SDI video distribution vs RGBHV

[kmclights]

I've been asked to comment on a new theatre installation. The theatre consultants proposed an SDI video distribution system for show video (i.e. to be used between Catalyst and projectors in various places). I kind of balked at this and said Catalyst output is DVI and then to RGBHV via Triple Head-2-Go.

Maybe I'm confused, but is there any situation in the next 10-30 years where an SDI distribution system is going to be useful for Catalyst output to projectors/LED walls/etc? I told them a 5-core copper solution terminated on BNCs for RGBHV would be more appropriate. Am I wrong? Should we be looking at fibre? This building is going to be our flagship for the next 30 years, it just feels as if 5 core analog RGBHV is not future proof. But maybe it is?

Someone suggested that CAT5 distribution systems are the way forward, but I've read about transmission rates not being high enough and other problems with systems that use digital switches. There is already two CAT5 ports in every location that the show video port will be, so I don't feel the need to go that route. or maybe i do and need to use a special kind of cat5 cable?

Any help appreciated,

[tharding]

I would suggest using fiber. You can then use different encoders and decoders to get the signal you want.

www.thinklogical.com for example

Many companies have devices for distributing all types of signal over fiber. It would seem to be the most "futureproof" solution. Lots of bandwidth.

The biggest problem I have experienced with permanently installed RGBHV is that is very hard to stop interference from power cabling and other devices.

Cheers

Toby

[NevBull]

There is a DVI over CAT5 solution from TVOne coming out in the next month or so, very affordable

Nev.

[samsc]

'sdi' is only standard definition 720x576PAL 720x486 NTSC.

Can you find out what the cable spec is for HD-SDI?
And how far it goes?

Its going to be much shorter as the bandwidth is 6x greater.

So you will be unlikely to be able to use any sdi cables to go long distances with hd-sdi.

I suspect the short distance hdsdi cables go - mean people then consider having to use fibre and dvi.

The technology life cycles these days are between 18months and 3 years max.

Bettting on any technology outside this timeframe is not going to be a winning strategy.

Richard

[samsc]

There is a DVI over CAT5 solution from TVOne coming out in the next month or so, very affordable

Nev.

cat5 cable is not screened?
Does it use 'special' cat5?

fibre is more resilient to electrical interference.

As you know even unscreened DMX can be a problem in installations.

[samsc]

Many companies have devices for distributing all types of signal over fiber. It would seem to be the most "futureproof" solution.

Toby

...the future is getting closer all the time...

i dont believe much technology at our level lasts longer than 3 years at the moment.

[NevBull]

CAT5 UTP cable is not screened, but CAT5 STP is. But you know that.These adapters are designed to be good for runs up to 250m. But obviously they can be affected by 'atmospherics' as can any signal cable

Nev.

[samsc]

CAT5 UTP cable is not screened, but CAT5 STP is. But you know that.These adapters are designed to be good for runs up to 250m. But obviously they can be affected by 'atmospherics' as can any signal cable

Nev.

there are many levels of things that need to be checked -
there is the signal, the protocol, the connector, the cable.

For example you cannot run cat5 Gigabit 1000BASE-T ethernet to 250m- whatever kindof cable - because of the way ethernet works - not the cable.
its the time delay associated with packets.
that's not a transmission line problem.

[jasonrudolph]

I would also highly suggest getting fiber installed. Especially where it's an installation and you don't have to worry about the fiber getting broken, etc.

With fiber, you can get whatever transmitters/receivers you want. So, you can go SDI, HD-SDI, DVI, Analogue, etc.

RGBHV is very much NOT the way to go I would say. Hum, more prone to failure on a single connector, etc.

The video over cat 5 boxes have the problem that they are just using cat 5 cable, they are NOT doing this over ethernet, so it will not work with ethernet devices (hubs, switches, repeaters, etc) Though I don't know of the new one Nev mentioned, as of yet I have not seen one capable of using ethernet for transmission. The other caveat with these boxes is that while they say they can do up to 1920x1080 (example) resolution, their distance at that resolution is much shorter than what they say is their max distance. The max distance on the product listed is normally at the lowest res the box can run at.

