Marty Ehrlich first encountered Julius Hemphill in the early 1970s when he was a high school student in St. Louis. Though Ehrlich performed and recorded with BAG (Black Artists’ Group), a community-based collective co-founded by Hemphill in 1968 to foster collaboration and present music, dance, theater, visual arts and creative writing, he didn’t get to know him well until the two were living in New York in the late 1970s. Ehrlich went on to collaborate with Hemphill, particularly as a member of Hemphill’s saxophone sextet, becoming musical director after the leader died in 1995. As chief researcher for Hemphill’s archive, Ehrlich has continued to unearth a trove of previously unreleased recordings, many documented on…