The canvases of the V.J.'s can be far larger than the walls of a club. On its North American tour this year, the Canadian group Rush is performing with a video jockey, James Ellis, who is contributing custom animations in venues as large as Madison Square Garden.

Mr. Ellis says the content is a fine balance between improvisation and tight adherence to song structure. A team from a software company called Derivative spent two months creating special video loops and animations for 11 of the songs Rush performs on tour. The imagery includes original cartoon characters that bounce and stretch to the music and a time-lapse montage of still photos of the group's drummer, Neal Peart, on a motorcycle trip. Mr. Ellis then manipulates the video and animations in real time, creating an experience that falls somewhere "between the tight choreography of a film or musical, and the spontaneity of an improvisational jazz musician," he says.

Geddy Lee, the lead singer and bassist of Rush, says the band almost skipped video on the latest tour. "It's been very overused by pop acts," he said. "With the video culture of the last 20 years, there's too much explaining away of music." But the software can be used "in an interactive way, pulsing to the music, which was exactly what I had in mind," he added. "Bands all have the same instrumentation, but they all sound different. With video, you have to look at it the same way — it's how you employ it."

While many of the digital tools are new, the marriage of visual effects and rock music is, of course, almost as old as rock itself. Many V.J.'s trace their roots back to the late 1960's, when psychedelic light shows accompanied live music at halls like the Fillmore West in San Francisco or the Fillmore East in New York.... I used to love to run the lights when I DJ's clubs - a way to physically get inside the music, but this is a whole new league.