Audio Drift

[Redford Givens]

Audio Drift
by Paul Turlick (Paul) on Oct 10, 2008 at 4:01:25 pm

Hello all-

Here’s the scenario. I’m digitizing DVCPro HD footage on set with a Mac Book Pro to a 1TB GRaid. All went fine on set. (Digitizing via FW I might add from a 1400 deck). Brought the footage back to the studio and and copied to my mac Pro and some of the audio was drifting. Set the capture offset for 6 frames and that seemed to help.

Things were then transferring fine (from laptop to tower) but now at the end of the day it’s drifting again. The scary thing is, as you all know, there is no consistency. It works fine and then all of the sudden a clip will drift. Now I even saw the audio drifitng on the laptop and not on the copy.

Any thoughts?

Both machines running the the same version (6.04)

TIA-
Paul

This might help. We had a lot of sound sync problems. The out of sync condition had the sound in front of the video and then behind it in the same clip. It was impossible to re-sync the clips.

The problem was apparently caused by capturing long segments.

When we switched to doing batch captures, the sound sync problems ended.

One thing we discovered was that the sound sync problem did NOT come from the camera. When we played the bad clips in the camera there was never one iota of drift etc.

This might correspond to the “deck” you are using providing good sound on the set and then having things go bad when put into FCP.

I’m hardly an expert, but Dave LaRonde’s suggestions below worked perfectly. We’ve never had a sound problem since.

We went back and recaptured the bad segments using the batch capture method. Voila! No more sound troubles.

Recapturing is far less brain damaging than trying to reposition a sound track that varies in how far out of sync it is from minute to minute. Attempting this risks severe brain damage!

Capturing long segments also causes Time code problems, but batch capturing cures that too. (Just note where the TC break occurs and recapture a few seconds earlier or later.)

The inability to reliably capture long clips is a flaw in the FCP system and should be addressed by Apple.

Maybe this will work for you.

Re: audio sync problem with DVX100B
by Dave LaRonde on Aug 18, 2008 at 11:09:28 am

On those very rare occasions when I have to deal with 24pa, I’ll stick with the tried and true: DON’T capture entire tapes. DON’T capture groups of takes. Log individual shots only.

Yes, it takes longer, but the batch capture is a breeze, and it always comes out right.

Dave LaRonde

Thanks Dave. You are exactly right about batch capturing.

Now that we figured out how to do batch captures, the sound and TC problems have vanished.

Batch capturing saves us time because there are many bad takes that have to be removed. With an accurate video log we just capture the good stuff and it saves time.

Thanks to everyone for the suggestions. We went round the bend with sound-sync and TC breaks, but due to you folks we now know more about TC breaks and sound-sync problems than we ever wanted to learn.

Kill all robots

Redford Givens

[Kevin Monahan]

Long capture synch problems have been around since FCP 1. Always better to log and batch capture.

Kevin Monahan
http://www.fcpworld.com
Author – Motion Graphics and Effects in Final Cut Pro

[Paul Turlick]

Thanks for the insight. I am, however, batch capturing relatively small clips. Still haven’t gotten to the bottom of it……

[Ed Cilley]

My problem is slightly different, but has similar issues.

Captured BetaSP footage via AJA IO into FCP 6.0.4.

While playing back the clips, audio immediately starts to drift. Towards the end of the clip, video goes to black and audio continues. The same is true for clips 19 seconds long or 3 minutes long (the black is proportional to the length of the clip).

Here’s the weird thing. The QT clips play fine outside of FCP — they are in sync in the QT player. Inside FCP the audio drifts and is out of sync.

I have uninstalled the AJA IO software. Trashed my FCP preference using FCP Rescue 6. Restarted. Launced FCP, changed Playback Control;Frame Offset to 0. Still have same issue.

Any ideas?

Thanks,
Ed