Adding Genlock

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jawsborne
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Adding Genlock

Post by jawsborne »

Hi guys, I'm in the process of adding genlock to our control room / studio setup and hoping to get a little feedback on my plan.

We run a Tricaster which has built in frame syncs, eliminating the need for genlock, but having those frame syncs turned on creates latency. I'm trying to eliminate as much latency as possible coming out of the Tricaster.

My camera SDI out signal paths go to AJA DAs, then a BlackMagic 40x40 router, then to Tricaster inputs.

I have the AJA GEN10 to generate reference. I'm planning on sending one output of GEN10 to studio, where it would then hit an AJA DA and be dispersed to all cameras reference inputs. Another output of the GEN10 would go to the Tricaster Reference input.

I don't need reference input on my 40x40 router right?

Any apparent issues with my plan?

Thanks!

DaveSt
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Re: Adding Genlock

Post by DaveSt »

I think you are correct. Just lock up all the sources and the Tricaster.

w9wi
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Re: Adding Genlock

Post by w9wi »

Not genlocking the router could lead to "glitchy" routes. Because if you happen to hit the button to change a route at the wrong time, you might interrupt a synchronizing signal.

If you don't plan to change any routes while the destination is live on the air, you may not care.

On the other hand...
- Murphy's Law requires that the worst possible source will always get on the air, whether a human intentionally punched it up or not.
- I'm not familiar with this specific equipment -- I don't know how a Tricaster responds to a sync discontinuity. I've seen some gear exhibit a glitch for as long as two seconds -- you may not be able to put a newly-routed source on air for up to two seconds after a route.
- Looking at the picture of the 40x40 Videohub on the Blackmagic website, it looks like reference has a loopthrough. So all you'd need to genlock the router is a video cable -- if your Aja DA doesn't have enough outputs to send one to the Videohub, you could send the reference to the Tricaster through the router first.
--
Doug Smith W9WI
Pleasant View, TN EM66

jawsborne
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Re: Adding Genlock

Post by jawsborne »

Great thanks guys! and good tip about the router's loop through!

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PID_Stop
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Re: Adding Genlock

Post by PID_Stop »

Just want to add a gentle warning about the tradeoffs of using loopthroughs. My station's original facility used loopthroughs extensively for both reference signals and video signals, and while that certainly reduces the number of distribution amplifiers needed, it can lead to some remarkably non-obvious problems.

If you have to remove a piece of gear in the chain somewhere between the source and the final termination, not only will every piece of gear downstream of the break lose its feed... every device before the break will see an unterminated signal at about double its normal level. (In our old plant, you had to be careful about removing monitors in the production control room: if you pulled a quad VTR's monitor while it was on the air in master control, there was a good chance that viewers at home would see an insanely bright picture until a barrel with a termination was screwed onto the cable. And if someone forgot to switch off a device's internal termination, the feed would be double-terminated and about half level.

Of course, this was back when most of our video gear used screw-on PL259 connectors... and the shield ring would sometimes loosen up and mess with the signal, so that downstream gear would see mostly chroma and very little luminance, and upstream equipment would see pretty much the opposite. This was pretty easy to identify with video signals that showed up on monitors, but nearly impossible to spot when it happened to reference lines. We'd go nuts trying to figure out why devices were intermittently going out of sync.

Nowadays we use better connectors, and equipment is far more robust... but some of the pitfalls do remain.

Jeff

jawsborne
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Re: Adding Genlock

Post by jawsborne »

PID_Stop wrote:
Tue Feb 26, 2019 10:39 am
Just want to add a gentle warning about the tradeoffs of using loopthroughs. My station's original facility used loopthroughs extensively for both reference signals and video signals, and while that certainly reduces the number of distribution amplifiers needed, it can lead to some remarkably non-obvious problems.
Thank you for sharing Jeff! Great points, I can see why it would be hard to pin point a bad reference signal.

