You don't see Brad Williams's name on the marquee very often. He's made himself so valuable an accompanist--not only to Chicago artists (Von Freeman, singers Jackie Allen and Kirsten Gustafson) but also to visiting dignitaries (such as vocalist Sheila Jordan, who sings his praises whenever she can)--that you almost forget his ability to lead a trio on his own. Almost, but not quite: even when serving as an accompanist, his fluent touch and brainstorming improvisations invariably place him in a starring role before the first set ends. The myriad sideman gigs have instilled in Williams an undeniable sense of his keyboard: having shaped his music to the demands of so many others, he deservedly revels in his own versatility. But this wide-screen approach to piano jazz constitutes only the first and easiest approach to Williams's playing, and you ignore the fine details--the interplay of light and dark, the unusual angles, the narrative contours--at your risk. Williams never fails to surprise and tickle. His debut album, The Next Sound You Hear, made a relaxed but impressive splash last spring, not least for his easy manipulation of the trio format; that he can further explore that microcosmic musical world on a regular basis means a lucky break for us as well as him. Wednesdays at 8 his trio performs at the Gold Star Sardine Bar, 680 N. Lake Shore Dr.; 664-4215. Next Friday, November 18, at 9 and Saturday, November 19, at 8 he accompanies Sheila Jordan at the Green Mill, 4802 N. Broadway; 878-5552.