When Ben Johnston caused riots in Rio in 1962 with his infamous Knocking Piece for Grand Piano Interior, a rhythmic onslaught that requires the players to beat the piano with any available malletlike objects, he was probably surprised at the brouhaha. After all, Johnston was only fooling around with ratios. “Just intonation,” he observed about the ear-boggling system of tonal expansion he’d pioneered, “is a matter of reducing pitch relations to single ratios. When I did the same with rhythms, I got Knocking Piece.” This week, pianists Liam Viney and Gayle Blankenburg, clarinetist Sam Torrisi and microtonal guitar virtuoso John Schneider celebrate the composer’s 80th birthday with a program that includes his Knocking Piece; Sonata (1962) and Suite (1978) for microtonal piano; Ponder Nothing for clarinet; and The Tavern, songs written expressly for Schneider. REDCAT, 631 W. Second St., dwntwn.; Wed., May 17, 8:30 p.m.; $18-$14. (213) 237-2800, www.redcat.org.