During Fred Frith's set at the 9:30 club Sunday night he kept his audience genuinely off-balance with one marvelous, uproarious surprise after another. Accompanied by a musician who alternated between cello, electric bass and a rhythm machine, he tore through a set of startling, raucous, remarkably accessible improvisations.

Frith roved a stage strewn with wires and electronic gizmos, stooping every now and then to trade his guitar for a violin -- which he played with a surprisingly lyrical touch, heavily flavored with traditional folk and Eastern motifs -- and then that for drums, and so on. He even sang a few bars.

The more focused segments of his performance were reminiscent of the recent work of King Crimson, which in fact is indebted to Frith's groundbreaking '70s band, Henry Cow.

Repetition can be used to cover up a multitude of sins. That's what the opening act, France's Etron Fou Leloublan, probably figured. They tried to cover up a paucity of ideas and shallowness of concept by repeating the ones they did have ad nauseum. Bass player Ferdinand Richard and the keyboard player hammered out a series of circular riffs while drummer Guigou Chenevier and Francis Grand on sax had at their respective instruments with much gusto and the least amount of imagination possible. There was not one surprising moment in their entire overlong set.