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Video is 23.98 fps on Red and Audio was recorded at 24 fps 48K

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Rachel Pearl
Video is 23.98 fps on Red and Audio was recorded at 24 fps 48K
on Apr 10, 2018 at 2:30:10 am

HI,

I've been trying to find an answer to this question in the Archives but none of the answers quite address this problem.

The video on this project was recorded on the RED at 23.98 with no camera sound. The audio was recorded at 24 fps 48 hz.

What do I have to do with the audio to let it sync up to picture in Avid without drifting? Is there a way to do a 0.1% pull down on the Audio in Avid?

If this has been answered, please point me in the right direction.

thanks!
Rachel


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Bouke Vahl
Re: Video is 23.98 fps on Red and Audio was recorded at 24 fps 48K
on Apr 10, 2018 at 7:58:32 am

Are you saying that the sound is drifting as 'getting out of sync' on long takes, or that the syncing itself gets worse during the later hours? (The latter is to be expected, the first would be a serious problem of not having genlock and really bad equipment, or someone is working @24 fps on 23.976 material, thus speeding it up.)
For correcting the timestamp, WaveAgent can do the trick. (Although you need to do it by hand for each clip)
Set the fps to 23.976, UNcheck 'keep existing timecode'.

But, sometimes Avid will ask you how to interpret the timestamp. If that happens, it's very easy, just select the right one and you're golden.

Bouke
http://www.videotoolshed.com


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Job ter Burg
Re: Video is 23.98 fps on Red and Audio was recorded at 24 fps 48K
on Apr 12, 2018 at 11:48:10 am

You just post in a 23.976p project. Sound does not have a framerate, its speed is determined by its Sample Rate. As long as the camera was running 23.976fps on set, and sound was running 48000Hz, just bring both into a 23.976p project.

Since there is no such thing as 23.976fps timecode, all timecodes (on the cam and the sound recorder) would usually have been TC24.


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Bouke Vahl
Re: Video is 23.98 fps on Red and Audio was recorded at 24 fps 48K
on Apr 12, 2018 at 12:48:34 pm

Eeh Job,
Not quite. there is a 0.1% difference in calculating BWF SAM to 23.976 or 24.
Now, there is also a flag in BWF files (that can be on or off) that forces Avid to interpret speed at a given framerate.
And my (highly educated) guess is that is exactly where things go wrong.

Bouke
http://www.videotoolshed.com


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Job ter Burg
Re: Video is 23.98 fps on Red and Audio was recorded at 24 fps 48K
on Apr 17, 2018 at 6:12:54 pm

Hi Bouke,
If the cam was running at 23.976 and the sound as running at 48K, picture and sound should sync up in a 23.976 project. Timcode counts, but does not change speed.
When recording at 23.976, to the best of my knowldge, regular TC24 is commonly used. I don’t think there is an actual 24DF timcode type. Not saying it cannot be calculated or created.


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Bouke Vahl
Re: Video is 23.98 fps on Red and Audio was recorded at 24 fps 48K
on Apr 18, 2018 at 5:56:42 am

Hi Job,

[Job ter Burg] "If the cam was running at 23.976 and the sound as running at 48K, picture and sound should sync up in a 23.976 project. Timcode counts, but does not change speed."

It should always sync, no matter the cam framerate and sound sample rate.
BUT, to calculate the TC from the BWF timestamp, it IS important to know the speed.
23.976 is a non-drop format, (Or, regular TC24 as you call it) where 01:00:00:00 is NOT a wall clock hour, but 0.1% less (Thus 3.6 seconds)
A BWF recorder does nothing different in recording the files at any speed. Only thing that changes is a tiny bit of metadata in the file (Bext entry SPEED=XXX.XXX that has not to be used).
But, of course the LTC in/output does change with the setup, and that is crucial to match the cam.
Again, nothing else is different. (Ok, in the old days you could fool Avid by setting the sample rate wrong to speed up/down for a video shoot intended for film or vice versa, but that workflow went the way of the Dodo. You might have done such a thing 15 years ago.)

But still it's unclear if the OP has problems with the start sync, or problems with drifting sound. If the latter, there are numerous things that could cause the problems.

And you know this, as on import of a BWF file you'll be asked what speed to interpret it, and you see the TC numbers change every now and then. (Not on 24 / 25 / 30 / DF, if the start is at a round second, but otherwise it does.)

Now, (at least on my system), things are different with AMA Link. Then the project speed is always used.

Bouke
http://www.videotoolshed.com


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Job ter Burg
Re: Video is 23.98 fps on Red and Audio was recorded at 24 fps 48K
on Apr 18, 2018 at 10:49:56 am

[quote]It should always sync, no matter the cam framerate and sound sample rate.[/quote] Not necessarily. There are workflows where people shoot at 24 but post in 23.976, by having the cam run 24.000 and recording sound at 48048Hz, then slowing both down to 23.976 and 48000.
Also, one needs to be absolutely sure the speed the camera was running when selecting a project type. That’s way more important than the TC rate. And my point is: the TC rate does not necessarily tell you what the framerate on set was.
Anyway. I don’t think we’re in disagreement.