One of the benefits to SDI/HD-SDI is that since it is a broadcast standard, the equipment is going to be around for a while. Unlike computer technology, which is in a constant state of flux, the broadcast world stays much more stable, as the level of investment, etc is much higher. People don't change out $100,000 switchers every couple of years. Computers on the other hand change very frequently. It was HD-15/RGBHV, then DVI, now we have HDMI as well, and now the new "Display Connector" is starting to appear.

That is why fiber gives you the most flexibility. Its probably cheaper to install than the SDI route would have cost. And since it is just the transmission medium, you can make it send and receive whatever it is that you need. You can even change it based on the needs of the show coming in.

[kmclights]

OK, lots of stuff to think about. Thanks. However, nobody has answered the question about the usefulness of SDI/HD-SDI with Catalyst. Is it possible and/ or desirable to output SDI from Catalyst in a theatre environment? Is the quality better/worse than DVI via RGBHV and Triple Head-2-Go?

Also, can HD-SDI be transmitted over the same cable as SDI? From what Richard says above, it sounds like HD-SDI will require a different cable and won't transmit nearly as far.

Sounds like fibre is my best option. Any drawbacks to permanently installed fibre that I should know about? Is the cost of the DVI to fibre codecs significantly more expensive than RGBHV DAs?

Just heard back that they are now proposing a RGBHV network and also pulling some fibre to a few key points, similar to what is happening with the Sound install. I'm just wondering if we need RGBHV at all now. Esp considering the manual patch bay will be RGBHV. Why not just make a fibre patch bay and be done with it? Or, if we can afford it, a digital fibre switching matrix.

Thanks again,

[tharding]

OK, lots of stuff to think about. Thanks. However, nobody has answered the question about the usefulness of SDI/HD-SDI with Catalyst. Is it possible and/ or desirable to output SDI from Catalyst in a theatre environment? Is the quality better/worse than DVI via RGBHV and Triple Head-2-Go?



This can be very subjective. It depends whether you are projecting or using something else. What is the final resolution at the destination? What is it you want to display?

If you are playing back Standard definition clips then SDI will look great but if you want detailed graphics, logos or photos you might be dissapointed with the result compared to the computer screen.

HD SDI on the other hand will give you great resolution but will need a display capable of receiving the signal to reap the benefits.

You also need various boxes (none of them cheap) to convert the signal from the Graphics Card for either SDI or HD SDI

There are so many variables that it is hard to give the definitive answer. You have to look at the whole system and work out what will suffice the highest percentage of the time.

Cheers

Toby

[Mr_P]

All the answers above have missed one key point - what projetors are you using??

There is no one signal that is beter or more appropriate than another - it really depends upon the output device and what control you need over the signal to it

DVI / RGBHV / SDI / HD-SDI all have drawbacks. If you need to subtly change the colour levels between 2 mismatched projectors, you cant do this with anyting apart from RGBHV. DVI/SDI do not have the same amount of control in most projectors.

Distribution of SDI or HD-SDI is simplist - ie singe BNC. SDI can go in excess of 100m decent digial coax, available from most AV resellers. HD-SDI will do 50m on the same cable - Ive not tested further... Also less prone to interference due to nature of signal.

Fiber is not prone to interfeence, but is more expensive and will increase fame delay at every re-conversion. Benefit is that you can transmit most signals over fiber by changing the io box.... but it can be expensive and fiber conectors are not as reliable as they could be. Its the only way to go to transmit DVI over a distance (despite TV-One DVI over Cat5 - there are some drawbacks...)

Cat5 can be a pain and Ive had bad experiences of interference with a number of different cat5/6 transmission systems...

Good old 5wire BC - best way of distributing RGBHV - just be careful with routing to avoid interference. Usually reliable - and you can actually send any of the above signals down the same cable - except DVI (not at the same time though!!!)

