For music fanatics, casual listeners and curious minds, the customizable online radio at Pandora.com ought to be of serious interest.

The website bills itself as a music discovery service - type in the name of a favorite artist or song and the site will find other choices to match your taste. It has already changed the way at least 3.5 million users discover and enjoy music, and its reach seems to be expanding, in part due to cooperation from industry giants but mostly because of those who use the free service.

Pandora co-founder and lifelong musician Tim Westergren has spearheaded a promotional campaign, traveling all over the nation to connect with users through town-hall meetings and open forums. He will host a forum tonight at 8 p.m. in the Student Activities Building's Maize and Blue Auditorium.

Pandora has come a long way from its rough beginnings. For nearly two years, employees of the fledgling company labored relentlessly without salary, fighting to bring it to the surface at the tail end of the dot-com bust. What could possibly compel a staff to follow something so impractical? What values must these people have had that they were willing to forgo compensation (necessity ultimately forced many to quit), and to what end were their toils directed? The answer, quite simply, is the music.

Music has been a constant force in Westergren's life. He began playing piano at 7. Though his time is now almost completely consumed by Pandora, Westergren continues to play piano at least once or twice a week. After studying computer acoustics and recording technology at Stanford, where he received his bachelor's degree, Westergren spent the next decade playing in rock bands, the five years after that working as a film composer and additional time as the owner and operator of commercial digital recording studio Nightfly Studios.

Westergren said he undertook the projects that led Pandora (and its foundation, the Music Genome Project) because music was such a personal part of his life.

"In my life, music and music discovery is one of the things that affects me the most emotionally," Westergren said. "If I was to really boil down this whole adventure, this whole company, into its most basic inspiration, it's the feeling that I get when I find a new band or a new song that I like. I think that that is one of the great things in life, and so I wanted to spread that feeling."

He also wanted to build a business for profit, he said, but added that "what makes a business last and makes a business maintain a sense of purpose and coherence is some kind of core to it that has to come from you naturally."

Westergren's motive for traveling cross-country to talk about Pandora is that it allows him to connect with the people who use the service. Westergren emphasized that the meetings provide not only insight but inspiration - something hard to come by when most of your time is spent behind cubicle walls.

"We meet thousands of really really fanatical music lovers," Westergren said. "And in some way it makes real what we're trying to do. It gives us a chance to see how it's impacting people, and how important music is to people. It's really energizing."

Westergren and the rest of the Pandora team have a considerable agenda. Among other things, they plan to discover unknown artists and streamline the discovery of new music.

Pandora is above all a promotional service. It helps users discover new music they are likely to enjoy by giving users the freedom to design their own radio stations based on songs or artists of their choosing and then matching those choices with similar-sounding songs.

Westergren's Music Genome Project is at the core of the process. The project identifies 400 "genes," including "chromatic harmonic structure," "blues influences," "extensive vamping" and "rhythm syncopation." Every song is evaluated based on the presence, absence, degree or manifestation of each gene.

Pandora also employs a staff whose full-time job is to listen to and analyze every new song that comes into the database. The process generally takes 20 to 30 minutes, and the website adds 15,000 songs every month.

Finally, a user selects a station, and Pandora uses an algorithm to match songs according to their "genetic" similarities and streams them live.

At any point during the stream, the user may provide feedback in the form of a "thumbs up," which tells the algorithm to play more songs like this, or a "thumbs down," which signals the program to avoid similar songs. Users are encouraged to submit comments, complaints and requests for missing music directly to the Pandora team via e-mail. "Our core policy is to respond individually to each e-mail," Westergren said.

But Pandora certainly has its shortcomings, like its limited scope and availability.