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TC out of sync- fostex, deneke, allexa


maxslomoff
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hello,

our mixer is generating timecode from a fostex 824. jamming deneke boxes and slates twice a day. using a 702t as backup recorder. 

 

our video and audio seems to have a 75% out of sync rate, usually just between .25 and 1 frame. 

 

theoretically the deneke boxes should hold perfect sync though. 

 

any ideas what's going on here? 

 

we are syncing dailies with scratch, and slipping audio to match video timecode. wishing the slate clap would sync perfectly every time. 

 

 

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Some clarification is needed. It is not clear what is out of sync with what. Are you syncing the sound from the 702t to the video? Are you syncing the sound from the Fostex 824? Multiple cameras (genlocked?)? Depending on what it is you are syncing, if you use the "clap" of the clap slate to sync up does it work for camera? Do you have all your numbers right --- frame rates, timecode rates, etc. when ingesting into Scratch?

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I'm trying to understand your math? If the "offset" between the Camera timecode, the Timecode Slate and the Production Audio Time Code is .25 to 1 frame - that ain't a problem! That is certainly not a "75% offset".

 

First, several questions;

- What are the TC frame rates of the Alexa, and the Fostex 824?

- What is the TC frame rate of the Denecke slates set to?

-What are the TC Frame Rates of Denecke sync boxes set to?

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How is the Fostex referenced? If there's an issue, I'd just drive the Fostex in external from another Denecke box and see if that solves the problem. 

 

Bear in mind that shutter angle and refresh rates of the on-screen readouts of the slates can cause a 1-frame error in some cases. My line for 20 years in dailies at Technicolor was, "the visible numbers just get us close; the clap makes it exact."

 

How is the 702t getting timecode? Does it produce results that are different from the Fostex? Is the camera getting both genlock reference and timecode, or just timecode? How are the dailies being synced up? There's a lot of factors here that we don't know. 

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we are syncing the mix track recorded on the fostex to the video

the 702T is getting TC from the fostex via hardwire, and is recording a backup mix

the deneke boxes are jamed by the fostex, and then wired to the cameras

the slates are jamed by the fostex

 

all the framerates are right. all gear is set to 23.976fps

 

the cameras are not genlocked

 

we are syncing the clap of the slate, not the numbers on the slate

 

when i say 75% out of sync rate, i mean 75% of the clips are out of sync in this fashion

 

i've heard the deneke box should drift less than 1 frame in 24 hours. i'm not sure if we have a drifting problem, or a tc offset problem though. i've also heard different gear has more or less reliable clocks than others... 

 

can i give you any other info?

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I'm not sure that the fostex has stable timecode. When I used my PD606 I would jam to it of a lockit, and use the lockit as the master.

 

 

I'm betting the Fostex system of stamping a 48.048k file as 48k and automatically bumping the selected TC frame rate by .1% when selecting 48.048 (call "F Mode" by other manufacturers) is the cause.

 

I have a hunch that it is a combination of BWilson's and Glen's suggestions.

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