The Mars Volta, led by vocalist Cedric Bixler and guitarist Omar Rodriguez, formerly of the El Paso-based postpunk band At the Drive-In, forfeited much of their considerable mystique when they finally released their first album, "Deloused in the Comatorium," last summer. Until then, their reputation was based on concerts that had critics comparing them to everyone from King Crimson to Fela Kuti.

The album was, perhaps inevitably, a letdown, since Mars Volta's manic progressive rock can sound pretentious on record. It was difficult to see what all the buzz was about, but then a letdown implies expectations that aren't met, and if anything characterizes the career of Bixler and Rodriguez it's their refusal to fit anyone's preconceptions.

Even if you've seen them perform before, there's always the shock of the new when the band comes on. At August's Summer Sonic festival, they took the stage with spacey keyboard-guitar noodling that expanded outward and eventually exploded as the band came together in what can only be described as an At the Drive-In moment: Omar stumbling backward, Cedric diving head first toward the audience, and the band locking into a punishing, incoherent roar. For 60 minutes they lurched and changed gears without warning, alternating soaring jazz fusion freak-outs with head-banging hardcore as Cedric threw his skinny, Afro-topped body around and over things, including other musicians. Pretension it was not. It was total immersion.