High Quality Content by WIKIPEDIA articles! Sound follower, also referred to as Separate magnetic, SEPMAG, Magnetic Film Recorder or Mag Dubber, is a device for the recording and playback of film sound that is recorded on magnetic film. This device is locked or synchronized with the motion picture film containing the picture. Sound follower operates like a analog reel-to-reel audio tape recording, but using film not magnetic tape. The unit can be switched from manual control to sync control where it will follow the film with picture.