VideoHub 12x12 Same as Physical Patching?

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NickDub

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VideoHub 12x12 Same as Physical Patching?

PostMon Oct 18, 2021 7:36 pm

I've seen this happen a few times, and it is now leading me to believe that the BlackMagic Design VideoHub 12x12 doesn't re-clock and signal-boost for every output on their non-clean switch model.

Situation 1:
This weekend, I was running a larger show where all 12 outputs of my video hub were needed, with 4 of those outputs displaying the same input, routed to different areas: Broadcast, Record, TV Chain, and Projector Chain. The projector and TV chains each had their own SDI 1x8 Distribution mini-converter. The strange thing is, when everything was connected, the 2 projectors (and their 1x8 distro) lost their signal. To test, I began by swapping the mini-converters, and it quickly became apparent that in any config, the projectors worked just fine whenever the TV distros were unplugged. As soon as the chain on the TV end was extended, the projectors went out again.

This leads me to think that despite being connected to different outputs on the VideoHub, electronically both were essentially daisy-chained or "t-connector" split.

Situation 2:
An install I've spent a lot of time in uses a SmartVideohub to send 2 MEs and 4 Auxes to various displays around the building. I don't have any idea what the wiring looks like beyond the hub, but I have had random signal dropouts if I send the same output to too many destinations at the same time. As a workaround, I have set one of the auxes to follow program output within the upstream switch, so that I have a 2nd source to use whenever we reach a threshold when dropouts become a problem.

My question is twofold. First, am I correct in assuming that outputs patched to the same input are essentially "patched" together, and second, is this still the case on the newer, Clean Switch edition of the VideoHub family?
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Dave Del Vecchio

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Re: VideoHub 12x12 Same as Physical Patching?

PostTue Oct 19, 2021 5:46 am

According to the specifications page, the VideoHub 12x12 includes SDI reclocking on all SDI outputs:
https://www.blackmagicdesign.com/produc ... s/W-VHS-01

The main difference with the VideoHub CleanSwitch model is how it handles the inputs (as the outputs are reclocked on both models). The CleanSwitch model has frame synchronizers on the input signals (a bit similar to what is included on the ATEM switchers). This allows for cleanly switching between video signals sent through the VideoHub CleanSwitch without any tearing or other artifacts. This does add a latency of up to 1 frame in order to synchronize the switching of signals to frame boundaries.

As for the problems you are seeing, I would guess that it may have something to do with the cables being used, length of the cables being run, or type of cable used. Or perhaps some type of ground loop or other SDI grounding issue.

If possible, you might try experimenting with a more controlled configuration where you control everything in the signal chain and can better narrow down which connection or piece of equipment is causing the problem.

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