Drifting audio problem

[Andrew Bernard]

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?

[Mark Suszko]

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

[Andrew Bernard]

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…

[Michael Gissing]

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.

[Andrew Bernard]

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.

[Michael Gissing]

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.

[Michael Gissing]

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.

[Michael Gissing]

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

[Andrew Bernard]

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.

[Michael Gissing]

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.