Jump to content

Optical Sound Resync Issue with Scanned 16mm Print


Christian Flemm

Recommended Posts

Hi everyone -

In the last six months I've had two 16mm release prints from my personal collection scanned in 2K. The picture and optical sound track files were returned separately, and in both cases have proven impossible to re-sync digitally (if I sync one shot perfectly, the next shot, or the scene two minutes previous, is suddenly out of sync by roughly a half second or more). I thought it was a fluke on the part of the lab in the first case, but now that it's happened a second time, I'm really not sure what the issue could be. Any ideas?

While I cannot confirm how the optical track on the first print was digitized, due to an issue with the lab's scanner the optical track on the most recent print was recorded by hooking up a Zoom H4n audio recorder to a 16mm projector that was running the print.

Any clue as to what the problem could be? Both prints were scanned at 24fps, with both optical tracks at a sample rate of 44.1 kHz.

Best,

Christian

Link to comment
Share on other sites

The soundtrack needs to be scanned on the same machine, at the same time as the picture - OR - the device used to capture the sound needs to be exactly 24fps. A projector is not. 

It's the same as shooting film and recording double system sound: the camera and recorder both need a common, accurate, and consistent speed. This is achieved in cameras with a crystal controlled motor. In digital recorders, the clock inside the recorder ensures it's in sync.

Projectors have no such mechanism (at least none I've ever used), so it's no wonder the sound is drifting from picture. 

Edited by Perry Paolantonio
Link to comment
Share on other sites

I think the only way to do this without a rescan would be cutting up the sound into separate shots  and, matching sync by eye, shot-by-shot. It would be very laborious.

Only certain projectors were externally speed-controlled, when running separate magnetic sound in sync, but even then the requirement was that they ran frame-for-frame- the speed could still vary. +/- 0.3% is quoted for my Steenbeck. That's about 0.1fps, potentially a few seconds over your 2-minute scene.

Link to comment
Share on other sites

1 hour ago, Mark Dunn said:

I agree- if you were promised an in-sync sound transfer, you should get one.

Sounds (!) like the picture scan and sound transfer have been done separately.

They were done separately, owing to a problem with the scanner.

I've a long relationship with this lab and we are all friends. Resyncing the sound won't be as laborious as you might think.

Thanks again for all the advice!

  • Thanks 1
Link to comment
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now
×
×
  • Create New...