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Bouke Vahl
Re: Video is 23.98 fps on Red and Audio was recorded at 24 fps 48K
on Apr 18, 2018 at 12:00:15 pm

[Job ter Burg] "and recording sound at 48048Hz"

No, huge thinking mistake. The audio is in fact recorded as 48000Hz, but flagged as if it was recorded at 48048.
Same as shooting 50 fps and put it frame by frame on a 25 timeline, you get slomo.
Hence it's very easy to 'undo' the slomo. (It's just some 12 bytes in the Wave header.)
(This is what I wrote you might have done 15 years ago...)

[Job ter Burg] "And my point is: the TC rate does not necessarily tell you what the framerate on set"

Yes and no. If you see the framecounter go from 23 to 00, of course it can be 23.976 as well as 24, so this is relative meaningles.
But normally the metadata inside the clip will tell you shooting rate, and that most of the times corresponds with TC rate. (High fps excluded, that varies per manufacturer.)
And yes, of course setting up the project to the right FPS is very important.
(but imho more to avoid blended frames then for syncing...)

[Job ter Burg] "Anyway. I don’t think we’re in disagreement."

Me neither, just trying to educate the masses, not you ☺
(And avoid doing actual work...)

Bouke
http://www.videotoolshed.com


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Job ter Burg
Re: Video is 23.98 fps on Red and Audio was recorded at 24 fps 48K
on Apr 18, 2018 at 6:36:57 pm

[quote]The audio is in fact recorded as 48000Hz, but flagged as if it was recorded at 48048.[/quote]I beg to differ. In traditional 24fps shoot with 23.976/29.97 post situations, a film camera would run 24.0000fps and sound would be recorded to a 48048 clock, and played back to a 48000 clock. Avoiding sample rate conversion. Frame stays a frame (picture), sample stays a sample (sound).

Sure, you can restamp and use that to pull up or pull down, but that's not what I was referring to.


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Job ter Burg
Re: Video is 23.98 fps on Red and Audio was recorded at 24 fps 48K
on Apr 18, 2018 at 6:41:44 pm

[quote]If you see the framecounter go from 23 to 00, of course it can be 23.976 as well as 24, so this is relative meaningles.[/quote]
Exactly.

[quote]the metadata inside the clip will tell you shooting rate[/quote]
Assuming the clip has that metadata. 35mm film would not be able to tell you if it was shot at 23.976 or 24.
Also, you are confirming my point: you'll need to find out the speed the camera ran.


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Job ter Burg
Re: Video is 23.98 fps on Red and Audio was recorded at 24 fps 48K
on Apr 18, 2018 at 6:45:50 pm

https://www.sounddevices.com/tech-notes/file-format-overview
Because most SD and HD video formats use a 48 kHz sampling rate for their native audio formats, sound files are generally recorded at 48 kHz. Nonetheless, there are numerous exceptions to the 48 kHz rule.

In NTSC-land, one exception is the sampling rate of 48048 Hz (48.048 kHz), 0.1% greater than 48 kHz. It is used in select applications when film or video is shot at true 30 or 24 frames and is pulled down to 29.97 or 23.98 in post. When those 48.048 sound files are played back at 48 kHz, the 0.1% pull down will be achieved without additional sample rate conversion.


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Bouke Vahl
Re: Video is 23.98 fps on Red and Audio was recorded at 24 fps 48K
on Apr 19, 2018 at 6:56:13 am

[Job ter Burg] "When those 48.048 sound files are played back at 48 kHz, the 0.1% pull down"

If this is the case, I stand corrected of course.
Do you happen to have one of those files to study? (Just for hobby, I very much doubt this is still used nowadays.)
Both samplerate and byterate should reflect 48048.
Of course there is no way for me to check what is really happening unless there is tone that should be at a very exact frequency, but still, it's fun. (Yes, I am a nerd.)

Bouke
http://www.videotoolshed.com


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Brent Marginet
Re: Video is 23.98 fps on Red and Audio was recorded at 24 fps 48K
on Apr 16, 2018 at 4:30:34 am

If you do run into the situation where the Audio is drifting out of sync with the Video this is what I have done in the past. Use ProTools to do a Sample Rate Conversion from 24 to 23.976fps.

The nice thing about doing it with PT is that it creates new files in it’s Audio Folder so none of the original files are modified in any way. Secondly you can do a batch conversion. The one real negative to this process is that the T/C will be offset from the original T/C.

"MY MEDIA/PROJECT MOTTO: If you think three copies of your Media or Projects are enough. Take a moment to place a value on them and then maybe add two more. Hard Drives are now stupidly cheap. A RE-SHOOT AND YOUR TIME AREN'T."


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Michael Phillips
Re: Video is 23.98 fps on Red and Audio was recorded at 24 fps 48K
on Apr 24, 2018 at 3:09:30 pm

You can also open a copy of the files in Wave Agent and set sample rate to 47.952 and it will get pulled down upon import. See my spreadsheet for these types of modifications:

http://24p.com/wordpress/?p=195


Michael


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