Tonight at the Whistler the long-running but low-profile local quartet called Leaves will celebrate the release of a new self-titled album by playing a free farewell show. The band’s saxophonist, Charles Gorczynski (who also plays in the duo Colorlist with Leaves drummer Charles Rumback), is moving to Oakland, California, in July, and the band is calling it quits. (Colorlist will carry on despite Gorczynski’s relocation.) It’s a shame, because Leaves’ approach diverges in a compelling way from the style pursued by most of Chicago’s improv-oriented musicians—and they demonstrate it again on the new album, recorded in 2008 and released in an edition of 100 by cassette imprint Plus Tapes.