video sync issues

[Daniel L Miller]

alright. i have been searching all sorts of forums all day for this, im not exactly sure which forum it falls under, i know the guys are knowledgeable because ive posted here before so im humbly asking for help again. i edit wedding videos, we shoot with two cameras sometimes two xl1s sometimes xl1 and gl2 depending. when i capture the tapes and capture the entire thing in one file. the problem comes in when im actually trying to edit. i lay down the ceremony from one camera onto track one then go and lay in the ceremony from the other camera on track two and find a sync point at the begining, usually its the first word the minister says. however, as it plays, the two get out of sync with one another. i can not understand why this happens. i never get messages of dropped frames, both video playback rates say 29.97. i dont get it. ive heard talk that cannon audio is shady at times, but that in fcp there is a fix. i havent found this magical fix yet. i have fcp 5 on a dual 1.8 g5 tower.

again, if this is not the right place for this thread i apologize. i wasnt sure where to put it. any help you guys can offer would be greatly apreciated.

[Glenn Chan]

How much is the sync off?

If it's 1frame every (half) hour, it may be because the clocks in the cameras are slightly off comapred to each other.

If the sync drift is more significant, it's probably the way you captured the XL1 footage. Turn sync adjust movies on for it.

[Daniel L Miller]

its more than 1 frame per hour. is there anything i can do to fix the xl1 capture?

[Glenn Chan]

re-capture?

or you could try syncing up the footage yourself by changing the audio speed and exporting that out. it's better to re-capture in my opinion.

[Daniel L Miller]

is there some setting im missing that will lessen the likelyhood of this problem, or is it basiclaly a crap shoot every time i capture footage from an xl1?

[Glenn Chan]

Is sync adjust movies enabled?

Do you have timecode breaks?

[Daniel L Miller]

no TC breaks, where is sync adjust, i tried searching the help file and this forum and found nothing. i must be missing something.

[Douglas Spotted Eagle]

It's a clocking error. AFAIK, only the older XL1's have the issue. I don't know that there is a magic fix in FCP, never heard of one. Sony Vegas has a "stretch" algorithm that allows you do easily deal with this, but overall, your best option is to allow the audio to be synced for as long as it stays, then cut the audio, and resync it at the key points where the drift becomes obvious.
Canopus used to offer a a fix by modifying the .ini file, but even that's not really necessary anymore, but if you've got an older XL1, it could be.

[A. J. deLange]

Each of the cameras has a time base accuracy of about 10 ppm. This amounts to 1 frame per hour. It's possible for a particular camera to be off by more than 10 ppm and its possible for one camera's clock to be 10 ppm fast while another is 10 ppm slow. Such a pair would differ by 2 frames over an hour and other pairs may be off by more or less than this.

XL1s and supposedly XL2's sample at 48.008 KHz rather than 48 kHz. This was supposed to have been discovered by the FCP engineers and reported on at NAB 1998 or 99. FCP is supposed to have a fix but I can't find an on/off button for it. Conceptually it's a simple thing to take care of. Five frames of DV are supposed to have 8008 audio samples. If FCP finds more or less (the Canon rate is rumored to vary as well as be off in the average) interpolation (resampling) between tape samples can be done to get exactly 8008 audio samples per group of 5 frames on the hard disk.

I've never seen audio drift relative to the video on a single tape but I have seen it drift between cameras. Here the answer is also resampling (stretch) or resynching as has been suggested by others.

About the only things that may help are to try to keep all the cameras at the same temperature and same level of battery charge as these effect crystal oscillator rates rate but so does the age of the crystal (i.e. new XL2 and old XL1s could be off from this effect alone).

[Glenn Chan]

The "magic fix" is the sync adjust movies over ___ minutes setting.

It's in one of the preferences (A/V or general prefs) in the main menu, not in a sub-menu.
The setting is in the upper-left part of the preference menu.

It's probably in the general preferences settings window.

2- Try search the forum at lafcpug.org
Lots of mentions of "SAM", "son of SAM", and "sync adjust movie(s)".

[Daniel L Miller]

thanks man, i appreciate your help.

edit: is SAM something is only in fcp or earlier? i have 5 and id ont see it. on the lafcpug i noticed someone say something made it seem it was only in versions prior to 4 but from the wording i coudlnt tell for certain. i have fcp5.

[Glenn Chan]

It was there in FCP4.5...

[A. J. deLange]

It is there in the main user preferences page at the top of the right hand column. It is labeled "Sync audio capture to video source if present".

[Daniel L Miller]

yeah, its checked. i know i never unchecked that. ive also heard that switchig ot NTSC Firewire Basic could help as well. so ive done that and the next time i capture ill see how it goes. thanks for all your help guys.

[A. J. deLange]

Well I went back and unchecked it to see if it made any difference and it doesn't appear to. I get 8008 audio samples per 5 frames either way and they both seem to be synched to the video.