Audio shifting out of sync in FCP 7

hello LACPUG!

I'm an assistant editor at Best Boy Entertainment in Canada. We've noticed a problem with syncing audio in FCP 7 that we haven't really seen or heard of anywhere else. It's footage shot on a Canon 5D MK2, transcoded to ProRes 422, and then synced with audio using the slate clap and in/out points. Here's the problem: the recorded audio seems to shift ahead of the camera's audio, by a different amount each time. It appeared fine and in-sync at first, but when the project was copied to and opened on another machine, it all went out of sync. Literally the only difference in the projects is a few bins were changed to different labels. We think that it may be taking the in points from where the original recorded audio starts, not the ones we've created in the project, and syncing it with that, thus shifting it ahead by the differences in points. Again we're not entirely sure what's causing this, so any feedback or suggestions is greatly appreciated!

Cheers,

Christian Davis
Assistant Editor
Best Boy Entertainment

Are you using a USB drive? USB can't be used for editing and may result in playback stutters that cause sync drifts.

Possibility #2: Did you use an MP3 recorder for the audio? If you tried to use MP3 directly in the sync timeline, it could also result in the problem you're seeing.

Possibility #3: Did you use the H.264 clips from the Canon 5DmkII directly in your FCP timeline? That is a big no-no.

The problem you're describing sounds like timecode issues, which can happen with any format that wasn't designed for editing (H.264 video, MP3 audio).

I use Canon DSLR footage by transcoding to ProRes 422 or ProRes 422 HQ first. I've synced it up with a variety of WAVs, AIFFs and MP3-sourced files from various audio recorders, always converting to 48kHz WAVs or AIFFs first if they aren't already. Never had a problem.


www.derekmok.com

There's also a fun little issue that can crop up w.r.t how FCP interprets frame rate on audio clips.

Open up one of the problematic audio clips and see what frame rate FCP thinks it is. If it doesn't match your footage, that could be the problem.

FCP will assume the audio frame rate of clips without TC or a source is whatever the current sequence setting is.

It's the fact that you've moved from system to system that reminded me of having this problem once.

Can't say it makes sense.

I remember that the only way to fix the audio rate in place was to add a source to the files.

ak
Sleeplings, AWAKE!

hey,

no, not using USB, should've been clearer on that. We have a server where all of our media and projects live, usually work off of our desktops and then save copies to the server. The audio was recorded with a boom mic into a mixer, as 48 kHz. WAV's. We set up our projects so that only Pro Res files make it in, no importing of H.264 whatsoever. Our Easy Set Up is customized so every sequence created is Apple Pro Res 422 1920x1080 23.98 fps.

It's not what you recorded them at that might be the problem. It's what FCP thinks they are that causes problems.

Audio recorded on H4Ns, 744Ts or any other recorder isn't broken up into "frames" in the recorder. There may be metadata that indicates what frame rate it was tagged at but the job of dividing audio up into frames happens when you import it into FCP or any other editing system. Up to then it's just a continuous stream of samples.

Just check the audio files in FCP and see what frame rate and sample rate FCP thinks they are. If you can do that and eliminate that as the issue, do it and move on to other possible roots of your problem.

ak
Sleeplings, AWAKE!

> It's not what you recorded them at that might be the problem. It's what FCP thinks they are that causes problems.

Yes, I've seen that as well. FCP can be a bit inconsistent in how it deals with material that doesn't have an actual frame rate. It may have "assigned" an incorrect one. Flat graphics files (eg. Photoshop and TIFF files) that have no time element, for example, can be affected by what the Capture Settings were set at at the time of import, so it's worth checking.

> We have a server where all of our media and projects live, usually work off of our desktops

"Desktop" means you're using the internal system drive, which is not a good practice. Sure your system drive isn't filling up past 90 per cent? Even if not, I would usually use at least a RAID 0 for ProRes at 1920x1080.


www.derekmok.com

I have seen this a lot, and am thankful for the mentioning of what to look for. One of the solutions I have found (Someone told me) with this is to handle the audio and picture to the same length before/when you sync them. So they don't have those groovy red offset lines.

And that has resolved the problem in the past.

Sync drifts usually happen due to the 0.01% slowdown in NTSC land. Don't ask me why FCP thinks 25 fps audio needs to be slowed down by 0.01% to keep sync with NTSC, because they obviously don't need to be. The only cases I can think of where a slow down (or over sampling of audio is required), is if you are shooting 24fps film or 25fps for 23.976fps output, and if you are going to be editing at 23.976 fps.

>FCP will assume the audio frame rate of clips without TC or a source is
>whatever the current sequence setting is.

Nope. FCP will assume the frame rate based on what is set in Easy Setup on importing of the audio file, if the audio file does not already have a time code flag. If the audio file was interpreted as 25fps or has timecode already set at 25 fps, you will see a dark green render line at the top of the audio clip in the timeline. I'm not sure if that affects 29.97 fps files when imported into a 23.976 fps timeline. Anyway, when you see that, stop, delete the files from your FCP project, and re-import them, or else FCP will slow down or speed up the audio by 0.01% to compensate, driving everything out of sync.

If the wav files have been flagged incorrectly, you can change the framerate flag on the wav files by using this little app:

[www.sounddevices.com]



www.strypesinpost.com

> whatever the current sequence setting is.
> Nope. FCP will assume the frame rate based on what is set in Easy Setup

For graphics files, it's the Sequence Preset that determines it, not the Sequence Setting (since imports can be done with no Sequence open). I can't re-create the problem with audio files, though. I just did a little shoot last night with a Canon 60D, 23.98fps transcoded to ProRes 422 for editing, and audio from a Zoom H4 (48kHz WAVs). I had remixed the audio and saved AIFF versions at 48kHz, and both the WAVs direct from the H4 and the remixed AIFFs import with no predetermined frame rate, despite changing the Sequence Preset around. And I've been syncing these to five-minute unbroken performance takes and they're in sync from beginning to end.


www.derekmok.com

>I can't re-create the problem with audio files, though.

Do this. Create a new project. Set Easy Setup to a 25fps preset. Close FCP. Relaunch FCP. Import audio files. Import 29.97 fps video files. Drop 29.97fps video files into a 29.97 fps timeline. Drop audio into that 29.97 fps timeline. Presto! Dark green render bar. Check sync. Sync drifts.

I see that all the time here in PAL land whenever we need to do 29.97 fps jobs. I'm not sure if it's sequence preset. I'm pretty convinced there's a hidden switch in the Easy Setup that does it. But of course, I could be wrong. I just make sure I have Easy Setup set up properly before I import anything into FCP.



www.strypesinpost.com