Sound-on-film refers to a class of
sound film processes where the sound accompanying picture is physically recorded onto photographic film, usually, but not always, the same strip of film carrying the picture. Sound-on-film processes can either record an
analog sound track or
digital sound track, and may record the signal either
optically or
magnetically. Earlier technologies were
sound-on-disc, meaning the film's soundtrack would be on a separate
phonograph record.