Conform 29.98 Audio to 23.98?

[joe hedge]

Being told by producers, after 6 months of editing, that the audio for their 23.98 Red shoot was externally recorded at 29.98, and that the audio post house is saying everything is out of sync. Is that possible? The editors spent 6 months editing, and now when it goes to the audio post house, everything is suddenly out of sync?

 

[Mark Allen]

I'm guessing the editors were using the audio from the camera and the audio people are now trying to conform that to audio recorded on a separate system like a nagra? Sounds like it. thing is... you should still be able to synch according to the clapboard unless I'm totally missing something.

 

[joe hedge]

Like I said, they've already spent 6 months editing - I syncced everything last summer. Nothing was out of sync. Only now are we noticing that about 2/3 of our audio was recorded at 29.98, and that audio post house says everything is out of sync. Do I need to use Cinema Tools or something to conform the 29.98 audio to 23.98?

 

[Jesse Korosi]

Recently I had a job shoot on a 7D, the audio was recorded at 29.98 externally and the video at 23.98, just like your issue.
The software I used to convert the audio before syncing was Wave Agent.

The editor was happy with the way the syncing worked after the conversion. Mind you the job has yet to Online. We noticed the sync issue right away while trying to use the unconverted 29.98 material, so that is strange that it would have seemed fine at first if your editor was actually cutting with the files you synced.

 

[Bal Deo]

Using cinema tools will change the pitch not the right tool. However soundtrack will do the trick. Use the time stretch feature.

 

[joe hedge]

Forgive my possible misconceptions here, but won't time stretch make the audio clip longer? I think all we need to do is change the time code of the clip, from 29.98fps to 23.976fps. The audio clip, recorded separately from the video, doesn't need to change in duration, we just need to use a different time code base to count the frames.

 

[Michael Romano]

Wave Agent or ProTools. The former just deals in TC (I think) and the latter will actually perform a time pull. ProTools will allow you to perform a pull on an entire project by punching in the info. If you have mixed material throughout the project its going to be harder. I normally recommend just syncing the dual system audio before even cutting if possible, you'll find it out super quick where they f*cked up on set.

Note:
ProTools LE/M-Powered won't natively have these options present! Get HD or use DVToolkit.

 

[MichaelP]

Sync drift shouldn't be an issue if both rates are truly 23.976 and 29.97. Picture can be +/- 1 frame but never drift. This is a typical matchback scenario.

Michael

 

[Brian Ferguson]

Being told by producers, after 6 months of editing, that the audio for their 23.98 Red shoot was externally recorded at 29.98, and that the audio post house is saying everything is out of sync. Is that possible? The editors spent 6 months editing, and now when it goes to the audio post house, everything is suddenly out of sync?

29.97 and 23.97 are compatible timecodes.
But you can change TC base after the fact. Here is a link to a WAV file utility that does it. You may want to practice on copies of the files instead of originals.

http://www.sounddevices.com/download/waveagent.html

5 minutes of audio is always 5 minutes long - changing the timecode does not change the length of the audio file. The timecode is just a stamp on the metadata from the first frame and the code for each frame is figured out mathematically.

Here is a link to a great sound forum of pros who discussed this at length.
http://jwsound.net/SMF/index.php?topic=5647.0

 

[Mike Paul]

It is important to determine just what they mean by "out of sync". If they manually spot a file in the edit timeline and it "drifts" out of sync noticeably after a couple of minutes, then it's really more of a sample rate issue.

23.98 and 29.97 are compatible rates, as has been stated, in that a second of audio recorded with 23.976ND timecode and a second of audio recorded with 29.97ND will match. The TC numbers will drift between the two during that second (since they are counting a different number of frames per second), but in the end, a second is a second.

Now, if the audio was mistakenly recorded with 29.97DF (Drop Frame) code, then they won't match and Wave Agent should fix that right up by changing the rate stamp in the bext header of the file.

Another possibility is that you may have shot at 23.976, but edited in a 24P (true 24 frame) session and then tried to match back the original audio. In this scenario, the visual image has been adjusted by .01%, and the audio files will have to be adjusted by the same speed to match.

Honestly, I can't think of a Post House who couldn't have figured this out in about 10 seconds