I've written frequently about Swedish saxophone improviser Mats Gustafsson and his amazing flexibility--how he can veer from bulldozer blats to pin-drop whispers in a single, supremely logical heartbeat. But only recently have I realized just how flexible he is on a larger scale--how he can adapt to just about any musical situation without surrendering an iota of personality. Gustafsson recordings have been coming nonstop lately, and they handily prove my point. Background Music (Hatology), a gorgeous trio recording made at the Northwestern University radio station with drummer Kjell Nordeson and local reedist Guillermo Gregorio, tools brilliantly with west-coast cool, using its light tone to explore delicate but decidedly abstract interaction. On Stumble (Wobbly Rail) Ken Vandermark meets Gustafsson's AALY Trio (with Nordeson and bassist Peter Janson) and joins him in scalding-hot, soulful unison freebop lines that explode in bursts of concentrated relief. Frogging (Maya), a duet with bassist Barry Guy, is knottier: Gustafsson answers Guy's punishing arco strokes and volcanic pizz-thwacks with low-end blurts and piercing screams--often accented by actual vocal interjections fired through his horn--but he also lays down long, slow ropes of sound that tie everything together. The brand-new One to (Two) (Okka Disk) features Gustafsson in a completely different duo, doling out pops, coos, cries, and snorts in a marvelously considered set of improvised miniatures with cellist and trombonist GŸnter Christmann. And on his beautiful solo outing Impropositions (Phono Suecia), he makes great use of techniques like reed popping, spilled air, and key tapping. Gustafsson will appear in an equally wide variety of settings during his weeklong visit to Chicago. On Thursday he'll perform in a trio with percussionist Michael Zerang and guitarist John Corbett and also with Battuto, his quartet with Corbett, cellist Fred Lonberg-Holm, and violinist Terri Kapsalis. Based on the latter group's forthcoming album on Random Acoustics, a thrilling ride of tangled strings and roller-coaster swoops, Gustafsson's reeds here will probably sound like anything but. Next Wednesday he'll perform solo; expect some interpretations of Steve Lacy tunes. And Friday after next, in a free concert, he'll play sax-harmonium duets with David Grubbs in a preview of their collaboration, Apertura (Blue Chopsticks). Thursday, January 21, 9:30 PM, Nervous Center, 4612 N. Lincoln; 773-728-5010. Next Wednesday, January 27, 7 PM, Empty Bottle, 1035 N. Western; 773-276-3600. Friday, January 29, 7:30 PM, Claudia Cassidy Theater, Chicago Cultural Center, 78 E. Washington; 312-744-6630.