Dutch trios Kapotte Muziek and Goem have identical lineups--Frans de Waard, Peter Duimelinks, and Roel Meelkop--and both groups use the same basic MO, beginning with a single sound source and processing it heavily. All the same, there's no mistaking one band for the other: the end results are strikingly different. De Waard started Kapotte Muziek--the name translates as "broken music"--back in 1984 as a solo project, exploring a primitive sort of musique concrete he calls "sound recycling." In the studio, the band is still just de Waard, but Duimelinks and Meelkop, both former members of the musique concrete quintet THU20, have been part of Kapotte Muziek's live shows since 1993. The group often uses simple objects as its sound sources; de Waard and Meelkop might scrape or tap on a few stones, for instance, while Duimelinks electronically treats the amplified noises. The few improvisations I've heard are abstract, shapeless, and monochromatic, but within these constraints there's a surprising richness of detail. I'm more familiar with the work de Waard and company have done as Goem, a project that started in 1996 when Meelkop found an electronic device called a "student stimulator" in a thrift store. Basically a variable-speed pulse generator, the machine is the core of Goem's purely electronic, loop-based music. The group's recent Abri (12k) is techno at its most minimal: ultrasimple beeps and beats, processed by various filters and effects, repeat endlessly, sometimes bathed in milky atmospherics and sometimes warped by lopsided accents. There isn't much in the way of dramatic development in this music, but taken on its own terms, its subtle wash of slowly shifting sonic minutiae can be surprisingly dynamic and powerful. A brand-new compilation called April, released by the local Boxmedia label, includes some Goem remixes, a serene Kapotte Muziek track, and solo pieces by Meelkop and de Waard, all of which work together almost as a suite, united by the artists' patience and attention to detail. Kapotte Muziek will perform on Friday and Goem will make its Chicago debut on Saturday; both sets will be broken up with solo performances by de Waard and Meelkop. Friday and Saturday, April 19 and 20, 10 PM, 6Odum, 2116 W. Chicago; 312-666-0795 or 773-227-3617.