Call it “free jazz,” “avant-garde,” or “the new thing.” Just don’t call it predictable. Founded in Chicago in 1965 and still thriving today, the Association for the Advancement of Creative Musicians (AACM) has long been an emblem of experimental, improvised jazz. As author Paul Steinbeck describes in his new book, Sound Experiments: The Music of the AACM (University of Chicago Press), this collective came together to play and promote fearlessly original, spontaneous music. “AACM members combined composition and improvisation in unprecedented ways,” Steinbeck writes, “creating modes of music-making that bridged the gap between experimental concert music and contemporary jazz.”