A/V out of sync

[Kevin Randolph]

I recently shot an event that lasted over an hour straight - hit record and pan with the subject, no big deal. I'm using an XL2 that I bought about a year ago. I transfered the tape to my Mac and now I'm cutting back an forth between the wide shot and the CU and tweaking the audio. About 45 minutes into the tape the audio and video are now out of sync. FCE thinks that they are in sync, and I used the same XL2 to transfer the video to the computer that shot the video. Any thoughts as to why this would happen? Or what I could do to keep it from happening in the future?

Any help would be great.

Now that I think about it, on my last project I had a slight audio drift problem, too. But I thought it was my editing because the cuts were much quicker and there was no continuos shot for reference. So I'm guessing that the issue is in the camera.

There were different audio setups for each shoot. On shoot #1 it was just the XL2 and an AT897 hooked up to the XLR channel 1 doubled to both channels in camera. On shoot #2 it was the XL2 and the same AT 897 hooked into XLR channel 1 and a Sure wireless hooked into XLR channel 2.

Just in case you're wondering, the wireless lav and the AT897 stayed in sync with each other, but fell out of sync suddenly with the video at the same time.

Thoughts?

Thanks,
Kevin

[Jonathan Jones]

Is there any possibility that you dropped frames at various points during the capture that would present a cumulative effect in time lag from the audio after a while?

That would be my guess as it happened to me a few years ago. I was doing a multi-cam project on with 6 cams captured through FCP...no problems. I also used a file from a capture that was done in iMovie and dragged it into FCP. I synced it up, but after a while, it kept losing sync.

There was very little action going on in the track, and it took me quite a while to figure out it was dropped frames, and even longer to find out where they were dropped because there was virtually no change in the image throughout. iMovie doesn't have a dropped frame detector, so I had to decide to either creep through the whole track frame by frame to find the dropped ones and cut & move the track accordingly, or get the source tape and re-capture directly into FCP. I chose the latter.

Maybe something like that has happened to you but it may take a while to scrub through the track to see if there are any intermittent frame jumps tht might indicate a dropped frame.

Hope this helps.
-Jon

[Kevin Randolph]

I forgot to mention that the editing program I'm using is Final Cut Express 2.0.3. It does have a dropped frame indicator when you do the capture. It did go off on one of the tapes of the event, but not any of the ones that I'm working with now (I'll be cleaning that mess up later today). I have been watching fairly close as I go through to track - watching specifically for sync issues as I adjust the audio levels. I haven't seen anything yet, but maybe I'm missing it.

I was just wondering if anybody else has had a similar issue with audio drift and the XL2, if the problem was avoidable, and what I did wrong.

Thanks for the advice Jonathan. I may have to go with your suggestion about doing a re-capture, but I just hate to at this point. Hopefully I won't get to the point where that's the more time effective option, but who knows.

Thanks,
Kevin

P.S. - Love your quote...

[Jonathan Jones]

Did you shoot with audio settings in standard 2 channel 16 bit/48Khz, or did you set it to 4 ch 12 bit/32 Khz?.

I have done some shooting in the 12 bit/32 Khz setting, which can result in drift depending upon how you work with it in post or how your NLE handles it, but I"ve always converted it up in post with FCE and have never had a problem with it staying locked.

If you did shoot in 16 bit/48 Khz, then just disregard this post, but if not, that may be the source of the problem and may require you to convert the audio up 16 bit/48 Khz. (Not to make it a better sounding file, but rather to help it lock to the video better.

-Jon

[Cole McDonald]

I've seen this as well in FCP if the audio settings of the footage don't match the settings of the timeline.

[Kevin Randolph]

Everything was/is set to two channels at 16 bit/48Khz. That's the only way I shoot/edit right now (no MA-300 or mixer to make things complicated). That's why this was so weird.

My timeline/sequence settings are "DV NTSC 48Khz"

Other thought?

Thanks again Jonathan and Cole

Kevin

[Cole McDonald]

um...use compressor to convert the footage to full quality quicktime (lotsa HD space) or some other format that is listed under the sequence presets to see if compressor can slap it back into submission. Other than that, I'm at a loss.

[Kevin Randolph]

Thanks for the help everyone. I was able to work through it. Turned out to be a +4 video shift that was gradual over the hour tape. Just a little time consuming to fix...

Thanks again,
Kevin

[Ian Scanlan]

Hi Kevin....glad you sorted the problem out. May I ask what you mean by a +4 video shift? The reason I am asking is that recently I experienced an audio/video sync problem. I filmed an interview taking place at a radio station with 2 canon XL2's. The radio station also gave me a copy of the audio on cd a day later. I am using Adobe PPro CS3. I found that when I synced up the XL2 wavefiles together - no problem. However, when I tried to sync up the audio from the cd to my XL2 wavefiles, there was a noticeable drift. The solution I had to do (from a PPro forum) was to increase the speed of the cd audio. That seemed to do the trick. Anyone else had this problem when matching up audio from an external device?

[Kevin Randolph]

Ian, I didn't have to speed up the audio to make it work. What I had to do was to go through the entire presentation (about an hour long) and watch for individual frame shifts. The total adjustment was that over the course of an hour I had to shift the video track ahead four frames after un-syncing it from the audio. I had two angles on the subject, a long shot and a close-up, so I only had to adjust the close-up. I don't think anyone can see a presenters lips moving on a wide shot from the back of a ballroom.

Best of luck, I know it was a royal pain in the hind-quarters to get mine fixed...

FWIW...
Kevin

[Greg Boston]

Gentlemen,

I believe what you are experiencing is one of the differences between mini-dv and other dv formats such as DVCAM.

mini-DV does not use 'locked audio' and it can drift over a long period of time. DVCAM uses locked audio which will stay in sync with picture.

The original Canon XL-1 was also reported to have a frequency that wasn't quite dead on 48 khz which added to the problem.

-gb-

[Ian Scanlan]

Thanks Greg for that excellent piece of info. Just to add that the problem for me was that I had trouble syncing up my XL2 audio to audio recorded from an external device. I have never had any real trouble with a/v drift with my XL2.