Just today, I removed some loop throughs. Our 16 input multiview (BMD) had been setup to loop all sources through to then hit the router. I removed the camera feed loop throughs and DA'ed (that term works right?) them prior to the multiview. Main reason was to reduce latency the mulitview was introducing, but also felt the mulitview was a bigger point of failure than the DAs.
PID_Stop wrote:
Tue Feb 26, 2019 10:39 am
(In our old plant, you had to be careful about removing monitors in the production control room: if you pulled a quad VTR's monitor while it was on the air in master control, there was a good chance that viewers at home would see an insanely bright picture until a barrel with a termination was screwed onto the cable.
Ouch! that's rough.

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Re: Adding Genlock

Post by w9wi »

It comes down to where you're comfortable in terms of the risk/cost balance. I'd never dream of using loopthroughs to feed our network signal to our master control switcher. On the other hand, if I were at a high school building a control room to record baseball games for broadcast on Facebook Live, I'd be quite comfortable with it. We don't know your audience, nor whether you're producing for live broadcast or recording to broadcast later.


Unfortunately, Jeff reminds me of the joys of the good old days:) In modern equipment, the primary video circuits are nearly always internally terminated in 75 ohms. This was not the case in the analog days. You ALWAYS had to use the loopthroughs, if nothing else to attach a 75-ohm terminator.

1. This means we have a drawer chock full of unneeded 75-ohm terminators. (it's heavy!)
2. You were subject to some of the failures Jeff mentions and there wasn't really much you could do about it.
3. Please don't remind me about the day when we discovered we'd been shipped a 93-ohm terminator. (for computer networks)
--
Doug Smith W9WI
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PID_Stop
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Re: Adding Genlock

Post by PID_Stop »

w9wi wrote:
Wed Feb 27, 2019 7:00 am
It comes down to where you're comfortable in terms of the risk/cost balance. I'd never dream of using loopthroughs to feed our network signal to our master control switcher. On the other hand, if I were at a high school building a control room to record baseball games for broadcast on Facebook Live, I'd be quite comfortable with it. We don't know your audience, nor whether you're producing for live broadcast or recording to broadcast later.
Exactly right, and very well stated. I'm not trying to impose a particular idea of how things must be done, only to make sure you realize the tradeoffs.

As far as latency goes, a loopthrough really doesn't add anything measurable to an SDI signal (nanoseconds, perhaps). Even in analog days, we would expect a loopthrough to contribute fairly minimal delay: if you consider that roughly 6" of Belden 8281 cable delayed an NTSC feed by about one degree of color subcarrier phase, the equivalent length of a typical loopthrough would be even less. As a practical matter, the gear you need to watch out for in terms of latency would be anything with a full synchronizer.

Jeff

jawsborne
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Re: Adding Genlock

Post by jawsborne »

PID_Stop wrote:
Wed Feb 27, 2019 9:26 am
As far as latency goes, a loopthrough really doesn't add anything measurable to an SDI signal (nanoseconds, perhaps). Even in analog days, we would expect a loopthrough to contribute fairly minimal delay: if you consider that roughly 6" of Belden 8281 cable delayed an NTSC feed by about one degree of color subcarrier phase, the equivalent length of a typical loopthrough would be even less. As a practical matter, the gear you need to watch out for in terms of latency would be anything with a full synchronizer.

Jeff
Thanks Jeff,

My testing (using a video clip displaying time code with one output running through the mulitviewer's loop through, and another output not, then taking a photo of both displays showing the TC), this showed I was getting about 2 frames of delay.

I'll have to test it again..

jawsborne
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Re: Adding Genlock

Post by jawsborne »

w9wi wrote:
Wed Feb 27, 2019 7:00 am
It comes down to where you're comfortable in terms of the risk/cost balance. I'd never dream of using loopthroughs to feed our network signal to our master control switcher. On the other hand, if I were at a high school building a control room to record baseball games for broadcast on Facebook Live, I'd be quite comfortable with it. We don't know your audience, nor whether you're producing for live broadcast or recording to broadcast later.
Thanks, makes since.

We're pretty much an online shop, who can have a fairly large audience. Some shows live and some recorded. I felt our mulitview was a pretty big point of failure, and added the AJA DAs (HD10DA). Do you guys think those are pretty sturdy? As I prepare to build another control room next year, I would like to get an open gear card-insert setup for DAs. I know Evertz is great, do you have any other recommendations for DAs?

