The Screening Room is offering up a weeklong retrospective of music documentaries by Robert Mugge, and they’re well worth checking out. Each day’s double bill features Mugge’s latest, Hellhounds on My Trail: The Afterlife of Robert Johnson, paired with earlier works on blues, zydeco, Gil Scott-Heron, and Al Green. Mugge is part ethnographer, part fan, and although he doesn’t get into things very deeply, he showcases communities and sounds that are a complete reason for going to his movies. Hellhounds on My Trail is keyed to a weeklong tribute to Johnson that was staged in the fall of 1998 at the Rock and Roll Hall of Fame, and a fair amount of blather seeps into the proceedings. (We’re told by the keynote speaker, Peter Guralnick, for example, that Johnson’s art “defies explanation,” which doesn’t stop everybody from trying.) Fortunately, most of the movie features first-rate musicians, including Johnson’s stepson Robert Lockwood Jr. and Johnson’s contemporaries David Honeyboy Edwards and Henry Townsend, covering the great bluesman’s compositions, and their range of energy and inspiration is staggering. The movie isn’t so much about Robert Johnson as it is about what was passed along, from one hellhound to another.