Although most of the sounds Francisco Lopez uses in his work are original field recordings, made in far-flung locales from Costa Rica to China, his music is determinedly abstract. Lopez insists that there's no deeper meaning in the sounds, and to prove it lately he's been releasing CDs in clear jewel cases without any contextual information--no titles, no credits, no artwork. That doesn't mean he doesn't expect listeners to pay rapt attention: his performances take place in total darkness, and if that's not possible he distributes blindfolds to the audience to eliminate visual distractions. And really, considering how imperceptible a piece like the recent Untitled #91 (Edition...) would be to a casual listener--swaths of silence interrupted by a multifaceted drone that seems to be rolling in from miles away--anything less than total immersion would be pointless. (This use of silence has nothing to do with Cagean notions of the musicality of incidental sounds. Lopez wants you to concentrate on how much there is in what little is there, not on the breathing of the person next to you.) Untitled #92 (Mego) is rather demanding as well. It's a 12-inch record of loops of crackling vinyl, and you're supposed to play four copies on four turntables at once, to cause the loops to mingle in different combinations. But careful listening is richly rewarded. On one older piece, Belle Confusion 969 (Sonoris), Lopez electronically transmogrifies recordings made in the rain forests of South America, Africa, and Asia into a shifting, striated swirl of sound that peaks in loud, near industrial blasts. An examination of the brush strokes that make up this aural painting opens up worlds within worlds. This is Lopez's Chicago debut. Saturday, 10 PM, 6Odum, 2116 W. Chicago; 312-666-4412 or 773-227-3617.