What is the sound of one band playing? It is loud, first of all, around 120 decibels. How is it powered? By AC/DC, of course. "Let There Be Rock," a 2-year-old concert film of what has become the world's most popular heavy-metal band, is screening through Thursday at the Uptown Theater. It captures the band on its way to the top even as one of its members heads to the bottom.

"Let There Be Rock's" continuing interest comes less from the music--a metallic k.o. which begs either total acceptance or total rejection--than from its sketches of diminutive lead guitarist Angus Young and singer Bon Scott. At one point an interviewer asks Scott why the other band members regard him as "special." Looking a bit embarrassed, he replies, "I'm a special drunkard. I drink too much . . . I see stars sometimes." In March 1980, several months after the film's completion, Scott died from alcohol poisoning.

Watching him perform and answer a few inane questions, one senses an immensely likable grunt, a one-time chauffeur for rock 'n' roll stars who suddenly found himself in the back seat and in the money. It was a turn-around world in which Scott wore good clothes offstage but appeared on stage in battered jeans with deliberate fault lines ripped as if his erogenous zones needed air. Scott was a fine singer, his Howitzer voice just right for rock's amplified warfare. He was a compelling performer as well, often standing slightly askew as if shock waves of sound were buffeting him around the stage; eventually they blew him right off.

Despite his knickered schoolboy outfit, Angus Young is the quintessential metallurgist. Even in the massive wash of AC/DC's sound, his stinging, fluid and inventive blues-tinged guitar lines come across with searing power. Young is also a frenetic performer who often looks as if he's stepped into an electrified puddle.

"Let There Be Rock," filmed in Paris and Brussels in 1979 and early 1980, offers few insights into the workings of the band, but then its aim is as true as it is low. Mercifully avoiding superfluous crowd shots, directors Eric Dionysius and Eric Mistler have come up with some distinctive camera angles. Most of the film is shot high on the lip of the stage (only a foot or two from the band) or from a high moving dolly that provides a new performance perspective--rock from the top. The close-up cameras linger mostly on Scott and Young as the band runs through its repertoire of the time including "Hell Ain't So Bad," "Bad Boy Boogie," "High Voltage," "Sin City," "Girl Got Rhythm" and "Highway to Hell." There is nothing pretentious about AC/DC's awesome energy; it aims for the gut and reaches it through the ears. Loud it is, bad it's not. In fact, with its bank of speakers, the Uptown's concert is almost as loud as it would be if performed at the Capital Centre. And for fun, you can join the French audience singing the chorus to "She's Got the Jack": "She Gut Zeee Jacques." Jazz is apparently not the only music that is universal.