Audio Sync Problem

ScottJames wrote on 10/10/2006, 7:24 PM
I'm shooting videos of in-studio artist performances at our radio station, using a Sony DSC-W7 camera, which produces decent MPG video -- certainly good enough for display on our website. However, the camera only records mono audio, so we're also recording the audio in stereo on a PC and saving it in uncompressed WAV format.

I load the video and its associated mono audio track into Vegas 6.0d, and then bring the stereo audio in on another track and line them up. After that's done, the mono track is nuked before the final render.

The problem is that although everything is perfectly in sync at the beginning of the session, by the time I get to the end -- 5 minutes on average -- it's way off ; the stereo track is lagging behind the video (and the mono camera audio track) by a very noticeable amount.

The camera records audio at 32kHz, and that can't be changed. We're recording the stereo WAV at 44.1, and I thought this might have something to do with it. However, I just did a test, recording the WAV at 32K, and I got the same result.

I also got the idea that it might have something to do with the fact that the stereo WAV is being recorded on one PC and then the session is being assembled on another (my notebook). However, for the 32K test, I recorded the stereo WAV on the notebook as well.

Since the camera generates MPG, I assume it's doing on-the-fly audio compression; the PC handling the stereo WAV is not. Could this be where the trouble lies?

Thanks in advance for any help.

Comments

farss wrote on 10/11/2006, 6:35 AM
Technically the sample rate shouldn't matter.
However experience seems to be that if clocks are going to be inaccurate it's most likely to occur when they're at different rates.

Given how your constrained I don't think you have much choice but to resync it by hand in Vegas.

Bob.
newhope wrote on 10/11/2006, 8:00 PM
I agree with Bob it's likely to be drifting clocks and with the gear you are using there isn't any way of curing that during recording.
Having said that Vegas is surprisingly good at duration change without pitch change by using the 'Control Drag' function on the audio. It's a case of 'suck it and see but I've had some fairly good results with similar problems.
Even on "professional" gear you occasionally get this type of problem. I had to resync the whole of Pirates of Pennzance when the three DA-88s it was recorded on didn't hold lock to the incoming video black feed off the OB Van. All this on an Audiofile back in the mid 90's.... oh if I'd only had Vegas to do it on then.....

Regard
Stephen Hope
New Hope Media