Reading Dolby Digital AC3 from an entirely digital film scan

[David Ferguson]

The thing is, the output from the CAT699-702 is an analog video signal, not a digital signal. If you want to feed this back to a DA20, then you need to replicate this analog signal from the already scanned and digitized data, which is a bit of a detour, actually, a rather hefty one. Creating an analog signal that passes muster for the DA20 input circuitry will probably require quite some reverse engineering too.

it certainly is a detour and would require reverse engineering the video format, but it may actually be the easiest way of achieving the goal of “read a scanned SRD track”. My goal when I started this was “understand how it all works”, but if you’re just trying to read it, having a device that generates analogue video is probably not too hard. Analogue video is very well understood and not hard to generate - I’ve used microcontrollers to generate composite video and CRT tube patterns before… it probably wouldn’t be a massive project to work out what the SRD video format is. However I know that the CCD in the SRD readers is very sensitive to being unplugged/plugged so I wonder if hooking up a scope to it would cause any issues… but I assume not, since that’s exactly what you’re doing when you align it.

I’d also rather want to go the route of decoding the digital data stream. I think David's idea may be worth a shot. I'll try to contact some people who I know at certain archives, maybe a group effort, asking Dolby to release this codec for archival purposes, may trigger something...

If you have contacts that are interested in this, that would be curious to see if Dolbys position may change. I have a couple of contacts on the Dolby side of that helps - let me know how this goes. And if you’re able to share any images from the scan that would be great - even if it’s cropped to just be the SRD blocks and sprocket holes!

Would a Dolby Digital simulator - those boxes to test the input of a sound processor - be of any help maybe? Whatever it's generating, it happens digitally inside.

I don’t think it would especially help - it’s easy enough to run film through a reader and hook up a scope to see the video signal. However if anyone has one they want to sell, I’d be interested in adding it to my collection of oddities!