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  #1  
Old 08-29-2011, 02:32 PM
SZE SZE is offline
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Default 24p - 23.976 fps video & 24 fps audio

Hi

I am starting the sound edit on a film shot on the Canon 5D. The film was shot at video speed 23.976 fps, with the sound shot seperately at 24 fps.

As the Canon 5D has no way of receiving external TC or audio feeds (from what I understand), sound has to be re-sync in post using the clapperboard.

I have been brought onto the project at a stage when the sound rushes have already been loaded into Final Cut Pro 7, and sync up to clapperboard and the reference audio there is from the Canon 5D built-in mic.

The problem picture department are having (I am yet to receive any material) is that the sound rushes start off in sync, but slowly start to drift out of sync (running longer), to a degree that after 5 minutes or so you are looking at over 2 frames difference.

I am assuming that at the stage the sound rushes were imported into Final Cut Pro some kind of automatic pull-up / pull-down should have been carried out, but unfortunately it hasn't so this will need to be fixed by us in sound post.

I would be very grateful if anyone can give me a quick breakdown of the usual 24p HD workflow, and if anyone has ny suggestions about how the 24 fps sound rushes can be fixed, and hopefully automatically converted/processed upon import into Pro Tools HD.

Thanks in advance
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  #2  
Old 08-29-2011, 03:21 PM
Postman Postman is offline
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Default Re: 24p - 23.976 fps video & 24 fps audio

Quote:
I am assuming that at the stage the sound rushes were imported into Final Cut Pro some kind of automatic pull-up / pull-down should have been carried out, but unfortunately it hasn't so this will need to be fixed by us in sound post.
Maybe, but based on what you said I don't think that is the problem. If this were a "video speed" vs. "film speed" issue, the amount of drift would be much larger, around 7 frames in 5 minutes, not 2 frames in 5 minutes. If the audio recorder was not actually sychronized to the camera on set, it is possible for such a drift to occur. That is a big drift for modern equipment, but not outside the realm of possible.

One way to deal with it is to make edits in the audio, either snipping out tiny bits or adding tiny bits on a regular basis, every 30 seconds to a minute. If the material does not allow that, like a musical performance, then you'll have to find the correct amount of speed change/pitch change for a longer take, either by experimentation or with a calculator.
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  #3  
Old 08-30-2011, 01:09 AM
Frank Kruse Frank Kruse is offline
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Default Re: 24p - 23.976 fps video & 24 fps audio

Quote:
Originally Posted by SZE View Post
Hi

I am starting the sound edit on a film shot on the Canon 5D. The film was shot at video speed 23.976 fps, with the sound shot seperately at 24 fps.

As the Canon 5D has no way of receiving external TC or audio feeds (from what I understand), sound has to be re-sync in post using the clapperboard.

I have been brought onto the project at a stage when the sound rushes have already been loaded into Final Cut Pro 7, and sync up to clapperboard and the reference audio there is from the Canon 5D built-in mic.

The problem picture department are having (I am yet to receive any material) is that the sound rushes start off in sync, but slowly start to drift out of sync (running longer), to a degree that after 5 minutes or so you are looking at over 2 frames difference.

I am assuming that at the stage the sound rushes were imported into Final Cut Pro some kind of automatic pull-up / pull-down should have been carried out, but unfortunately it hasn't so this will need to be fixed by us in sound post.

I would be very grateful if anyone can give me a quick breakdown of the usual 24p HD workflow, and if anyone has ny suggestions about how the 24 fps sound rushes can be fixed, and hopefully automatically converted/processed upon import into Pro Tools HD.

Thanks in advance
You are mixing up TC and playback speed. Digital sound is always recorded at 100% speed not a frame rate. Sound speed is set by the sample rate not the TC rate.
The sound is drifting because of the FC"P" 24fps bug (which apple calls a "feature").
Read the sticky about the FC"P" bug.
Your sound files are just fine since they were recorded at 100% speed and 23.98 if your reference. You only used the wrong TC so FC"P" thinks it has to pull down the audio.
It´s a simple play-back issue.
Try this: Ask them to give you a shot with clapper board at original speed (23.976). Import the video into PT. Import the sound to PT as well (don´t apply any SRC!!). Make sure neither the video nor the audio pull-down is on. Line up the audio. I´d make a bet that they will run in sync just fine.
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  #4  
Old 08-30-2011, 05:25 AM
Postman Postman is offline
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Default Re: 24p - 23.976 fps video & 24 fps audio

I thought it was the FCP bug at first but the amount of sync drift SZE reports, 2 frames in 5 minutes, is much too small for it to be caused by the FCP bug. That would be 7.2 frames each 5 minutes.
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  #5  
Old 08-30-2011, 09:24 AM
SZE SZE is offline
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Default Re: 24p - 23.976 fps video & 24 fps audio

Thanks both for your replies. Having read into this a little more, I am starting to also think that this is a simple case of no master tc device being on set to keep camera, sound equipment, etc. in perfect lock. So we'll just have to re-sync manually where necessary.

