In free improvisation at its best, musicians engage in an alchemical conversation that predicts musical gestures as much as it reacts to them. The Austrian quartet Polwechsel–trombonist Radu Malfatti, guitarist Burkhard Stangl, cellist Michael Moser, and bassist Werner Dafeldecker–are not only masters of the sensitive give-and-take, but they apply their sublime skills in a fascinating exploration of sound. As heard on their 1995 debut, Polwechsel, they don’t merely revel in exciting and unusual textures, they obsess over them. Their music consists of tiny, highly detailed studies in which the smallest gestures and fragments take on lives of their own: Malfatti uses a flatulent column of air to initiate a rich musical dialogue; Stangl’s percussive guitar thwacks are followed by like-minded abstractions from the rest of the group. They rarely produce sounds you’d expect from their instruments, and the dynamic use of silence heightens the intensity of the most fragile sounds. Listening to Polwechsel requires full attention, but the group’s gorgeously unique approach rewards rapt ears. Polwechsel performs as part of the Empty Bottle Festival of Jazz & Improvised Music on Wednesday, 9 PM, Empty Bottle, 1035 N. Western; 773-276-3600. Malfatti and Dafeldecker will perform with local improvisers Gene Coleman, Jim O’Rourke, Kevin Drumm, and Michael Cameron on Friday, 8 PM, RX Gallery, 1464 N. Milwaukee; 773-227-2215. Saturday they’ll play as a duo, 8 PM, Renaissance Society, Cobb Hall, University of Chicago, 5811 S. Ellis; 773-702-8670. PETER MARGASAK

Art accompanying story in printed newspaper (not available in this archive): Photo of Polwechsel by Jerzy Palacz.