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Re: Adding Genlock

Post by w9wi »

jawsborne wrote:
Thu Feb 28, 2019 1:56 pm
We're pretty much an online shop, who can have a fairly large audience. Some shows live and some recorded. I felt our mulitview was a pretty big point of failure, and added the AJA DAs (HD10DA). Do you guys think those are pretty sturdy? As I prepare to build another control room next year, I would like to get an open gear card-insert setup for DAs. I know Evertz is great, do you have any other recommendations for DAs?
I think what I'm getting at with the risk/cost balance thing is that it's a very personal decision, based on your own assessment of how much trouble happens if something goes down.

I haven't used a whole lot of that Aja "cigarette-pack" gear. On the one hand I'm leery of the wall-wart power supplies -- on the other, we do have four of these de-embedding audio from a character generator, and they've been 100% reliable.

Evertz makes good stuff, although they charge accordingly:) (they do NOT make OpenGear equipment) We use quite a bit of Blackmagic OpenGear DA and de-embedder equipment with success. (and at a better price) We have had a bit of trouble with more sophisticated Blackmagic stuff (format converters) but I wouldn't worry about DAs. The card-frame arrangements do generally have better power supplies.
--
Doug Smith W9WI
Pleasant View, TN EM66

jawsborne
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Re: Adding Genlock

Post by jawsborne »

w9wi wrote:
Thu Feb 28, 2019 9:18 pm
Evertz makes good stuff, although they charge accordingly:) (they do NOT make OpenGear equipment) We use quite a bit of Blackmagic OpenGear DA and de-embedder equipment with success. (and at a better price) We have had a bit of trouble with more sophisticated Blackmagic stuff (format converters) but I wouldn't worry about DAs. The card-frame arrangements do generally have better power supplies.
Ah yes, I was confusing the term open gear with just card-frame. I know Evertz is rock solid and pricey, haven't actually looked at those prices yet though. We used a lot of their card-frame setups at my last shop, all were great except one DA card I would have to frequently reseat for some reason.

Most likely in my future control room I would go with the open-gear / BMD card DAs, glad to hear you like them.

What trouble have you had with the BMD format converters? I am planning on ordering the Teranex AV soon.

jawsborne
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Re: Adding Genlock

Post by jawsborne »

BTW, sorry, just realized I started this thread in the RF Engineering section.

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Shane
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Re: Adding Genlock (OT)

Post by Shane »

I have an AJA shirt I won as a door prize at an SBE meeting years ago. When I wear it around people who aren’t familiar with the brand and they ask me what it means, I just say it’s Spanish for AHA!
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Re: Adding Genlock

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w9wi wrote:
Thu Feb 28, 2019 9:18 pm
Evertz makes good stuff, although they charge accordingly:) (they do NOT make OpenGear equipment) We use quite a bit of Blackmagic OpenGear DA and de-embedder equipment with success. (and at a better price) We have had a bit of trouble with more sophisticated Blackmagic stuff (format converters) but I wouldn't worry about DAs. The card-frame arrangements do generally have better power supplies.
Walk, no RUN, from that Black magic crap. Seriously, it is not good equipment and IMHO, doesn't belong in a broadcast facility. Public access at best. It always runs hot, their support is awful, and it's clunky. AJA is at the low end of the budget scale for Broadcast Gear, and I think they make some fine products. The AJA stuff is much higher quality too. Locking power connectors (unlike BMD using standard 2.1mm style), they don't run hot, proper indicators of service, and their support is outstanding.

If we never buy another BMD device in our building I will be a happy guy. Sorry Doug, just my opinion from my experiences.

Our plant is a mix of AJA, Evertz, and BMD. I like the Evertz stuff. Not crazy about their support in general but overall you don't need it much.
Their manuals aren't easily available online, and I hope they change their course on that, but 10 years later, still hasn't happened. Where I came from before we had the Miranda Densite (Pronounced "Don-Sah-Tay") frames, and they were very nice. The web gui for them was easy to use. They held up in tough environments. The big issue with them was they tended to have power supply issues.
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