Lord knows the Chicago improv scene is teeming with casually convened groups, assembled for the purpose of exploring fleeting dynamics and textures, but here’s one that’s made a document of its findings. On Pillow’s eponymously titled debut, bassist Liz Payne and guitarist Ben Vida (who both play in the down-home minimalist band Town and Country), cellist Fred Lonberg-Holm, and reedist Michael Colligan carefully blend and contrast gently articulated sounds, many of which are tough to identify: strings are plucked, scraped, and bowed, while Colligan manipulates his clarinet to sound like anything but; yawning legatos are punctured by thorny barrages of notes, metallic patters are layered with screeching harmonics, and subtle hisses are blown away by violent cello thwacks. The nature of improv, of course, is such that Pillow might do something completely different live, despite the fact that this is billed as a record-release party–but even if they do they’ll probably pull it off with the same aplomb. Wednesday, 9:30 PM, Empty Bottle, 1035 N. Western; 773-276-3600. PETER MARGASAK