Composer, improviser, performer, teacher, trombonist, and instrumental innovator Stuart Dempster has been an indispensable presence in Seattle's avant scene since the late 1960s.

I first encountered Dempster in the late 1980s when I found him listed in the liner notes on my LP of Terry Riley's In C. Widely considered the "big bang of minimalism," In C catapulted an entire generation of composers, including Steve Reich, Philip Glass, and John Adams, away from academic serialism. Dempster not only played trombone at the 1964 premiere, but he organized and rehearsed the ensemble that recorded In C for Columbia Records in 1968.

Dempster also commissioned two landmark 20th-century works for trombone in the 1960s. The best known is Sequenza V (1966), an early installment in Luciano Berio's series of Sequenzae that codified new standards of virtuosity for solo instrumentalists. The other, Robert Erickson's General Speech (1969), parodies General Douglas MacArthur's fatuous retirement speech ("Duty. Honor. Country."), and more significantly, brilliantly transforms the trombone into a sophisticated filter for the voice, like a big brass vocoder. "Many pieces I do sound improvised," Dempster told me last week, "but in most of them, especially in General Speech, it's notated quite carefully."

Both works grace Dempster's 70th-birthday concert, along with Andrew Imbrie's "Three Sketches" for trombone and piano, Robert Suderburg's Night Set, and another Erickson piece, the bracing Ricercar à 5 for Trombones.

Alas, a single concert can't adequately convey how Dempster remains a fresh and compelling musician by continually collaborating with dancers (ROOM with Sheri Cohen), former students (the placid duo Pran with Greg Powers), and long-time compadres (Deep Listening Band with Pauline Oliveros). For Dempster's 75th, the UW should organize a festival.