In the 1960s, a quartet of Chicagoans altered the way improvising jazz groups approached form, instrumentation and structure. Originally led by saxophonist Roscoe Mitchell, the band developed to become the collective Art Ensemble of Chicago. Their recording catalogue is sizeable and diverse, but Alyn Shipton picks a way through it to find the essential discs, guided by two surviving members, Mitchell and drummer Famadou Don Moye, and their original record producer Chuck Nessa. Including archive interviews with bassist Malachi Favors and trumpeter Lester Bowie.