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Audio synch issue - 24 bit/16 bit and 23.97 fps and 24 fps ?

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Shawn Kornhauser
Audio synch issue - 24 bit/16 bit and 23.97 fps and 24 fps ?
on Jul 2, 2017 at 9:23:24 pm

Hi

I'm a fairly new Premiere Pro user (converting over from FCP) and I'm having some trouble syncing audio.

It was a two camera shoot.

Everything has 48 khz audio

Cam 1: 16 bit audio and 23.967 fps
Cam 2: 24 bit audio and 24 fps

I always assumed 23.967 and 24 are the same for practical purposes, but wasn't sure if that could be an issue.

Any suggestions?

Thanks


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John Pale
Re: Audio synch issue - 24 bit/16 bit and 23.97 fps and 24 fps ?
on Jul 3, 2017 at 4:07:55 am

No, they are not the same.

You can try to right click/modify/interpret footage on the 24 fps camera. Change the frame rate to 23.976. This will play the all the frames at the new rate with no interpolation. This needs to be done before you edit with the clips.

The 24 bit/16 bit difference isn't an issue.


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Brent Marginet
Re: Audio synch issue - 24 bit/16 bit and 23.97 fps and 24 fps ?
on Jul 3, 2017 at 6:55:11 am

This will definetly cause some issues.
First off, if 23.976 and 24fps were the same then they wouldn't have different FPS numbers just like 29.97 and 30fps. I apologize for this but if a Car and a Truck where the same then they wouldn't have different names.

Here's a couple examples of the difference.
First with 1 and then 10 hours of footage.
This should clear things up for you.

1 hour of footage. 24x60x60 or 86400 Frames @ 24fps.
FPS Frames played back in 1 hour. Time to Playback 86400 Frames.
23.976 86314 1:00:03:14
24 86400 1:00:00:00

10 hours of footage. 10x24x60x60 or 864000 Frames @ 24fps.
FPS Frames played back in 1 hour. Time to Playback 86400 Frames.
23.976 863136 10:00:36:00
24 864000 10:00:00:00

Now it becomes pretty evident especially with a 10 Hour Video why things will go out of sync. So you can see why your Audio will not sync with both Cameras. Your A-Cam is running 0.1% slower or 24 x 0.999 = 23.976fps than the B-Cam. Even if you jammed the T/C on the Cameras the Time Code for the exact same moment in time on the two Cameras will not be the same and drift farther apart as the day goes on. A good example would be an A/B-Cam common slate.

There are a few ways to fix this if Interpreting the 24fps footage as 23.976 doesn't work. That would require a mini novel to explain unless I were provided with exact details.

Was the Audio only recorded as Split Audio in the Cameras or was there an External Recoder. What Frame Rate was the external recoder set to and what Frame Rate do you intend on cutting in. The Frame Rate you cut in will also be determined by what your final destination(s) for this Video are. Internet, Computer Playback and BlueRay can do both but if there's a Broadcast Deliverable then you must cut at 23.976 to do the proper 2:3 conversion to 29.97.

"MY MEDIA MOTO: If you think three copies of your media is enough.
Take a moment to place a value on it and then maybe add two more.
Hard Drives are now stupidly cheap. A RE-SHOOT AND YOUR TIME AREN'T."


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Robert Withers
Re: Audio synch issue - 24 bit/16 bit and 23.97 fps and 24 fps ?
on Jul 3, 2017 at 3:26:10 pm

Thanks for the info, Brent. Do I understand that the 23.976 rate is for broadcast deliverable programs and that's why it exists? To convert to 27.97 fps for broadcast.
I've been wondering why it exists.
It seems DCP conversion studios for theatrical projection mostly require 24 fps.
Thanks for any further light you can shed on this.
Best,
Robert

Robert Withers

Independent/personal/avant-garde cinema, New York City


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Robert Withers
Re: Audio synch issue - 24 bit/16 bit and 23.97 fps and 24 fps ?
on Jul 3, 2017 at 3:31:07 pm

Typo: should be 29.97 fps for broadcast.

Robert Withers

Independent/personal/avant-garde cinema, New York City


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Dave LaRonde
Re: Audio synch issue - 24 bit/16 bit and 23.97 fps and 24 fps ?
on Jul 3, 2017 at 4:24:34 pm

[Robert Withers] "Do I understand that the 23.976 rate is for broadcast deliverable programs and that's why it exists? To convert to 29.97 fps for broadcast."

That would be correct. Think of it as the NTSC Film Frame Rate.
When color TV was introduced in the USA in 1953, they had to make it compatible with existing B&W sets. And in order to make it a color signal, they needed to transmit a tiny bit more information. They were limited to changing the frame rate to accommodate the extra info, so they did -- from 30 fps to 29.97 fps.

I never understood why they didn't change it back to 30 fps when TV broadcasting went digital. It would have been the perfect time.

