BlackMagic Up Down Cross HD dropping signal

[Toffer]

This is posted on the BlackMagic Forum but there have been no responses thus far.

I have a signal chain comprising, in this order, a couple of iMac's running into a Barco DCS200 switcher feeding a Kramer VM400 HDCP DVI distribution amplifier. An output of which is feeding the BMD Up Down Cross HD via a DVI to HDMI cable.

 

The signal is then fed to an Epiphan Pearl presentation recorder in another room via a BMD fiber converter.

 

The Barco switcher has HDCP switched off and is outputting 1920x1080 at 50hz. The Kramer DA has performed an EDID read and the BMD Up Down Cross HD is set to output 1920x1080p50.

 

On the Epiphan recorder, the signal drops to black and re-appears every 10-15 seconds or so.

 

The specs on the BMD say it can handle computer resolutions up to 1080p60 so should be compatible.

 

I'm assuming the Barco switcher is outputting RGB colorspace and I'm using the BMD cross to convert the colourspace from RGB to video to go over the fiber link.

 

If I replace the BMD Cross with a borrowed Datavideo DAC70 cross converter set to the same 1080p50, the problem is resolved and the image is solid.

 

I'm convinced the problem has nothing to do with HDCP as it has been disabled and other non compliant devices in the system such as monitors display the signal fine.

 

Would anyone have any thoughts as to what the problem may be? It seems to be something to do with the capabilities of the BMD UDX HD.

 

Many thanks.

 

Chris

Edited September 11, 2019 by Toffer

[alistermorton]

If you remove all the mark-up you might get a quicker response...

[Toffer]

Indeed. Apologies. Foiled by a copy and paste from the BMD site. You were too fast. Edited September 11, 2019 by Toffer

[alistermorton]

[david.elsbury]

Something to do with SDI level A vs level B signal?

[david.elsbury]

Sounds like a level A/B issue to me

[david.elsbury]

I appreciate that if you’re not a video guy you might not understand this; but if you do a quick google you’ll find I’m not talking trash: check out the SDI level A and B settings and make sure you are using the right combination with your gear. Black magic had issues in the past that resulted in some incompatibility with other manufacturers kit.

[Anothertom]

This seems like a strange issue, and I'm not saying I can absolutely fix your issue...

 

But the first thing I would try is taking the up-down-cross out of this system and try to replicate the symptoms on a smaller scale. Feed it a 1080p50 over hdmi and spit it out as SDI (at the same frame rate and resolution) and see if it still drops out.

[david.elsbury]

Oh no! What a problem! Perhaps I am able to help with some solid; well intentioned; polite advice! For you see, I am a video guy also, in addition to knowing audio; lighting and computers.

 

Have you considered the possibility of a mismatch between SDI level A and B? You can find some light reading here: https://video.stackexchange.com/questions/18251/whats-the-difference-between-3g-a-sdi-and-3g-b-sdi/18253#18253

 

This might be a possible avenue to solve your issues.

 

Good luck and good day to you!

[Toffer]

1568304011[/url]' post='576789']

This seems like a strange issue, and I'm not saying I can absolutely fix your issue...

 

But the first thing I would try is taking the up-down-cross out of this system and try to replicate the symptoms on a smaller scale. Feed it a 1080p50 over hdmi and spit it out as SDI (at the same frame rate and resolution) and see if it still drops out.

 

That’s a good plan and I will do for sure. My initial hunch was that this was a colour space issue and it may indeed be.

Having had time to further think this through I have a second hunch that the BMD UDX HD may only work with computer based inputs (and by that I mean specifically RGB graphics signals) at 60Hz only.I’ve yet to test both theories tho’.

The problem these days with modern computer graphics cards and digital handshaking / EDID’s etc is there could well be coulurspace switching going on in the background when you directly connect a computer to the UDX HD when the device tells the computer that it wants video colourspace rather than RGB colourspace.

Thereby fooling the user that the UDX is compatible with computer inputs. BUT actually, only if they’re outputting video colour space.

By definition, to me at least, a cross converter should be able to convert between colourspaces.

So to test the theory I need to make sure I’m sending the UDX an RGB signal. I’m no longer in the venue where this setup was used so I need to try and replicate it somehowWith the original setup the Barco DCS200 will have been force feeding the UDX an RGB signal.

Thus far, if anyone is planning on using a BMD UDX HD to connect to a graphics switcher they should double check compatibility first.

[Toffer]

1568222210[/url]' post='576740']

Something to do with SDI level A vs level B signal?

 

Never thought of that David, It has a Level A / Level B dip switch so could it be that simple... ? I’ll set up again and test this out.

Many thanksT