Photos: Listening in on Pandora

Pandora is deceptively simple. For free, members can create any number of radio stations based on the sounds of a favorite song or artist, such as "Blackbird" by the Beatles or just the music of Prince. Once the artist or song is found in the system, the station streams from the Web, within seconds, music that is rhythmically or artistically similar. Because of licensing restrictions, Pandora does not play any one song on demand. People can give a newly played song a "thumbs up" or "thumbs down" to tailor future selections, or they can request a new song or artist to add diversity.

The Music Genome Project, founded by Tim Westergren in 2000, is the basis for Pandora's music engine. The goal of the project is to codify as many as 400 different attributes of a song, such as composition and bass line and rhythm, and then catalog that music and musician so people can find the "musical neighbors" of any song, whether it's Latin, jazz, country, rock or gospel.

Westergren, founder of Pandora, a 7-month-old music-discovery engine. Westergren travels from town to town, sharing his time and story with fans who, because of his service, say they've rediscovered a love of newfound music.

An audience of about 200 people in San Francisco listened to Westergren and asked questions of him for about two hours on Wednesday night. Most attendees were fans of Pandora, but some people were musicians or from local indie record labels inquiring about how to get on the service. The event was the latest of about 25 town hall meetings and get-togethers Westergren has held since February.

Westergren plans to take to the road again this fall, meeting with college students at the University of Michigan, among other campuses. He has come a long way since February, when he met two people at a bar in Portland, Ore., and was stood up entirely in a bar in San Antonio, Texas.