The four members of the international quartet Poire_Z–Swiss percussionist and electronicist GŸnter MŸller, French turntablist Erik M, and the German duo of Andy Guhl and Norbert Mšslang, better known as Voice Crack–have spent years developing highly personalized approaches to sound. So it’s a testament to their improvising skills that on the group’s debut album, Poire_Z (on MŸller’s For 4 Ears label), their methods meld so seamlessly–in fact, it’s pretty much impossible to determine who’s doing what. There are admittedly a lot of sounds, including cold machine hums, warm static hisses, high frequency shrieks, distorted dropouts, siren whoops, underwater thwacks, hollow clicks, undulating synthetic tones, stop-start turntable whooshes, and abrasive sawing. But a mere list of them can’t really begin to cover what Poire_Z actually sounds like. The mood of the music drifts from tranquil to perturbed, but the polarities don’t seem extreme; more often than not the two ends of the spectrum overlap. Each of the album’s six pieces is amorphous but not haphazard, twisting, growing, and flowing according to a logic that evolves right along with the music. Some writers have called what Poire_Z does electroacoustic improvisation, but that term brings to mind an academic stiffness that’s absent from these beautiful soundscapes. Rarely does spontaneous music making sound so simultaneously ethereal and mechanical. This is the group’s Chicago debut. Wednesday, May 16, 10 PM, Empty Bottle, 1035 N. Western; 773-276-3600.