Joan LaBarbara is surely one of the most ardent and intelligent interpreters of experimental music since the early 70s. Not only an expert purveyor of tough vocal music herself (and an astute critic), LaBarbara has also played muse to a legion of iconoclast pioneers (and is married to fellow avant-gardist Morton Subotnick). With her trademark vocal effects--throat clicks, ululations, high flutters--she's proven realizable the elaborate and precise textures of vocal pieces by the likes of Robert Ashley, Philip Glass, and John Cage, some of which were tailored to her voice. Her Ravinia debut should especially delight Cage cognoscenti: it's a retrospective of five decades of writings by the American vanguard's most original and playful experimenter. Included in this capsule tour are A Flower (1950), Nowth Upon Nacht (1980), selections from Song Books (1970), and the whimsically titled Eight Whiskus and Forever and Sunsmell. Accompanying are Leonard Stein (piano) and William Winant (percussion). Saturday, 7:30 PM, Bennett Hall, Ravinia Festival, Green Bay and Lake Cook Rds., Highland Park; 728-4642.