Whether you want to call it godfather, granddaddy or elder statesman, Chicago's instrumental outfit Tortoise will always be listed among modern post rockers as a primary influence. Since forming in 1990, this collective has made a permanent home in the middle of left field, pulling everything from dub, jazz, electronica, classical and ambient noise into a melting pot of avant-garde grooves and indie-prog rock. Whether laying down a 20-minute epic or a piece of beautifully quick mood music, Tortoise has turned plenty of corners in its musical creativity and orchestration. Making a stop in Richmond behind its most recent record, “Beacons of Ancestorship,” Tortoise is scheduled to play at the Canal Club on Thursday, Sept. 9, at 7 p.m. $15-$18.