An eclectic French avant-garde ensemble that got underway in the early ’70s, Etron Fou Leloublan juxtaposes funk bass, jazz horns, prose vocals and free rhythms to create an ever-shifting hodgepodge that’s difficult to follow — given the band’s commitment to unpredictability — but worth the effort to try. Despite a clear refusal to honor traditional musical criteria, there’s little on Les Sillons de la Terre that’s too radical for unsophisticated palates; obscurity is tempered by good humor and lightness of both sound and spirit. Challenging fun.