I will definitely read up on the FCP bug though also, as it sounds like something to be aware about.

Thanks again.
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  #6  
Old 08-30-2011, 09:51 AM
HD2 HD2 is offline
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Default Re: 24p - 23.976 fps video & 24 fps audio

Quote:
Originally Posted by SZE View Post
Thanks both for your replies. Having read into this a little more, I am starting to also think that this is a simple case of no master tc device being on set to keep camera, sound equipment, etc. in perfect lock. So we'll just have to re-sync manually where necessary.

I will definitely read up on the FCP bug though also, as it sounds like something to be aware about.

Thanks again.
Read Frank's reply again. You mis-understand the relationship between TC and speed. TC is just an address of a given position on the sound file. It does not affect the speed of the file, that is regulated by the sample rate it was recorded at and then the sample rate it is being played back at.
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  #7  
Old 08-30-2011, 10:25 AM
Craig F Craig F is offline
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Default Re: 24p - 23.976 fps video & 24 fps audio

I heard reports that the frame rate of the D5 can fluctuate and what was the audio recorder is may have fluctuated as well
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  #8  
Old 08-31-2011, 01:42 AM
SZE SZE is offline
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Default Re: 24p - 23.976 fps video & 24 fps audio

Thanks everyone.

Yes, I understand now that the FPS and the speed of the recording are two different things.

As Postman mentioned the drift here is small - I am not seeing a 0.1% speed difference that you would expect to see with a 23.976 / 24 fps mismatch. It is more like 0.02% or something like that.

Interesting point about the potential clock problems with the 5D - we are talking about a stills camera at the end of the day...

On a more general note, what is the usual workflow on a 24p project? I have just received a test video @ 23.976 fps - so I run my Pro Tools session @ 23.976 fps? At some point pic. editorial will need to do the change to 24 fps for the cinema release (DCP & 35mm prints are to be done), and I would prefer for them not to do the sound speed change...

How do people normally deal with this?

Thanks again in advance
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  #9  
Old 08-31-2011, 02:19 AM
Frank Kruse Frank Kruse is offline
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Default Re: 24p - 23.976 fps video & 24 fps audio

Quote:
Originally Posted by SZE View Post
On a more general note, what is the usual workflow on a 24p project? I have just received a test video @ 23.976 fps - so I run my Pro Tools session @ 23.976 fps? At some point pic. editorial will need to do the change to 24 fps for the cinema release (DCP & 35mm prints are to be done), and I would prefer for them not to do the sound speed change...

How do people normally deal with this?

Thanks again in advance
real 24P would be shot at 24.00fps.
for 23.976 I usually do the entire edit and mix at 23.98 (no pull ups). As the final process I´d pull up the master to 24P and deliver 24.00@48k
pretty easy.

Over here we shoot at 24.00 unless there´s some US based vfx house involved. For some reason they prefer 23.98.

Even when you shoot 24P it´s still easy to output 29.97 DVDs if someone wants an NTSC dvd or tape.

IMO way easier than do the whole show at 23.98 only because 1 or two people might want a NTSC VHS tape for dailies ;-)
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  #10  
Old 08-31-2011, 08:29 AM
tom_lowe tom_lowe is offline
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Default Re: 24p - 23.976 fps video & 24 fps audio

Quote:
Originally Posted by Frank Kruse View Post
real 24P would be shot at 24.00fps.
for 23.976 I usually do the entire edit and mix at 23.98 (no pull ups). As the final process I´d pull up the master to 24P and deliver 24.00@48k
pretty easy.

Over here we shoot at 24.00 unless there´s some US based vfx house involved. For some reason they prefer 23.98.

Even when you shoot 24P it´s still easy to output 29.97 DVDs if someone wants an NTSC dvd or tape.

IMO way easier than do the whole show at 23.98 only because 1 or two people might want a NTSC VHS tape for dailies ;-)
It's not just used for NTSC dailies, it's used because lots of TVs only suport 60i and it's a nice convenient way of handling a near 24P signal without any conversion down the line. Even so-called 24P compatible displays and projectors are actually 23.98.
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