You know you are in for a challenging listen when a band's most melodic moment comes with a cover version of one of Yoko Ono's early 1970s howling marathons. And so it is with Erase Errata, a quartet from California who inhabit the more demanding end of the punk-funk spectrum, which means their songs accurately replicate the experience of standing at the bottom of a deep stairwell while someone at the top throws instruments down it. Theirs is the kind of performance where, when lead singer Jenny Hoyston whips out a trumpet, some of the audience visibly wince before she even plays a note.

None of this is to suggest that Erase Errata are not good - at full pelt, their jagged racket is fantastically exhilarating - just that they would work best in short, shocking doses. They play for the best part of an hour, which even they seem to realise is laying it on a bit thick. "We're going to play a couple more songs, then it's time for Le Tigre," says Hoyston, apologetically.

Le Tigre are challenging in a different way. Famed as rock's premiere exponents of radical feminism, the trio bound onstage in matching outfits and perform not the expected paean to sisterly power, but a squeaky cover of The Pointer Sisters' I'm So Excited. It's an indication of the remarkable balancing act Le Tigre pull off. Armed with songs about sexism, paedophilia and lesbian strength, Le Tigre may well be the worthiest band in the world, but they never seem like it. Oddly, the gig's muddy sound demonstrates why. You can't make out the lyrics, so you are forced to concentrate on the music in which the trio couch their messages. They sound like a 1960s girl group transported into the 21st century and fronted by Siouxsie Sioux: punchy drum loops and techno samples, overlaid with hooky buzzsaw guitar riffs and call-and-response choruses. Radical feminism has rarely seemed so much fun.

· Le Tigre and Erase Errata play the London Astoria tonight. Box office: 020-7344 0044.