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Drifting audio problem

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andrew bernard
Drifting audio problem
on Oct 29, 2014 at 5:06:49 pm

Hello,

I have an animation project that has been built in FCP 7. My editing time base is 24, using the 4444 codec. Audio settings are 48khz 24-bit. Our soundtrack is being created entirely in ProTools, which we have been building in there around h264 exports from FCP.

When bouncing the final audio from PT and bringing it into FCP, it starts off in sync but slowly drifts out. My PT session settings are 24 fps timecode, 24 fps feet+frames, and 48khz 24-bit for the export.

The project is about 16.5 minutes long, and by the end in FCP, our audio tail pop is beeping exactly one second too early!

I am suspecting FCP is adjusting the soundtrack unnecessarily, as I am getting the exact same one-second-too- early result when I bounce a 23.976 soundtrack from PT.

Please let me know if you have any ideas, and if I can provide further info.


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andrew bernard
Re: Drifting audio problem
on Oct 29, 2014 at 6:32:48 pm

Upon further investigation, FCP seems to be playing back all my audio imports too fast. From head pop to tail pop, my soundtrack AIFF file measures 16:28. But when imported into FCP, the file length is suddenly 16:27.

Even with other similar-length audio that FCP itself has exported, when imported back into FCP, it is now 1 second shorter.

Why is FCP doing this?


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Mark Suszko
Re: Drifting audio problem
on Oct 29, 2014 at 6:42:29 pm

Depending on the codecs and the preferences, FCP7 doesn't always keep the audio sample rate you really wanted.


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andrew bernard
Re: Drifting audio problem
on Oct 29, 2014 at 6:46:23 pm

Is there anything I can try?

I read that FCP may get its audio import information not from any of your sequence settings or the audio file, but from your original "Easy Setup" settings. My Easy Setup was in fact set at the wrong frame rate at first. But I have since changed it to NTSC 24 fps, and the audio is still importing 1 second too fast...


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Michael Gissing
Re: Drifting audio problem
on Oct 29, 2014 at 8:57:52 pm

The wrong Easy Setup is nearly always the cause of sync drift like you have.

Now that you have changed the setting to match frame rate you will need to reimport the mix file with a different name. FCP helpfully remembers the file name and keeps reapplying a frame rate (incorrectly). So change the name on another computer and then reimport the new file and it should sync.

This feature in FCP has caused more grief than any potential help it has been.


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andrew bernard
Re: Drifting audio problem
on Oct 29, 2014 at 9:09:40 pm

Hi Michael,

I'd read your posts about this issue elsewhere and have been trying to fix it this exact way :)

Unfortunately, changing the Easy Setup to NTSC 24 + deleting and renaming the audio files has not done the trick yet. The mixes are still importing to FCP at the incorrect duration (playing back too fast and ending 1 second too early). I have been deleting and renaming the mixes on a separate external drive, which is plugged into the same computer. Is that perhaps not thorough enough?

I've just tried exporting new mixes from ProTools, pulled down to 47952 to accomodate for FCP's speed up. And bizarrely, FCP is still insisting on playing them back at the wrong speed, exactly like the 48000 files.


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Michael Gissing
Re: Drifting audio problem
on Oct 30, 2014 at 1:05:57 am

The other fix trick is to use Wave Agent which is a free utility from Sound Devices to change the file metadata. It is a bit like Cinema Tools in that you can change data like frame rate or sample rate within the file.

It might be that you need to tell the 47952 to flag as 48khz so it doesn't speed up and also to check that the frame rates do match. If they do then it might be that the ProTools project was not true 24 but perhaps 23.976.

Either way you should be able to fix it by changing the file metatdata.


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Michael Gissing
Re: Drifting audio problem
on Oct 30, 2014 at 1:07:59 am

There is a final hack fix and that is to change the speed of the audio by .1% to counter the drift. If you try that first it will also indicate if it is a 23.976 to 24 issue.

Whilst that will sort the issue in FCP it may not help if you make a DVD using the separate audio.


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Michael Gissing
Re: Drifting audio problem
on Oct 30, 2014 at 1:10:33 am

And finally renaming must be done on a different computer otherwise the system knows!


