Califone, Bush Hall, London

In a previous incarnation, Califone's core were once on the grunge label SubPop. The songwriter Tim Rutili has suggested they now play an update of their home town Chicago's blues. Listen to records like the recent Heron King Blues, and you may hear a third version of the band - a kind of narcotic folk-rock, with a structure prone to free jazz explosion. Whatever your preconceptions, nothing will prepare you for the inventive fun of seeing Califone live.

They look like four unassuming students, and when they start to play, the shift in gears from tuning-up is almost imperceptible. The first thing I notice is how unusually hard it is to decide where each sound is coming from, or what it might be, on a stage that is a more intricate, alive place than usual. It takes five minutes of the opening "Trick Bird" for me to fathom that one whining noise is slowly stretched, fading notes from a guitar, and by then a seagull screech is being sawed from its strings. A massive, brazen rock climax eventually rears up, then settles down to the barely amped striking of a guitar. As this extraordinary start softens back to silence, Califone look innocently non-plussed, as if they had nothing to do with it.

Somewhere in every song, you can hear that Tim Rutili is a fan of Seventies rock. But the bare bones of a traditional rock band have been built on by sedimentary layers of inquisitive imagination, more akin to rap producers like The Neptunes.

Califone, though, led by the computerphobic Rutili, use no complex technology. Instead, amplification and distortion do much of the work; playing just a banjo and acoustic guitar, they switch from alt.folk minstrels to free jazz freak-out at one savage twist of a dial. And then, there are the piles of instruments at their sides, ingredients they regularly reach for to keep their sound unstable. Though they stay a four-piece rock band, those pieces have been abused: the banjo's back and microphone's head have both been torn off. And why, you might well ask, is percussion king Ben Massarella hitting a wood-block with seaweed?

The hip young audience listen with keen pleasure, and demonstrations of cutesy devotion - like the girl who hands Rutili an Easter egg. There is no chin-stroking, just simple enjoyment of seeing music made with such inventive, naked physicality. Perhaps this tangible, visible element explains why Califone sound patchier on record. "Horoscopic.Amputation.Honey" anyway sees them sign off with a huge guitar blast. Califone's like a proper rock band, at last. Except for the tin cup drum. And the seaweed...