-
Audio sync problem
So we’re working with Final Cut Studio 6.0.2, a Canon XH-A1 and a SoundDesign (don’t remember the model number) for backup audio.
So we recorded the audio on the Sound Design at 44.1 khz, 16 bit .wav files. Later on, we realized that we should have done it in 48 khz, but we figured it wouldn’t be a problem because FCP is normally pretty good with those things.
We brought in our HDV footage from the XH-A1, the audio was 48 khz. Tried to sync up the audio from the SoundDesign in Final Cut. Sure enough, there was a noticeable drift that became more and more pronounced the further we got into the project (the whole sequence is 2h30m).
I tried to convert the Sound Design files from 44.1k to 48k in Quicktime, iTunes, Episode, ffmpeg, FCP and Compressor. None of them cause the file duration to change, none of them solve the problem, no matter what I do, and no matter what they SAY the file sample rate is, nothing changes.
If there is something simple I am missing, please let me know. An audio engineer I know suggested that I take my 44.1k files and manually record them onto a different source, like a DV tape, and then capture those into FCP at 48k, but I guess I don’t understand the theory well enough to see how this would help, since the duration should remain consistent there too. As that would be a 5 hour minimum endeavor, you can see why I’d like to avoid it. We don’t have Pro Tools at work…
Any thoughts?
-
5 Replies
-
Firstly, converting the files from 44.1 to 48 is best. Don’t let FCP run with the 44.1 files. Forget the dub to DV route. Waste of time and it won’t solve the problem.
You didn’t mention the frame rate your video is shot at but frankly that shouldn’t matter. The drift must be poor crystal sync between the devices. Does the file need to stay in sync for the whole 2hrs30mins? Crystal sync over this time duration would be extraordinary. Basically you have two unreferenced devices relying on their internal accuracy.
Best bet is to calculate the drift over time and then work out a varispeed ratio that will get the two into sync. ( you can do this with a calculator). The vari should be applied to the Sound Devices audio files and an audio tool, not FCP would be the better place to create new files with that varispeed.
-
The video is 29.97 and is three separate tapes. The sound design made five separate wav files, each 39m50s. I tried the 44.1 to 48 conversion but it didn’t seem to work and sync starts to drift five or six minutes into the first file.
I’m unclear about what you mean in the ratio. My next recourse was going to be doing a speed change in fcp on the 48k files to get them to match the camera, assuming the drift is consistent
-
Michael Gissing wrote:
“You didn’t mention the frame rate your video is shot at but frankly that shouldn’t matter.”It does matter at least the difference between NTSC or not NTSC
Michael Gissing wrote:
“Crystal sync over this time duration would be extraordinary”It isn’t. Sound Devices and other vendors do follow the specs which allow less than a second drift over 24 hours (at normal temperature)
Converting the files to 48 kHz should be done with a professional audio package which keeps the BWAV header intact.
But I don’t think it’s needed.So here the standard procedure:
Go to the Audio/Video Settings.
Select a setting which matches your video codec and frame rate.
Duplicate and and replace the “Copy” with 44100 Hz
Edit the new setting and change the Audio to 44.1 kHz.
Close.
Go to the Summary tab and do the rest of the setup
Create an Easy Setup.Delete all the audio from the project.
Save and quit Final Cut.
Open your project again and import the audio.That normally works – audio import is very sensitive. Your settings have to match exactly otherwise audio playback speed is misinterpreted.
Andreas
Spherico
https://www.spherico.com/filmtools -
Andreas, I tried it exactly as you suggested and it’s still giving me exactly the same problem…
The main issue I’m finding with these solutions is that none of them actually seem to alter the duration of the .WAV files and unless I’m missing something big, the files aren’t magically going to sync themselves without some demonstrated change in duration…
Any other thoughts other than a speed change in FCP?
-
Casi,
You may try the BWF2XML demo from my website. The demo works for 30 days and will convert 10 files at a time. So it should work for you.
What the app does is to pack the audio into a QuickTime container with a QuickTime timecode track. The timecode track does tell Final Cut how to play the audio. This works fine in any case (at least if don’t mess the settings). There are several of the Blockbusters in the US which did use this method and the software.Andreas
Spherico
https://www.spherico.com/filmtools
Reply to this Discussion! Login or Sign Up