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Technical explanation on genlock

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Luc Renambot
Technical explanation on genlock
on Jun 15, 2011 at 3:44:08 pm

Hi,

Could someone explain me (or send me a link) what happens when genlocking HD-SDI signals ?
What is sent over the wire from a sync-generator (like the BM Converter Sync Generator with 6 outputs) ?

How does it work when using one source as sync source (master) ?
I could see that the devices sync on the same front of a signal (front or back porch), but how does it related to making sure devices are showing the same frame (and not off by one or several frames) ? Would time-codes sync the frames ?

context: I'm thinking of syncing a large number of sources (~ 40) and trying to understand how it works and how to implement it.

Thanks for any pointers.

Luc


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Bob Zelin
Re: Technical explanation on genlock
on Jun 16, 2011 at 3:41:12 am

new invention on the computer - and it's really amazing-
its called GOOGLE

http://en.wikipedia.org/wiki/Genlock



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Luc Renambot
Re: Technical explanation on genlock
on Jun 16, 2011 at 3:58:30 am

So cool ;-((


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Margus Voll
Re: Technical explanation on genlock
on Jun 16, 2011 at 6:11:28 am

General idea is the same as with few sources. Genlock sync signal is reference for everybody connected to it. Different question is what devices should you use. Frames should be in sync if from cameras as they feed realtime picture. VTR's on other hand are controlled by some sort of controller that plays the exact frame that any other player controlled by this controller.

This is how i have get it. Maybe i'm mistaken and get some beating from Bob but thats ok for me :)

If from anyone, then he is the guy you will want to get beating from if you want to know anything

--

Margus

http://iconstudios.eu


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Gary Adams
Re: Technical explanation on genlock
on Jun 21, 2011 at 9:52:25 pm

Back in my day which probably precedes just about everyone else’s day, all video sources had to be synchronous or they simply could not be used in a vision mixer type of device. With most modern effects type switchers having frame synchronizers, this is not totally necessary, however it is worth considering the side effects. Frame synchronizers will delay the incoming signal anywhere from their minimum to a full frame and this will continuously vary as the source sync drifts. Some people might notice the fact audio may get out of sync when this happens. Another side effect given all sources are slowly drifting about in time and the frame sync can only hold a frame of delay, when full, the buffer memory must drop back a field or frame causing a loss or jump in the image. It doesn’t happen very often but will happen. I may be the only one that can see it. All sources, camera and tape alike would do the same thing. So, if it is feasible, it is always best to lock all the devices.


Gary

Gary Adams
DaVinci Revival Product Manager
Blackmagic Design


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