Audio and frame rate sync.

Blade Borge

Blade Borge

Well-known member
Sound Newb here, let's say video and audio are being recorded separately but will be combined later to be in sync. Does it matter if I'm filming in 23.97 or 29.98 fps in order to have proper sync? Is there a button or something on audio recorders that designates whether it's going between 24 or 30 frames?
 
Only stating this because you actually said it...

24 and 30 are different than 23.976 and 29.97 please be aware of that.

For the most part people will be shooting at either 23.976 or 29.97 and not 24 or 30.

(some cameras even at 24p do the pull down in camera to 29.97, so be aware of what your camera does)


I doubt you will doing telecine with any of your projects (let us know if thats your intent)
so if you will be sync'ing in your timeline its easiest and best to use the same timecode on camera as it is on the audio recorder.

That being said both of those time codes are able to be mixed, so the reason to use the correct ones would come into play when sync'ing via timecode.

If you are strictly going to sync using a clap (slate or otherwise) it wont be a big deal.

Most pro audio recorders can switch between all the frame rates you would need including ones to help in pull down in telecine.
 
As a general not I would say check the stickies because a lot of stuff like this is covered up there.

Sound does not use or care about frame rates, only speed. As long as everything stays at the same speed your fine.

OK what does that mean???

Well you can shoot at any of those frame rates and as long as you don't change the speed of the footage then it plays back in "real time".

If you record sound and you don't change it's speed then it will also playback in "real time".

If both play back in real time you good. Well good with a *. THe * is that if either device has a not to great clock then they may only be close to "real time". Generally on takes under ten minutes or so you don't have to worry about the clock "drift". As always YMMD.

Back to the story...

The classic problem with film was it was shot on film and then edited on video. So the speed was slowed down a small amount in that conversion and you had to then also slow down the sound so they would stay in sync.

Your shooting video and staying in video (a guess) so unless you do something wanky like shoot at a true 24.0 and then switch to 23.98 you should be fine. If you shot at 24.0 and stayed at 24.0 you would still be OK, well until you tried to play it on a TV.

IF you end up changing your frame rate that's when you can get into trouble.

THe only time frame rates come into it in sound are when you are using Time Code and then they have nothing to do with the speed of the recording, it's just a way to find a position. If your not trying to sync to a tape deck you can pretty much forget about TC these days because it's just a time stamp at the head of your file.
 
Scott, just going to add this for the OP, not you because I know you know this..

If your audio file is timecode stamped with say a 30ND code and you drop that into a video edit time line thats 29.97
a "certain" edit program would slow down your 30ND file to 29.97 making it now run slower than it was originally recorded.

I don't know if this has since been fixed but its wise to have your timecode stamps "correct".

The less expensive recorders out there that don't have time code built into them makes it so you wont have to worry about a problem like that.
If you use a recorder that does have timecode, even if you aren't using the time code to sync, its still wise to get your stamps correct.
 
Blade Borge said:
Sound Newb here, let's say video and audio are being recorded separately but will be combined later to be in sync. Does it matter if I'm filming in 23.97 or 29.98 fps in order to have proper sync? Is there a button or something on audio recorders that designates whether it's going between 24 or 30 frames?
Click to expand...

The 'buttons' you need to press on an external recorder, are 'select 48k' digitizing rate, '24 bits' (or at least '16 bits'...), and synchronize the sound to the film, via the use of the clapper, just like in the movies, and then in the NLE lining up the clapper audio 'mark' with the video frame where the clapper comes together.

The ritual of marking includes calling out the shot information so it is captured on the audio, and updating the slate with correct shot information, so that in the NLE you can get the
right chunk of video with the right chunk of audio.
 
Having dealt with audio from production all the way through post, I can say that making sure your camera and audio recorder are running at the same frame rate is really important. If that stuff is off, you won't be able to just spot the audio into a session and have everything line up like it should.

In terms of running timecode on production, this is what I have always recommended, and people that didn't listen to me (we're talking big budget tv and film) have had problems.

1: Have a master timecode generator on set. This is the King of timecode. Set it to time of day. With date at the beginning.
2: Jam your slates, audio recorders , lockit boxes, and cameras to this master timecode generator in the morning, and after lunch.

Again. It is absolutely essential that everyone is on the same page in terms of framerate. If the camera is at 29.97, and the audio recorder is at 30, you are screwed in post unless you know some tricks to fix it, but even then you have to know what you are doing, or you can screw yourself even further.

Clerks II is a prime example. Camera department told the sound mixer they were running at one framerate, when they were running at something else. First couple of days of dailies are out of sync and they can't figure out why until I get the call from the sound mixer (this is back in my Coffey Sound days) about the issue. I go to set, and bring the Ambient master timecode generator. I go around to camera and audio and figure out the problem in about 5 minutes. So, they had several days of dailies NOT in sync. Thankfully there is a program out there called "soundhack" that allowed me to change the metadata of the audio to conform to the picture, essentially letting me change the framerate of the audio, and it worked.

On the mocap for Uncharted: Drake's Fortune, I had a master timecode generator, and everything was hard lined to that generator. I was running a Deva V and they were running about 4 to 5 video decks. I handed them off the audio files, and they dropped them right into FCP and, blammo, they lined up perfectly with no issues.
 
Blade Borge said:
Is there a button or something on audio recorders that designates whether it's going between 24 or 30 frames?
Click to expand...

Considering this is a pretty general question, I think we've missed something here. Not every audio recorder utilizes TC. You need to know what you're working with. None of the hand-held recorders use TC. The FR2-LE does not. I don't believe the Roland R-44 does (you have to get the R4-Pro for that).

The most crucial settings are sample rate and bit-depth. Audio for video and film primarily runs at 48kHz. 16-bit is the typical bit depth for distribution, but 24-bit is better for acquisition. So whether or not your recorder uses TC, make sure you're recording at 48kHz/24-bit.

If you have a recorder that does utilize TC (TASCAM HD-P2, Fostex FR2 with TC card installed, Roland R4-Pro, SD 702T or 744T, etc.), then you do need to match frame rate to the camera. If for no other reasons, because it's the right thing to do and because it will save post (as already mentioned) a thousand headaches.
 
Thanks for all the informative feedback guys, truly blessed to be around such smart folks. So, set to 48k, 24 bits, if it has framerate controls stay on it exactly, not 30 when it's 29.97, etc. Thanks for the tips Dave, I wish I had a master tc generator, someday though. And so if the recorder doesn't have tc/framerate setting control I should probably be okay if I stick with the 48k, 24 bits?
 
Make sure you use a clap slate. That will help you line things up if you aren't using TC to spot audio into your sessions. Even if you have TC, you should use a clap slate just as a safety.
 
davefisk said:
Having dealt with audio from production all the way through post, I can say that making sure your camera and audio recorder are running at the same frame rate is really important. ....
Click to expand...

Dave, this is important ONLY if you are using TC to sync your sound to picture. And it still has nothing to do with the sound "drift" only where it starts relative to picture.

So I think you are spot on with that workflow but it confuses maters a bit since the OP is not using that work flow.

It's one of the tricky parts of this forum, figuring out which correct advice to give. It's the appropriate VS accurate conundrum.

I fall in to the trap also, though I'm getting better.
 
Rippie said:
... a "certain" edit program would slow down your 30ND file to 29.97 making it now run slower than it was originally recorded.

I don't know if this has since been fixed but its wise to have your timecode stamps "correct".
Click to expand...

As far as I know that "certain" program still has the same issue. ;~)

good catch almost forgot that one.
 
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