AC3 playback sync question

[Stavrosound]

Out of curiosity, has anyone run into sync issues with AC3 when authoring DVD? I notice the audio falls behind by about 1-2 frames on playback. I've checked the following:

- Stems are dead sync with each other and picture (to the sample, pops align)
- Uncompressed printmasters are dead sync to picture (played against the QT, pops align)
- Only the printmaster regions (no dead-space around it) were selected and printmastered to Dolby Digital, again, dead sync to picture
- Neyrinck SoundCode for printmaster
- the 29.97NFD picture was encoded to m2v as 1:1 regarding framecount
- Sorenson Squeeze 4.5 and Main COncept MPEG-2 encoders used, yielding same sycn results for the final DVD

Thus, everything down to the final DVD assets are 1:1 in framecount/length/sync. The LoRo embedded into the QT retains 1:1 sync

When simulating the mux in DVD Studio Pro 4, the audio was latent by about 1-2 frames; even the burned disc retained the same issue. Any idea as to why this is happening and how to remedy it? I re-printed the Dolby to have timecode (aligned to same timecode as pricture assets), but they don't seem to detect correctly (will be trying DVD Studio later today), but I have no idea if this timecode will even help or work. I can't imagine that I'd have to throw a slug onto the beginning the picture and keep trying until sync is correct, but maybe I should?

Both the 6-channel and forced LoRo maintain the same sync offset on playback; no drift, just overall offset.

I read something on here about how video TC and Audio TC are referenced different which wound account for 1 frame shifts. Maybe there's more on that which could be elaborated?

Any assistance or insight would be greatly appreciated. It's becoming very frustrating when all I want to do is ensure sync is maintained.

PS please forgive typos/grammar...been an extremely long day going on about 4 hours of sleep

[kk@jamsync.com]

Originally Posted by Stavrosound

When simulating the mux in DVD Studio Pro 4, the audio was latent by about 1-2 frames; even the burned disc retained the same issue. Any idea as to why this is happening and how to remedy it? I re-printed the Dolby to have timecode (aligned to same timecode as pricture assets), but they don't seem to detect correctly (will be trying DVD Studio later today), but I have no idea if this timecode will even help or work. I can't imagine that I'd have to throw a slug onto the beginning the picture and keep trying until sync is correct, but maybe I should?

Have you left a couple of seconds of black at the beginning of the AC3 file? Some decoders need a couple of seconds to sync.

[neilwilkes]

Originally Posted by kk@jamsync.com

Have you left a couple of seconds of black at the beginning of the AC3 file? Some decoders need a couple of seconds to sync.

That is actually recommended by Dolby Labs too.
2 seconds of Audioblack to compensate for slow decoders.
Most DVD Authors seem to completely ignore this though, sadly.

[espasonico]

Excuse my ignorance but by 2 seconds of Audioblack you mean 2 seconds of audio at - infite level ?

I´m new to post-production and english is not my language

[doug_hti]

even 15 frames should do it.

[kk@jamsync.com]

Originally Posted by espasonico

Excuse my ignorance but by 2 seconds of Audioblack you mean 2 seconds of audio at - infite level ?

I´m new to post-production and english is not my language

Yes, that's correct.