synching audio and video: 23.98fps

[wildplum]

I will be doing the audio recording for a DVD shoot. I have done a little of this type of thing before, but this is my first HD shoot. In the past I have found that synching to a house master generater is the best way to go. No separate master gen for this shoot. I have had problems synching to camera SMPTE output because the camera often shuts down (to change batteries, tape, whatever), so i have recommended that i provide SMPTE and the cameras synch to me. I am using DA-78's to record (also locking to a Protools LE system) and provide SMPTE (the DA-78 provides for a variety of frame rates, but not 23.98). so, i recommened this to the video guys and they said ok. i will be the time code master and send one of their cameras a time code feed, then they will "jam synch" their other cameras.

(what is a good definition of "jam synch" for a video challenaged audio guy?)

so, far, so good (quoteing the guy who jumped from the 14th floor, as he passed the 12th floor). now the kicker.


they run the cameras at 23.98fps. My DA-78's do not support this new frame rate. i read somewhere that i could feed them 29.97nondrop, but this doesn't seem right to me. how does one handle this sort of thing? should i tell them they have to find the budget to rent a house master synch device? or is there some way for me to send them SMPTE or for them to send me TC? The shoot is for a for 90 minute music set, so drift over time would seem to be an important issue.

[huub]

welll... If your da78 doesnt support 23.98, youre kind of screwed I guess..
You could hire a tc generator and record tc on an audiotrack.. TC generators need video ref though..
Are there devices that generate both video blackburst and tc?

On eng multicamera shoots I have used these wireless tc devices that give all cams and multitrack tc..
Were brought by camera people so don't know brand and type..

Oh, and jam sync means feeding tc once, and then letting the cameras run free.. This means a little bit of drift, unless the cameras are getting video ref from the same device as the tc generator.. a little drift is no big issue in music though, they tend to edit per song anyway, and cut out the bits where nothing is happening, most eng multicam is done with jam sync and thus drift..

[dirkjan]

Hmmm, a framerate of 23.98? The only ones I've heard of are:

• 24 frame/s (film)
• 25 frame/s (PAL colour television)
• 29.97 (30*1.000/1.001) frame/s (NTSC color tv)
• 30 frame/s (American b&w tv) (virtually obsolete)

Is this not a 24 fps framerate, running -0,1%?

Maybe a synchronizer can help you.
For example the Motu Timepiece AV. It has a mode ('frame lock' = off) in which it autosyncs to the incoming TC and can detect that more than 5 frames in a row are missing. If this is the case it starts performing a 'psuedo jam sync', resyncing to the incoming TC-signal when it comes back without jumps in the TC signal of your DA-78.

[Karl_Lohninger]

I wouldn't worry,
run 29.97 (non-drop), make sure the editor knows about it. In 99.99999% of all cases this works perfectly fine - done it so often - never had a problem.

best, Karl

[Swopes]

I think Karl is correct to run at 29.97nd,

but the real question is what camera are they shooting on. My guess is they're the sonyf900's i most often see them shooting 23.98.

you may wish to take this question to the R.A.M.P.S section of google groups

search for ramps in google groups youll find them.


and Jam-sync also means they have one camera that acts as masters and then they jam (tc out bnc to tc in) each camera off the master.

You could also get sync boxes to handle this for you.

good luck.

P

[wildplum]

Thanks for the information. From what I can gather, 29.97 is the way to go. For reference, the info I got was "we will be recording 720p/23.98fps". The camera is a HPX500 (I assume that is Panasonic) and that rate seems to be its "default". Also, if I understand what I have been told, when running at 23.98 (or 24PN i think it is called), the HPX500 puts out 29.97 at its TC output terminal (BNC). But we decide not to try to synch the audio recorder and the cameras directly.

We have decided that I will take a TC feed from the cameras and record that on a separate track. They will have a stationary camera at the rear of the hall on free run and the HPX500 can continue to gen time code even with the battery or the media removed, so we are good for the length of this concert. Also, I will be sending them a 2-track mix from my position, which they will record onto the stationary camera. This 2-track will give them a reference for synching my audio multitrack in post, should we need it.

The concert is this Friday (22nd). I'll let you know how it goes.