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Audio Drift Round Triping through Pro Tools
Hi,
I working with a group that is using the following workflow:
1) Creating Sequence at 24fps.
2) Source material is Still graphics whoch are cut together to create animatics.
3) Audio is exported as OMF for Pro tools.
4) Pro Tools edits and adjust audios and outputs New master file as AIFF of matching timebase of 24fps (AIFF)
5) That file when drifts (behind) in comparison to the original source audio when cut in as a matching track on the FCP timeline. The lag is not constant and incrases over the duration of the timeline. I have made sure that Sample Bit Depth and Sample rate matches all the way around.Any clue as to what could be causing this?
Thanks,
Alex
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5 Replies
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Hi,
It sounds like Sample Bit Depth and Sample rate doesn’t match…
But if you are sure you have it correct i can only give you a tip that i always use:
make a 2 frame “blip” in both video and audio 2 sec before AND after your movie.
make it out of colour bar or a white frame + test tone BEFORE you export to OMF.
And if you use video in Pro tools you can see if your transfer is successful.
I always keep the “blips” until I export back from Pro Tools.Don’t now if this is to any help to you but I hope you get rid of your drifting.
Andreas
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You working @ 23.976 and ProTools working @ 24.0?
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Hi…
Thanks for the feedback so far.
Every indication is that we are 24fps all the way across the board.
Updated info: This project started in FCP 5, was exported as OMF, and the resulting OMF file from Pro Tools is being brought into a FCP 6 timeline.
In fact when we bring the file back into FCP 5 system, it works fine.
The only other variable I can point to is an AJA Kona 3 in the FCP 6 system that is not present in the FCP 5 system.
However, I made project on the 6 system that ignored the Kona and the issue persisted.
Since they are primarily doing cuts only at this stage, we may be able to rescue this by taking the 6 project back to 5 via XML and importing the audio there and then bringing it forward again inot 6 once it’s all matched up.
If anyone has ANY other ideas I’m certainly open.
Thanks,
Alex
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Hi Guys…
Another source has suggested that the difference in this case may, in fact, be the Kona Card.
The Kona may be trying to do do Pull down on the audio in the timeline, playing it at 23.98 as opposed to true 24.
It was suggested to reduce the speed of tne clip in the timeline by .1% So I set it to 99.1%
Wow, very close, less than a frame latency, so it sounds out of phase with the original. IMHO if you shut off the original it might as well be lined up perfectly as far as A/V sync in concerned.
However, this still FEELS like a work around to me.
Can’t I force the Kona NOT to do this?
If not, perhaps there is a more accurate time compression we could use in the Pro Tools stage to make this dead on.
Thanks,
Alex
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Further testing indicates the following:
1) FCP 5 – No Kona Imported Audio sounds fine No delay
2) Import that PROJECT in to FCP 6 and the same audio exhibits the drift.
3) Take the same FCP 5 Project and export a new Audio File from FCP 5
4) Import the Audio Exported from FCP 5 into 6 and it works fine.So we have a SOLUTION to the problem, albeit a work around, the quality is there.
But based on everyone’s thoughts….
Do I chalk this up to a FCP 6 bug?
I did my best to take the Kona out of the loop, short of conmpletely uninstalling the drivers on the fcp6 system. Using built audio abd video monitroring all the way. Could it somehow still be a factor?They are also running QT 7.2.0 on the FCP6 station. Could this be the culprit?
Your help is greatly appreciated…
Thx..
Alex
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