I am puzzled by your reference to 8" and 12" here.... AFIAK 16mm cien fil could have ewither na opticla soundtrack or a magnetic one. In the fortmer case, the ausio signal modualted a light source which produced a variable width or density track o nthe film. After processing this was read using a kamp an photocell, the signal fro mthe ltter was the original audio. Or a magnetic soundtrakc, an iron oxide 'stripe' down the film which works like a tape recorder. Super-8 8mm film could have a magnetic soundtrack (I have never heard of opticla sound on such films). I have also never heard of any soundtrack on standard 8 ('double run 8(') or single-8 film. There is aslight techncial problem in that the film moves in jerks (each frame is held i nthe projector gate for projection, then the next one is moved into possition), whereas the sound recording needs a steady motion. The solutuion is the obvious one, Adter goinging throug hte projector gate there is a loop of film, the otuput side of that lopp is then moved at cosntant speed past the audio reproduction device. The loop acts as a 'buffer' between intermittant and continuos motion. -tony