So for instalation Id use decent multicore 5 (or more) wire BNC, to give best signal flexibility. If you have the budget, install fiber too as it allows for future compatibility of a range of equipment. If yo do both, then you may as well install a few cat5's too, as the cost will be negligable - this could be used for control too or conversion if desperate

For HD-SDI conversion with low latency, look at the TV-One range (CS2355) less expensive then image-pro HD (and actually available in less than 6 weeks!!!)

To pick up on your questions - when compared to RGBHV at 1024x768, SD-SDI is lower resolution - conversion to HD-SDI is 720 (less) or 1080 more (but upscaling from 1024x768 example) So if connected to TH2G makes little sense, apart from ease of distributing SDI. ***Any signal conversion will cause signal delay*** If live images are to be shown - you need to think about this.

Go look at cost of kit vs your budget. A single fiber converter (one end) will cost you £300 upwards. an RGBHV DA will cost you £60-£150. A fiber matrix will be thousands......

Video is not like lighting or sound - in terms of parching / routing / signals. DMX over ethernet is easy - Soundweb is easy. Video signals are not and cannot be treated in the same way.... avoid patch bays and peripheral processing kit - Keep it simple!

S

[kmclights]

At the moment, I've used stand-alone Catalyst systems with DVI output and an analogue Triple Head-2-Go. The TH2G is located at the Catalyst end and then I've run either 30M VGA leads or use Magenta Research Cat5 boxes. At the moment the resolution for each Panasonic PTD5600 is only 1024X768, but I expect that to rise with time. The Panasonics appear to be able to adjust the RGB of the White Balance using DVI input.

I've spoken to some AV installers and all of them said that RGBHV is OK for exisiting installations, but if you want any kind of future with it, use Cat 5 or fibre. There is already 2 ports of Cat 5 being distributed for use with Lighting equipment and the DMX install is being wired in such a way that it can be converted to ACN or some other ethernet based protocol when an industry standard is clear. In addition, the Sound install is having a certain amount of Cat5 being put in to key locations. I think it is crazy to put even more Cat 5 in for show video. I have said that we should use STP for all Cat 5 installs, instead of UTP due to potential interference issues if we decide to use it for things other than ethernet.

It seems to me that the only thing against fibre is the cost. The codec boxes are more expensive, but it seems that as a technology it is more adaptable and less prone to interference. Plus, as the output for Catalyst is DVI, it seems logical to keep it that way all way to the projector. I take your point about the connectors and about delaying frames at each junction. I assume that a decent matrix would be better than a manual patch bay in regards to this? Not sure we will be able to afford a matrix, but it will help my case to know one way or the other. Does Cat 5 delay frames at each junction as well? Same question with the Cat 5 matrix versus manual patch bay? We are looking at something in the order of 64 outputs through the building and 8 or 16 inputs.

Was thinking of going to ISE next week over in Amsterdam. It looks as if there will be a multitude of people there with knowledgable opinions on this. Plus there are some seminars that discuss this very issue. Anyone else besides Nev going?

[jasonrudolph]

Fiber really isn't all that more expensive than many other options. The cabling, especially for install purposes is relatively cheap (definitely not as cheap as cat 5).

The connectors can be an issue over time, depending on which kind you get.

In all actuality, a Manual patch bay will probably serve you better with regards to delay than a matrix. Essentially, any time you have some form of a "smart" device inline, its going to add some delay, anywhere from one field (half a frame) to 2-3 frames, it all depends on the quality of the device. Most of the time, I find that this added delay is really not an issue at all, as the sounds, etc is all going through similar delays usually and in the end, it normally works out for 99% of the things we do. IF you are doing something like IMAG, or lip-synched stuff, you might have to get with audio to make sure they delay their signal just a bit to match.

Cat 5 is also very useful for control applications though, lots of the projectors today allow you to control things via IP. There are also lots of great devices to do serial over ip, so it works for older stuff too. Serial over IP is also a GREAT thing to have when working with Element Labs stuff and doing mapping, you can even do that over WiFi with the right gear.