Multi-instrumentalist Jim O'Rourke left Sonic Youth after 2004's Sonic Nurse, and because the stripped-back, streamlined performances on the band's latest, Rather Ripped (Geffen), have a liberated eagerness that's at odds with his penchant for elaborate arrangements and just-so studio treatments, it's tempting to attribute the album's sound to his departure. But even a half-awake listen to Sonic Nurse makes it clear the band was already headed this way, and in a recent Wire interview singer-guitarist Thurston Moore suggested a more credible reason for the current direction: his immersion in the international free-improv underground gives him so many other places to make noise that he doesn't need to bring any to Sonic Youth. Rather Ripped's songs are lean and succinct, with nary a wasted gesture. On "Reena," the opening track, Kim Gordon's lyrics about a scenester's breakdown read like a series of bullet points, and the guitars stick close to the hook instead of peeling off into their trademark chaotic extrapolations. And the Moore-fronted "Sleepin Around" quickly abandons an initial feedback eruption to achieve escape velocity with a hurtling Velvetsy groove. Sonic Youth performs on the second day of Lollapalooza; for a complete schedule see page 42. At 11 PM the band plays a free afterfest show with Feist at Double Door, but tickets must be won through WXRT; visit wxrt.com for details. Sat 8/5, 4:30 PM, Bud Light Stage, Lollapalooza, Grant Park, Columbus & Congress, 866-915-6552, $65 for a one-day pass, $150 for a three-day pass. All ages.