DV and DAT Audio Sync

rtbond wrote on 8/2/2009, 5:33 PM

I have a DAT audio recording of a concert (from 1997), as well as a two camera video shoot (DV format). The DAT audio was ripped to a WAV file by a friend.

I am trying to use the DAT audio to replace the camera recorded audio, although I can't keep the audio from the DAT recording in sync with the video.

Within the duration of a 5 minute song the DAT audio noticeably leads the video.

Any idea what is causing this behavior and what options I have to try to correct it?

Comments

Steven Myers wrote on 8/2/2009, 5:49 PM

You don't say how much difference there is in time between the DAT and the DV audio. If it isn't too extreme, you might be able to do this without noticeable artifacts. You also don't say what kind of concert it was (if it's death metal, you're in luck!)
Put them both on the timeline and stretch the DAT audio to match the other. The waveforms won't be identical, but they should be similar enough to give you some visual indication of how close you are to the right amount. Listen and adjust.

farss wrote on 8/2/2009, 5:56 PM

A not uncommon problem as the clocks in the cameras and the DAT will not be running at exactly the same frequency unless they're genlocked.
To fix this sync the start by slipping the audio track. Then sync the end by using Ctl + drag to change the length of the audio track. How easily you'll accomplish this depends on the availability of visual or audio cues to provide sync points.

It can get more complicated if the clocks were drifting. They should be close enough over one number. What I sometimes have to do is to resync each or several numbers. It's unlikely you'll need to do this, modern kit is pretty good if left to warm up before the show.

Bob.

musicvid10 wrote on 8/2/2009, 9:27 PM

Stretching or shrinking the audio may be OK for noncritical work, but doing so introduces artifacts, mainly quantization noise, that may be objectionable for music tracks.

Also, on a long program, syncing to a point near the beginning and end by that method may not be enough, as the audio tends to drift ahead and behind within the constraints.

My preferred method is to split the audio approximately every ten minutes, being careful not to cut where the gap will be noticed, then line up the approximate center of each clip with the camera audio waveforms. If done carefully, the microgaps will not be noticed, or can be filled with adjacent material in Sound Forge.

rtbond wrote on 8/3/2009, 5:02 AM

Thanks for the explanations and techniques for adjusting sync.

I'll probably split the audio at every song and make the appropriate ctrl-drag adjustments to the DAT track to keep in sync with the video.

--Rob

PeterWright wrote on 8/3/2009, 5:44 AM

Yes, Vegas does this incredibly well and easily ...

- do any other NLEs do this anything like Vegas?

farss wrote on 8/3/2009, 6:46 AM

"do any other NLEs do this anything like Vegas"

I can't say for certain but probably not. Then again others do a heck of a lot more to support audio for film and video. If the OP's DAT tape was from a pro DAT recorder that also recorded timecode he'd be out of luck making any use of that in Vegas. With another NLE he would have avoided the need to sync.

BTW, there's a very neato plugin for FCP that does auto sync for multicam. I've only seen the demo but man that's impressive stuff. Just throw X camera files and a wild audio track onto the T/L and let it do its stuff and it gets everything lined up using vision and audio analysis.

Bob.