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Sync audio to DVCPRO HD film transfer 720p24
Workflow question: We are shooting 35mm film at 24.0 fps. We record sound to BWF files. We transfer the film to D5 and DVCPRO HD (with window burn-in) at 23.98 fps. I capture the clips and create 23.98 fps clips. How do I sync the BWF files to the captured clips so that the sound doesn’t drift? The film is being pulled down (i.e., slowed down) when transferred to HD, so doesn’t the sound also have to be pulled down in order to sync to the clips? How is this accomplished?
massachi
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9 Replies
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Your audio does, indeed, need to be pulled down to match the slower frame rate of your transfers. The transfer house can do this for you.
Many audio recorders have a setting that records at a slightly higher sample rate, (I think it’s 48,048, but don’t quote me!), and you can simply reset this sample rate in an audio editing program to slow it down.
Your sound recordist & sound designer can give you more detailed information, based on how you’re recording your sound.
Arnie
Now in post: Peristroika, a film by Slava Tsukerman
https://www.arniepix.com/blog -
Thanks, Arnie. But I’d like to be cutting with the BWF files instead of the sound on the HD tapes. That way I can make OMF’s using the original files. Is there a way to slow down the BWF files in FCP before I sync them?
massachi
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You should get all the info on the BWF files, especially their sample rate.
You also have the option of editing in a 24 fps timeline, instead of 23.976, which would speed the picture up again to match the unchanged audio.
If you need to change the BWF files sample rate stamp, here’s a Sample Rate “restamp” tool, which runs in the terminal. I haven’t used it.
https://24p.com/AvidInsider2.htm
The most important thing is to figure out how sound will finish, and work backwards. Talk to the sound editor, figure out what they want, and then work backwards to give them the right delivery.
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I just took a quick peek into the Cinema Tools manual. There’s some good information in there about synching audio shot for film at 24 fps to video transfers at 29.97 or 23.976. Take a look, in particular, at page 138, where one thing they recommend is slowing down the audio in FCP to 99.9%.
Arnie
Now in post: Peristroika, a film by Slava Tsukerman
https://www.arniepix.com/blog -
Actually… ONLY do the speed adjustment in FINAL CUT PRO – do NOT do any stamping of the sample rates tricks with audio that is to be synced in FINAL CUT PRO. I won’t get into it at this point but results are opposite in Final Cut Pro than say PROTOOLS and there is a very good reason for this – genius actually- but just do not stamp audio to different sample rates for use in FINAL CUT PRO hoping for the fix you want. USE SPEED ADJUSTMENTS – in your case 99.9% before syncing audio to picture…
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Speed changing in FCP seems messy. Doesn’t that make the sound timecode inaccurate for EDLs and OMFs? How about this:
1. record the audio at 48.048 kHz in the field.
2. use Cinema Tools to “conform” the BWF files to 48.0 kHz.
3. Then import those clips into FCP and sync in FCPIs that workflow possible? I don’t know if Cinema Tools lets you alter audio-only clips. And I don’t know what “conforming” does to the metadata of the BWF file. But, in theory, it sounds possible to me. Anyone know about doing this in real life?
massachi
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The Sound Devices 702T recorder has a neat trick for this, a 48.048kF (F for faux, or fake, or Fostex) mode, where the file is recorded at 48,048, and timecode is forced to 30ND.
However, the file is stamped as 48kHz sample rate, with a 29.97ND timecode. Thus it will be forced to a .1% pulldown and will be accurate in Final Cut Pro syncing to a film telecine with pulldown.
I haven’t checked in a while, but I thought Cinema Tools would not conform audio only quicktimes.
Also quite a while ago, I tried to sync and make merge clips with audio at 99.9% speed. The merge clips would not work when the audio had speed change. This may have been fixed in Final Cut since then, but check to make sure.
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Steven,
Thanks for this great answer. I just need to coordinate with the sound recordist to make sure his settings are correct for what we need to do in post. And it wouldn’t hurt to test it before the shoot date.
massachi
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Absolute must is to talk to your sound post people! Not all audio systems handle 23.98 .
The time stamping of bwf files assumes real time, not .01% drift. If FCP can run at true 24 then that is what I would do.
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