Jazz is all about restraint, even when it doesn't seem like it. Look at free jazz for instance. Where's the restraint? In free jazz, anything goes, tonally, rhythmically, even timbrally. But the energy at the center of the music, the flow that musicians try to find and articulate, requires restraint, as paradoxical as that may seem. That's why a nonmusician playing a free passage sounds different from a musician playing a free passage. Free jazz lets go of the traditional vocabulary of music but not of the power of what is said explicitly and what is only implied. In other forms of jazz, restraint is easier to pick out. The beauty of a ballad is often the note or chord that is approached again and again but never actually played.

Rock music is different, though. There are limitations of form and structure, but the point of rock music is usually to find a theme and pound on it until it's obliterated. That method of tapping into music's primal energy is the reason that much of the best rock music is made by beginners on their instruments. Subtlety is not a prerequisite; restraint is for sissies. So what, then, to make of a jazz show that feels decidedly like a rock show?

At Williamsburg's North Six, the stage is elevated, the bass drum and the stack of bass speakers lined up evenly with most of the audience's ears. Giant speakers hang from steel columns in front of the stage. So when Tim Dahl of The HUB announced the band's lineup on a recent Saturday night, and booed his own name and banged on the strings of his bass which fed through a distortion box into his maxed out amp, a mixed audience of North Six regulars and local jazz heads began to sense that this would not be an evening of moderation.

The HUB is an alto sax (Dan Magay), bass (Tim Dahl) and drums (Sean Noonan) trio, but its music is so aggressive that any comparison to similar lineups would be naive. Songs start out with themes and then vary not withharmonic substitution or counterpoint, but with cacophony. Sections fly by quickly and can often bear no resemblance to what came before. There's a lot of banging and squealing.

The musicians have talent, and lots of it, but the music calls for an abandon that defies that talent. Dahl, in particular, plays like he resents his own technique. He'll start a complex solo, with lots of notes and harmonics, and then pull violently at his strings, bang on the bridge and smack the song into a new section. But as the band has developed, he's begun to play less of the complexity and more of the clamor. On its latest CD, Trucker, the trio finds its sound developing even more of a rock aesthetic than its previous ventures. The band has pounded through its themes over the past several months, and unnecessary elaboration has begun to fall by the wayside.

Following The HUB was the Young Philadelphians, a group consisting of Marc Ribot on guitar, Jamaladeen Tacuma on bass and Calvin Weston on drums. This group played with a similar loudness, though its bluesy grooves were far more consistent than The HUB's ADHD-influenced flights of frustration. But the main difference between the groups was in their drummers. The HUB's Sean Noonan defied restraint with ever-shifting rhythms, a new idea on every beat, whereas Calvin Weston played powerfully through the basic themes of the tunes. Weston left virtually nothing unsaid, picking up each bit of energy that Ribot and Tacuma summoned through their strings and pounding all over it with his kit. Most of the audience walked outside at the end of the night with ringing in their ears and stomachs full of beer.

That six jazz musicians could play through a whole show with barely a thread of self-control begs the question of how useful their talent is to the sound they're going for. After all, rock music doesn't ask that you learn scales or arpeggios, only that you be prepared to jump on in. What makes these guys different from any other rockers? It may be too early to tell, with each group still developing. But one thing is for sure. The music isn't boring