[tig] Fw: Syncing from Audio CD

Michael Poimboeuf mkp
Tue Apr 6 19:27:25 BST 2004

Craig Leffel said:
> I have a sync question.... and we're in a bit of a hurry. We've just
> gotten some dailies from London, and the production audio - from what
> the production company says - is on audio CD. As we don't deal with sync
> audio from CD very often, I could use a suggestion or 2 as to what to
> do. We've tried a number of things, and all are slipping out of sync.
> There are hardly any claps, and manual sync is going - not so well...

What you should do depends on what the nature of the loss of sync is. I
can guess at a few reasons why audio from CD might have problems. I'll
offer a few suggestions.

1. Genlock the CD transport.

2. Transfer the audio into ProTools and genlock that for all playouts.

3. Genlock everything ;-)

4. Make sure you're not playing back a 44.1kHz source at 48kHz or vice
versa. If you are, a simple solution is to sample-rate convert using a
ProTools plugin - but before you do that make sure it's not something else
in this list that's throwing off your sync.

5. The number one issue with productions sent across the pond is the
timing difference between 25Hz frame rate for PAL and "24Hz" (24*1000/1001
= 23.976) or "30Hz" (30*1000/1001=29.97) for NTSC/ATSC based offline. Make
sure you pull-up/pull-down your rates if you're using NTSC or ATSC
offline, i.e. run the audio at 1000/1001 or 1001/1000 multiples of the
nominal rate.

6. If you can't resolve pull-up/pull-down rates another way, a big hammer,
way to deal with the problem is to use a Time Compression/Expansion
To find ProTools plugins go to:
click on "Products"
click on "Plug-In finder"
select "Effect Type" = Time Compression/Expansion
and that will give you a list.

7. Chances are the supplier has the project on disk and can send you the
audio at whatever rate you need - don't forget to ask. If the problem with
that is doing the file transfer, you can use AAF or MXF file containers
and Digidelivery to do a secure transfer over IP.

Disclaimer - I work for Digidesign, but I'm a designer - I'm not trying to
sell you anything - I'm not going to recommend vendors or OS for you to
dial in for plug-ins.

Michael Poimboeuf
Consulting Engineer, Avid/Digidesign
mkp at poimboeuf.com
mkp at digidesign.com

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