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andrew bernard
Re: Drifting audio problem
on Oct 30, 2014 at 5:25:22 am

Well, I don't know if the Easy Setup is still the primary suspect in this case. Since changing that to 24, brand new exports with new names from ProTools are all still playing back at the wrong speed when I bring them in to FCP.

I did the 99.9% slowdown trick in FCP and that makes the project sync perfectly from head pop to tail pop. It does seem like a bit of a hacky way to make the soundtrack sync though, and I'm not sure if it is an ideal long-term solution. Would moving forward with it like this create any compromise in sound quality?

I will meanwhile look into Waveagent, thanks... how strange that FCP has such difficulty with pure 24 fps projects.


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Michael Gissing
Re: Drifting audio problem
on Oct 30, 2014 at 5:30:08 am

No problems with sound as you are just forcing FCP to play the file at the correct speed so it should sound identical. Thankfully FCP doesn't try to change pitch. .1% is negligible pitch anyway.

The issue potentially is with any release that requires you go back to the original mix file like making a DCP or DVD/ bluray. If not then the hack is fine as the output master file at the end has the correct audio baked into the quicktime file.


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andrew bernard
Re: Drifting audio problem
on Oct 30, 2014 at 5:47:57 am

Thanks again for your help!


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andrew bernard
Re: Drifting audio problem
on Oct 30, 2014 at 5:35:39 am

Gotcha.... we will be making a DCP, but for that I will be bringing the original PT session to a 5.1 mix stage, so FCP should no longer be a factor (and the professionals there would be able to tame any weird sync problem better than me anyway!) I mainly need the mix to behave properly here in FCP for exporting stereo Quicktimes.


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David Roth Weiss
Re: Drifting audio problem
on Nov 6, 2014 at 8:25:50 pm

Once you change the settings in Easy Setup you must open a new timeline - the old timeline will always carry the old Easy Setup settings.

And, I've forgotten if there's an Easy Setup at 23.98 or 23.976 - shouldn't your video frame rate be at set at one of those and not 24fps?

David Roth Weiss
Director/Editor/Colorist
David Weiss Productions


David is a Creative COW contributing editor and a forum host of the Apple Final Cut Pro forum.


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andrew bernard
Re: Drifting audio problem
on Nov 6, 2014 at 11:27:45 pm

hi david,

ah! i did not know that about having to open a new timeline! so i would have needed to create a new sequence and import everything in from the existing one?

24 fps is our timebase because it is a purely 24 fps digital animation project with no telecine involved.


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David Roth Weiss
Re: Drifting audio problem
on Nov 7, 2014 at 4:58:17 pm

[andrew bernard] "ah! i did not know that about having to open a new timeline! so i would have needed to create a new sequence and import everything in from the existing one?"

Just remember, Easy Setups control ALL new timelines in FCP 7, while Sequence Settings do the very same thing, but only control the current sequence and and copies made from that sequence. In addition, once a sequence is open and contains footage, some of the important parameters, such as frame rate, can't be changed in Sequence Settings - the ONLY way to change them is to change Easy Setup and open a new sequence, or open a new sequence and change the parameters before adding any clips.

These are BIG things to know in FCP, because as you've already discovered, if you don't remember them you'll be scurrying around in many wrong directions finding solutions to problems that don't exist. And, these are so fundamental to FCP operation that most here on the Cow sometimes forget to mention them.

David Roth Weiss
Director/Editor/Colorist
David Weiss Productions


David is a Creative COW contributing editor and a forum host of the Apple Final Cut Pro forum.


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Jim Press
Re: Drifting audio problem
on Dec 19, 2015 at 1:39:15 am

YES!! This solution just saved me from insanity. We upgraded our editing systems a few months ago and switched from FCP7 to Adobe Premiere Pro, and in the move hadn't gone back in to FCP and changed the default Easy Setup from NTSC to PAL (we are in Australia), so when I had to do some work on an old project, all the polished audio files had drifted from the raw audio linked to the video. Changing the Easy Setup to PAL and restarting as described above solved it. Thanks guys!

MacPro 2009 6core 3.33GHz 16GB 10.6.8.Ffibre channel XSAN. Red Rocket.


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