Dave LaRonde
Promotion Producer
KGAN (CBS) & KFXA (Fox) Cedar Rapids, IA


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Robert Withers
Re: Audio synch issue - 24 bit/16 bit and 23.97 fps and 24 fps ?
on Jul 3, 2017 at 5:16:41 pm

Thanks Dave. I had heard about the reason for the change to 29.97 so I guess this has filtered down to digital capture in the form of 23.976. And we need to shoot 24 fps for theatrical and 23.976 for broadcast.
A friend shot both film and video and edited in FCP7 which identified the footage as 23.976. Maybe interpreted the scan as 23.976. She had sync issues in doing the mix.
I'm using Premiere which lets you make the choice -- now I know which to choose for what.
Thanks again,
Robert

Robert Withers

Independent/personal/avant-garde cinema, New York City


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Brent Marginet
Re: Audio synch issue - 24 bit/16 bit and 23.97 fps and 24 fps ?
on Jul 4, 2017 at 1:48:33 am

23.976 with a 2:3 pull up gives us 29.97fps just like 24 with a 2:3 pull up gives us 30fps.
So exactly 6 frames per second are added to get from one to the other.

In our digital world we can shoot everything at 23.976 and that will give us the most delivery possibilities.
23.976 can be converted to 24fps with a 0.1001001001...% Pull Up and to 25fps with a 4.1666666666...% Pull up.
Of course if you A/B a 23.976 and 25fps Video with the pull up the Audio will have a slight chipmunk sound to it.

The solution to the Video/Film problem is to shoot the Video at 24fps as well.
If it wasn't and your NLE is not able to interpret the footage as another Frame Rate then either the Video needs to be speed up to 24fps or the Film needs to be Telecine'd down to 23.976. Which way you need to go is determined by the Frame Rate the Audio was Recored at.

Dave explained the reason for 29.97 very well in a condensed way.
Here's a link that explains it in more detail.

http://glydeck.blogspot.ca/2011/07/why-do-we-have-2997-frame-rates-and-not....

If we wouldn't have rushed Colour to the Market to get ahead of everyone else these problems and a lot of pain and suffering could have been avoided. The Europeans looked at all of our mistakes, yes there were quite a few and fixed them before bringing there Colour System to market. That's why they do not have some stupid Frame Rate like say 24.975 although there is a so called Slow Pal but that will be left for another article.

"MY MEDIA MOTO: If you think three copies of your media is enough.
Take a moment to place a value on it and then maybe add two more.
Hard Drives are now stupidly cheap. A RE-SHOOT AND YOUR TIME AREN'T."


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Shawn Kornhauser
Re: Audio synch issue - 24 bit/16 bit and 23.97 fps and 24 fps ?
on Jul 3, 2017 at 3:50:57 pm

Thank you for the helpful post, Brent. I don't consider myself especially knowledgeable when it comes to the intricacies of formats, codecs, and other elements that are important for an editor to know - so the simplistic explanation is appropriate here ☺

Some answers to your questions:

1. Audio was recorded separately using a Zoom H4N recorder. The frame rate is listed at 48000 Hz. Is that what you're looking for?

2. It looks like an issue I am having is that I am trying to edit with proxy files for the majority of my footage. The DP I had shooting the majority of my footage was shooting on an Alexa as well as another camera (can't recall) that my machine can't really edit at full quality. The proxies are at 24 fps 720p and the full quality clips come in as 23.967 fps and either 1080p or 4k. So I'm guessing I want everything at 23.967

This feels like a ton of variables and I'm not totally sure how to edit with proxies, make sure all of my timelines are set properly for the final conversion to full quality, mix different footage without screwing myself over down the road, have audio be synched, etc.

Should I be hiring someone to walk me through this? I'd certainly prefer to hire a professional editor but I can't afford it at the moment.

Thanks again (to you also John).

Shawn


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Brent Marginet
Re: Audio synch issue - 24 bit/16 bit and 23.97 fps and 24 fps ?
on Jul 4, 2017 at 1:13:01 am

48000HZ is not a Frame Rate it is your Sample Rate. The Zoom does not Jam to or Output T/C so the only way there would be a set Time Code Frame Rate is if you set it to one before recording.

In your second point you mention that the Proxies are 24fps but the original footage is 23.976 so first thing would be to make sure that your proxies are the same Frame Rate as the Original Footage is. This is what's causing all of your grief. You may have to delete all of the Proxies before changing the Premiere Proxy settings to 23.976. You may then be able to solve all of you're issues because now it sounds like both of the Cameras were set to 23.976 but for some reason the Proxies on the one Cam are being built at 24fps.

I can't see why you would need to hire someone, just fix your Proxy problem.

Note: if the file extension of that second camera is .R3D then it was a RED Camera if it is .MXF then it could be any number of Cameras including Sony, Canon, etc. Install a little app called MediaInfo it can tell you a lot about your media and is available in the Apple App Store for free or can be downloaded for Windows directly for the creators site. That's MediaInfo and not Media Info.

"MY MEDIA MOTO: If you think three copies of your media is enough.
Take a moment to place a value on it and then maybe add two more.
Hard Drives are now stupidly cheap. A RE-SHOOT AND YOUR TIME AREN'T."


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