Audio Synching tips for FCP?
May 20, 2011 8:01 AM   Subscribe

Why won't my separately-recorded audio and video synch up in Final Cut Pro?

Recorded a speech on two cameras, an HVX and my new Canon 60D.

We recorded the audio on a Zoom H4n external recorder. The input was an XLR-out from the soundboard that the speaker's mic was running through.

We didn't use a clapboard (mistake!) because of the somewhat impromptu nature of things, so it's hard to synch up as it is. But I have a much larger problem.

The audio recording capability on the HVX died just before shooting began. So we have no onboard sound to synch up the waveform's with the Zoom recording.

I'm trying to eyeball it and can get a phrase pretty well-synched, but the audio later on in the timeline then falls out of synch.

I can only conclude that somehow the video and the audio are moving at different 'rates' and that it will be impossible to synch them up unless I change some setting.

I have done audio synching before and never encountered that problem. Is this possible or have I lost the plot?

Any tips or advice to shed light would be greatly appreciated.
posted by meadowlark lime to Media & Arts (6 answers total)
The internal clocks in consumer / pro-sumer electronics tend to be less than stellar, so you'll end up with things drifting between your devices over longer takes.

What you'll probably have to do in this case is break the audio up into several chucks before the drift gets noticeable and realign the audio. Re-align things before you're anywhere near a frame out of sync. Bad sync is really really obvious.

In the future, if you have to start shooting before you can get a clap in, you can always slate at the end of a take, but that still isn't going to help with the drift between the clocks in the various devices you're using. The only real solution there is better gear.
posted by jjb at 8:22 AM on May 20, 2011

I've seen Plural Eyes talked about on HDSLR blogs as a good tool for fixing sync issues. I've not tried it though.

I'm a student so this may seem like a noob question but are you transcoding your footage? I have a 60d too and I always trancode the footage to Apple Pro Res 422 before I bring it in to FCP. I use mpeg streamclip. Not sure if that has an effect on sync issues. Just throwing it out there.
posted by dorkydancer at 8:40 AM on May 20, 2011

The way I've fixed this in the past (using Sony Vegas) is to make a copy of the wave file on another line, find two obvious sync points in the new wave file, one earlier, one later and mark their corresponding spots on the video file.

Cut the new wave at the two sync points you found and then stretch that shorter cut file to fill the gap between the marks you flagged on the video file.

Now check the properties of the new wave file for it's playback rate which will have changed from 1 or 100% to another value when you stretched it.

Make a note of that new playback rate and apply it to your original untouched wave file and, alakazam, everything should be easy to line up as your wave file is now playing back at the same rate as your video file.
posted by merocet at 9:14 AM on May 20, 2011

I asked a similar question a few months ago, and got some very helpful answers.
posted by monospace at 10:26 AM on May 20, 2011

What is the frame rate of the sequence you are editing in? (Cmd+0)

Then check the frame rate of the HVX and Canon clips. (Cmd+9)

If all three aren't identical, that could be your problem.
posted by mr frosted at 11:40 AM on May 20, 2011

Look at your audio sample rates. If the timeline is 48k and the second audio is 44k (for example) your audio synch will drift. PluralEyes is excellent but I don't think it will help your drift problem. Make sure that all your elements are matching in frame rate and sample rate.

Hope that helps.
posted by jeffhanley at 10:18 PM on May 22, 2011

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