modern cinema - digital sound on analogue film?

[Will__]

I answered a question in here this morning that got me thinking about another aspect of the films used in modern cinemas. Clearly, they must have digital sound tracks. Modern Dolby and THX are all digital, right? So how on earth do they supply the soundtrack? Still on the original reel with the analogue film cells? Or does it come in digital form with some form of link up? Surely it can't? Synch problems...etc...intriguing.....

[lard]

The digital sound information is still on the film reel, in a strip alongside the film cells. A pickup head reads the info and sends it to a decoder and amp to produce the Dolby/THX.

[adz83]

Modern film reels don't have a continuous sound strip. Digital sound is located between the sproket holes used to claw down the next frame. However the picture doesn't correspond to the sound imprinted next to it. This is because audio is is a continuous sound where as when watching a film you only watch one frame at a time. If the sound were to be placed next to the frame it corresponds to the audio would keep stopping and our ears would pick this up.