Long admired for its boss tenors, Chicago has rarely boasted a bumper crop of alto saxophonists--which makes the recent emergence of Jeff Newell all the more satisfying. It's not that Newell just showed up; in fact, he's been a regular presence on the local scene throughout most of the 80s, starring in groups led by Marshall Vente and Charles Earland, just to name two. But in the last year Newell's playing has achieved a new focus, and simultaneously acquired a strength that was only hinted at before. He now brings an authority to improvisations that, while engaging, often lacked punch; as a result, his more cerebral musical conceits have an emotional immediacy that makes his explorations genuinely exciting as well as intellectually intriguing. Newell's alto and soprano work supply several highlights on Earland's upcoming album on Muse, but his music--particularly his own compositions--is best served in the more expansive context of Newell's own quartet. The sturdy and responsive rhythm section features finger-busting forays by pianist Steve Million and is anchored by bassist Cal Drake and the versatile Charlie Braugham on drums. Saturday, Bop Shop, 1807 W. Division; 235-3232.