Sync Problem

Hello.

We shot a music video where the singers lip synced to a playback through a boom box. Now we find that we can't sync it up on the time line. We can hear plainly that camera guide track [camera mics] does not correspond to the studio track; they drift apart pretty quickly.

My question is, first: could our problem be the result of using the boom box? For example, the disk does not spin true? If so, is there a fix that is draconian?

Second, if not the boom box theory, what else should I consider?

Regards, Steve

> could our problem be the result of using the boom box?

Possibly, but it depends on what "boombox" it was. If it's a tape, for example, then it's highly unlikely it would ever have provided for a good consistent sync source. I shot a music video with only a CD player on set, and the drift was no worse than two to three frames per minute, easy enough to adjust for. I shot another music video where the singer played guitar and lip-synced to an iPod playing back a 44.1kHz MP3 file. No major sync issues either.

At this stage, you're better off just adjusting for sync than to try to find what went wrong. If you want a safer bet next time, do a test, and use a 48kHz WAV or AIFF file from a laptop or something similar.


www.derekmok.com

Thanks. It was a CD player. There's no question I'll do it different next time.

Okay, so, you don't think a tired motor spinning that disk could make much difference. I could deal with three or four frames per minute; the problem is, this thing appears to be drifting more that.

Any other thing I should be wondering about? SD on DVX100a.

It's probably not the boom box theory.

Double-check the FCP settings (project, easy setup and FCP startup - latter means what setup is used when FCP launches).
These settings will influence audio import especially with NTSC projects or PAL 50p.
I can't give a more detailed "trial and error guidance" as I don't know enough about your project and the FCP version.

Andreas

Some workflow tools for FCP [www.spherico.com]
TitleExchange -- juggle titles within FCS, FCPX and many other apps.
[www.spherico.com]

Sorry I was a bit late, we had some discussions here and I forgot to hit the "Post message"

Andreas

Some workflow tools for FCP [www.spherico.com]
TitleExchange -- juggle titles within FCS, FCPX and many other apps.
[www.spherico.com]

Very good. We'll do that next. The project's not fancy. Just SD, NTSC. Let's see what we find there.

Thanks.

The not obvious problem is that FCP since some versions ago supports multiple sample rates.
So having a 44.1 kHz in a 48 kHz project will let you run out of sync - if the clips are a bit longer, you won't notice that with short clips.
Same will even happen with 48 to 48. Video (and included audio) does have the 1.001 playback delay, while the external audio doesn't have - which means the actual sample rate of audio linked to video is 47956 Hz internally. All NLEs do it this way.
This means the audio/video from cam will need 1.001 seconds to playback on any NTSC frame rate, while the external audio plays back in real time. We PAL guys didn't had this problem until 50p came up - still don't know what's going wrong there.
You always can go the "resample way" - both real or virtual - to make the external audio match the project settings, or create a project matching your audio, import the audio into this project and then drag it into your current project. That's easier as with other NLEs.
This will work as long as you don't need to re-connect the audio. In this case the reconnect will use - depending on FCP version - either the launch settings or the project settings - and things may go out of sync.

I know, what I said seems to make things more complicated - on the first glimpse - but if you take the time to think about it and realize that sampling rate is the "frames per second" for audio which is somehow have to be matched to the "frames per second" for video things it will get clearer.
Though there is still this f****** issue which these MXF files where audio doesn't have a constant sample rate and to make it worse it's different by vendor.

Andreas

Some workflow tools for FCP [www.spherico.com]
TitleExchange -- juggle titles within FCS, FCPX and many other apps.
[www.spherico.com]

I have to think the answer to my problem lies in your explanation. That's how we're going to proceed Monday, with all you've said in mind. Many thanks for your patient response.

Steve