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External TC Sync Accuracy on EPIC 4.0.18

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David Skidmore

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Anyone have any idea if the EPIC syncs at a subframe level... ie 12:34:56 9/10's of a frame on the Lockit equals 12:34:56 9/10's of a frame on the EPIC?

I'm talking with the Lockit attached and feeding TC into the EPIC continuously.

Cheers,
David
 
Only when you also run the camera in Genlock and feed in external sync. I'm not sure what the limit of subframe accuracy is. You have to be able to at least genlock two cameras in order to do 3D, because the shutters and timecode have to be precisely in sync.

What are you trying to accomplish? Is this a sound issue or a picture issue?
 
The sound is ahead of the video by a frame about 60-80% of the time, meaning that we have to manually sync most clips. Just trying to get to the bottom of it and nobody could answer this question. So in theory with genlock, the start of the frame which match precisely with the start of sound's frame as well, yes? With the added benefit that both cameras timing will also match exactly (which we aren't concerned about).
 
Picture clap and sound clap can only ever be sync accurate to the nearest picture frame, as picture is only sampled once per frame. Which means that sometimes they'll coincide exactly, and other times they'll be a frame out, even if Genlock and Timecode are functioning perfectly. When it happens it's usually better to have the picture clap lead the sound clap as in nature light travels faster than sound.

Genlocking two or more cameras will make sure picture frames on each camera start at the same moment though.
 
ericyoung said:
Picture clap and sound clap can only ever be sync accurate to the nearest picture frame, as picture is only sampled once per frame. Which means that sometimes they'll coincide exactly, and other times they'll be a frame out, even if Genlock and Timecode are functioning perfectly. When it happens it's usually better to have the picture clap lead the sound clap as in nature light travels faster than sound.

Genlocking two or more cameras will make sure picture frames on each camera start at the same moment though.
Click to expand...

I just heard back from Red Support/Engineering that Genlock also has the effect of having the picture and sound frame be perfectly in sync, which means we can get very close to 'perfect' sync. :)
 
EPIC, SCARLET, and DRAGON will all sync to a continuously connected timecode source on the crossing of the :00 frame. So that is once per second on the second boundary. As stated by others, adding genlock from the same source device AND putting the sensor sync mode in GENLOCK is needed to keep the sensor timed to the time code. If you are recording audio to an external recorder you also want that to be genlocked if possible.
 
David Skidmore said:
The sound is ahead of the video by a frame about 60-80% of the time, meaning that we have to manually sync most clips. Just trying to get to the bottom of it and nobody could answer this question.
Click to expand...
I always argue that manual sync is trivial and easy. A good assistant editor can check the sync on one clip in about 15 seconds and slide it one way or the other. If you shoot 200 takes a day, that's 50 minutes. It's not a lot of time, and in truth, I would always, always check the clap anyway just to be absolutely sure.

If the sound is consistently about a frame out, then I'd introduce a 1-frame delay in the feed going to camera, which is very easy to do with all pro sound equipment. 33ms is generally what I use for Red, though I tell the clients to only use the Red audio track as a scratch track.
 
Marc Wielage said:
I always argue that manual sync is trivial and easy. A good assistant editor can check the sync on one clip in about 15 seconds and slide it one way or the other. If you shoot 200 takes a day, that's 50 minutes. It's not a lot of time, and in truth, I would always, always check the clap anyway just to be absolutely sure.

If the sound is consistently about a frame out, then I'd introduce a 1-frame delay in the feed going to camera, which is very easy to do with all pro sound equipment. 33ms is generally what I use for Red, though I tell the clients to only use the Red audio track as a scratch track.
Click to expand...

The problem with adding a one frame delay to the sound is that you now go to 20-40% of clips being out versus 60-80%, which I suppose is an improvement but still not ideal. It's probably just easier to use an SB-T and get to the root of the problem, my thinking goes. :)
 
Dave Winder said:
EPIC, SCARLET, and DRAGON will all sync to a continuously connected timecode source on the crossing of the :00 frame. So that is once per second on the second boundary. As stated by others, adding genlock from the same source device AND putting the sensor sync mode in GENLOCK is needed to keep the sensor timed to the time code. If you are recording audio to an external recorder you also want that to be genlocked if possible.
Click to expand...

Lots of people reject the Genlock answer, but that's because they don't understand how the camera reacts differently to a genlocked TC source vs not genlocked. Ultimately, if you don't care about +/- 1 Frame in your Sound Sync, then it doesn't matter. If you do care, then ensure you are getting tc+genlock from sound via an SB-T (or similiar). There's so much debate about it, I had to get to the bottom of it. :)
 
David Skidmore said:
Lots of people reject the Genlock answer, but that's because they don't understand how the camera reacts differently to a genlocked TC source vs not genlocked. Ultimately, if you don't care about +/- 1 Frame in your Sound Sync, then it doesn't matter. If you do care, then ensure you are getting tc+genlock from sound via an SB-T (or similiar). There's so much debate about it, I had to get to the bottom of it. :)
Click to expand...

Interested to know your outcome after trying it with SB-T TC + Genlock. I'm pretty sure it won't change anything, as I said in my previous post, but admit I haven't confirmed myself in a proper test.

[Edit: Reading Dave Winder's linked thread below, Genlock will eliminate one potential source of up to half a frame sync "jitter" i.e. start of picture frame scan and start of Timecode frame in the camera. It still can't eliminate the inherent half frame accuracy between picture and SEPARATE sound unless the sound recorder can sync both timecode AND genlock. Eg. Only the flagship Sound Devices 788T recorder has a Trilevel Sync Word Source capability]
 
You can see some previous explanations in this post: http://www.reduser.net/forum/showthread.php?97688-1-frame-offset-between-slate-and-cam-TC
Time code does not drive the camera timing, but genlock can if you set it up correctly. Sync the camera (sensor sync) and external sound recorder all to the same source. That source could be your sound recorder if it can supply genlock, but TC alone will not do the job. We did extensive tests with a prominent Director's sound guy a while back. With audio feed coming from the sound cart (Zaxcom Deva) and camera genlocked and TC jammed to same source supplying TC to Deva, the scratch track in camera was dead on every time. The track from Deva was off almost every time. Deva can only take TC. I believe Zaxcom has released a firmware update to address this since then, but have not verified that.
 
The plot thickens. So if sound can't provide it genlock, they just need a lockit (and a recorder/tc source that read it)?
 
David Skidmore said:
The plot thickens. So if sound can't provide it genlock, they just need a lockit (and a recorder/tc source that read it)?
Click to expand...
Sound is usually the department that provides an Ambient Lockit or a Denecke SB-T box, jammed from the sound recorder. It's generally $50 a day or less for rental.
 
I never got the Epic to Genlock to a SB-3 in a 25p project.

Tried every setting possible... Could it be that Genlock with the Epic only works in 23.79?

Pat
 
Genlock works at 25p with my Epic with SB-T
 
Just looked up the SB-3 and it does not output Trilevel Sync which is what the Epic requires for genlock. So you need the SB-T.
 
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