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Old July 16th, 2008, 11:25 AM   #1
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Simple question on Flash XDR

Hello,

I am hoping Convergent can answer a simple question for me. I need to know if the Flash XDR unit can "pass-through" video on it's SDI ports. What I am after is a way to plug video from a source, into the SDI port, and get video out of the SDI port on the other end, live.

If it can do this, is the video being affected in route. Meaning is there a codec inbetween so that I am inputting one thing and perhaps getting something out.

And would the passthrough change if I was actively recording or not.

I am trying to develop a workflow and I need to know if the XDR needs to be the last link in the chain, if it can be in the middle of the chain, or if we are going to have to "Y" a signal off to it, to keep it out of the chain.

Thanks
Perrone Ford is offline   Reply With Quote
Old July 16th, 2008, 11:37 AM   #2
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The Flash XDR has an SDI Out which is re-clocked (presumably) from the (master) time-code input. This would be of no consequence if you want to also hook up a directors monitor via SDI, but you need to plan for this in other situations.

On the CD website there are some usage scenarios as well.

George/
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Old July 16th, 2008, 11:55 AM   #3
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Basically what I am after is this type of flow.


Source Cam (SDI OUT) > XDR > CC Encoder > VTR > Broadcast

This inline processing would allow me to originate video with HD-SDI, record that to the XDR (or pass it through), flow to our Closed Captioning Encoder, flow to a VTR that records the captioned signal, and then flow out to broadcast.

If the XDR cannot pass through the video then we will have to split the signal right out of the camera to feed the XDR separately from the rest of the workflow.


-P
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Old July 16th, 2008, 12:51 PM   #4
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Given the HD SDI out, this should work just fine. I'm not sure how the reclocked timecode will turn out, but that shouldn't affect your proposed setup.

George/
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Old July 16th, 2008, 07:01 PM   #5
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Quote:
Originally Posted by Perrone Ford View Post
Basically what I am after is this type of flow.


Source Cam (SDI OUT) > XDR > CC Encoder > VTR > Broadcast

This inline processing would allow me to originate video with HD-SDI, record that to the XDR (or pass it through), flow to our Closed Captioning Encoder, flow to a VTR that records the captioned signal, and then flow out to broadcast.

If the XDR cannot pass through the video then we will have to split the signal right out of the camera to feed the XDR separately from the rest of the workflow.


-P
Hi Perrone-
Your dataflow will work fine, the XDR does give you a reclocked HD-SDI output. The HD-SDI delay is very short, on the order of one horizontal line. So, the time-code should also match.
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Old July 16th, 2008, 07:17 PM   #6
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Dear Perrone and George,

Your workflow will work fine. The incoming HD-SDI will be presented on the output HD-SDI port (unless you set the Flash XDR otherwise, there are other options).

If you have, for example, an original XL H1 which does not have timecode or audio embedded in the HD-SDI, the Flash XDR output will have the timecode and audio embedded automatically, using the external timecode and external audio inputs.

George,

Yes, the HD-SDI is reclocked, but this does not affect the timecode.

The Flash XDR works as a "Reclocking Repeater" as opposed to an "amplifier".

The HD-SDI signal, at 1.485 Gigabits per second requires good BNC coax and there is a length limitation. Each extra connection subtracts from the maximum usable length.

Now, please be advised that with proper cable, the usable length is quite long.

If the Flash XDR just put out the incoming HD-SDI signal on the outputs (without reclocking), then the length limitation would be a problem in some cases.

A "Reclocking Repeater" completely regenerates the signal. In essence, you get another "maximum length" to work with.

An "Amplifier" amplifies the signal and the noise.

A "Reclocking Repeater", receives the analog signal, amplifies it, if necessary, and then outputs a new (clean) signal without any noise.

If you are not embedding the external timecode, then the incoming timecode will be presented on the HD-SDI output without modification.

In essence, a "Reclocking Repeater" is an "Ideal Amplifier", it amplifies the signal, but not the noise in the signal.

This is the magic that is possible by sending a digital signal, as analog, over a cable.
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Old July 16th, 2008, 08:35 PM   #7
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Thanks for the info guys.

It does not bring up an interesting question. What is my maximum cable length assuming we get broadcast quality cable? I ask this, because it may well affect how we position things in the flow. It might be advantageous to move the XDR halfway between the camera and the CC Encoder depending on the length of that run. Can we do this with optical cabling?

[EDIT]
I think I answered my own question. Excellent article here:
http://www.extron.com/company/article.aspx?id=lvdg_ts

-P
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Old July 17th, 2008, 03:30 AM   #8
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Dear Perrrone,

Thank you for posting that article.

The "Maximum HD-SDI Cable Length" question is a tough one.

Wikipedia, in their HD-SDI article says: "...typically 100 meters".

But, a lot depends on:

1. The quality and type of cable, and
2. Whether it is a "one cable" or multiple cables connected together, and
3. The quality of the connectors, and
4. The quality and design of the receiving electronics (and the transmitting electronics).

There is a lot of HD-SDI in use, so I think the best answers should come from those who are using it in real-world applications.

Yes, you can transmit HD-SDI over fiber optic links, which can work over much longer distances. And, one can always use a "reclocking repeater", if necessary.

For short HD-SDI cable runs, you can use less than "up to spec" BNC cables. It is an analog signal transmitting digital data. It is easy to tell if it works or not. (It generally just does not work at all, if the cable is not adequate.)

For longer lengths, getting the proper, high quality, "up to spec" cable is important, or use a fiber-optic link, or a wireless link. There are options available.

One of the advantages of the Flash XDR and the nanoFlash is that the signal is being recorded close to the source (the camera). As such, the recording should be good, even if there are troubles due to downstream cables or equipment.
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