower Records and AOL, who use it to recommend new music to their consumers at kiosks. According to the Pandora FAQ, what the company won't do is sell their objectivity. In the company's words, "We will never, ever take money to play a song or analyze it favorably on Pandora." So selling airtime is probably out.


If Pandora is going to be a real commercial success, it will have to compete with music giants like iTunes. Pandora already has teamed up with an electronics company to create a piece of hardware that releases Pandora from your computer, similar to what Apple's AirTunes does with iTunes. The Slim Devices Squeezebox plugs into a home network to stream Pandora from your computer and control it from anywhere in your home. And Pandora Media is already talking about taking Pandora mobile in the form of a standalone player and an application for devices like cell phones and PDAs. Gift subscriptions are in the works, and as soon as Pandora can work out the international licensing agreements, the service will be available outside the United States.

For more information on Pandora and related topics, check out the links on the next page.


Lots More Information

Related HowStuffWorks Articles
More Great Links

  • "Does Music Have a Genome?" DJ Alchemi. Nov. 28, 2005.
  • Edlund, Martin. "The Madonna Code."
  • Farber, Dan. "Tapping into Pandora's music genome." ZDNet Blogs. Aug. 26, 2005.
  • "Frequently Asked Questions."
  • Ike, Elephant. "Tim Westergren Interview." Tiny Mix Tapes, Jan. 2006.
  • "The Music Genome Project."
  • "The Music Genome Project."
  • Naimark, Michael. "Alan Lomax's Multimedia Dream." The Alan Lomax Collection.
  • "Pandora, the Music Genome Project." Mariva's Guide. Jan. 23, 2006.
  • "Powered by the Music Genome Project, New Pandora Service Makes It Dramatically Easier to Find and Enjoy New Music." Business Wire. Aug. 29, 2005.
  • Westergren, Tim. "The Music Genome Project." AlwaysOn. June 2, 2005.