German guitarist Annette Krebs doesn’t play chords, lines, or riffs when she improvises. In fact, her guitar makes none of the noises you’d expect from that instrument. As with an ever increasing number of improvisers who use their axes as pure sound generators, Krebs makes miniature aural gestures, delicate shapes that disappear almost as quickly as they emerge. Using electronic processing and a variety of contact mikes, which she arranges on different parts of the guitar to amplify physical actions instead of string vibrations, Krebs paints wonderfully alien squiggles, swooshes, and splatters. She pays no heed to melody or harmony, and her pieces never really resolve–they just start and then, eventually, they just end. Rotophormen (Charhizma, 2000), recorded with electronics manipulator and prepared-piano player Andrea Neumann, is metallic yet gentle: muffled clanging, milky hissing, brittle scraping, and resonant pinging drift in and out, sometimes cutting off abruptly, sometimes decaying into the ether. Even when joined by a group of like-minded players–including trumpeter Axel Dörner, tuba player Robin Hayward, and saxophonist Alessandro Bosetti, on last year’s Phosphor (Potlatch)–Krebs performs with an identifiable delicacy. On her most recent effort, Guitar (A Bruit Secret), a three-inch solo CD, judicious panning heightens the effects of her decontextualized sounds, from floor-rumbling hums to what sounds like the hushed crumpling of paper. Krebs is touring with Brooklyn guitarist Chris Forsyth and San Francisco multi-instrumentalist Ernesto Diaz-Infante, whose recent duo album March (Pax) seems to borrow many ideas from Krebs, as well as from the early work of Chicago’s Kevin Drumm. Their interactions create some exciting moments of microscopic detail, but they occasionally fall back on the tired plink-plonk tricks of traditional free improv. The show starts earlier than the usual Wednesday night concerts. Wednesday, October 16, 8 PM, Empty Bottle, 1035 N. Western; 773-276-3600.