Free improv can be as sloppy as punk rock, and Good for Cows goes for it, opting for aggression over precision every time. Neither bassist Devin Hoff (left) nor drummer Ches Smith has to prove his chops; witness Hoff's delicate interaction with the Nels Cline Singers or Smith's fast and furious precision with Trevor Dunn's Trio Convulsant. Instead, they just set out to prove how much noise an untethered rhythm section can generate, egging each other on with a lo-fi looseness that's part grin, part sneer. Smith's earthquake-inducing rumbles are met by Hoff, his strings smacking against wood so hard that they probably leave a mark. Hoff's bowed bass sounds like he's trying to saw straight through the strings, while Smith annoys neighborhood pets with the scrapes and screeches he elicits from his kit. Subtle as a blow to the head, but for the most part a lot prettier.

Thu., April 6, 8 p.m., $10, with Dijkstra/Hollenbeck Duo and Kuru Kuru Pa, Avant Gentlemen's Club, 4028 Filbert St., www.arsnovaworkshop.com.