Bad Inframe Edits.

[Shane Chadder]

It might be a cable length problem. Are you genlocking the deck from the output of the Decklink card? If so be sure the cable length for the reference and the signal are the same.

The quickest fix for a sync problem is a delay box. Introduce delay on the deck ref. in until the shift is corrected. If the shift gets worse move the delay to the video in. If it is a small shift you can use video cable for the delay, 10ft is 15.5 nanoseconds.

If you think this is fun try timing an analog studio. I think this is why video engineers lose their hair.

[Bob Zelin]

Hi Kai –
It’s not a cable legnth issue. Small amounts of cable are only going to affect the subcarrier phase delay, not enough for H timing. I can’t believe that you are having a problem like this. I ASSUME that you have a SINGLE NTSC black generator feeding the Genlock input of your Beta VTR Ref Video input, and the Genlock input of the Blackmagic card. Am I correct about this Kai ? No tricks now.

You have not stated what Beta VTR you are using, but older Beta VTR’s may have a 2 field/4 field switch on them. I have not discussed color framing issues in years, but you should black your tape (you are doing an INSERT EDIT into your master – aren’t you ? ) – with composite black from your black generator in 4 field position. Leaving it in 2 field allows the edit controller (from the linear editing stone age) to control the color framing, and can potentially create a shift. So Black your tape in 4 Field, and leave it in 4 field, and the VTR will color frame the edit properly without a shift.

If you were to try the “cable delay trick” – which won’t work, by the way – the way to generate advanced sync to make this happen is to get a second professional sync generator that can genlock to your house black generator, and send this “pro” sync generator (not a Horita – but a box like a Sigma, Leitch, Videotek or Tektronix that has H phase adjust) into the VTR. You could then turn the H Phase to advance sync the VTR – but THIS IS NOT YOUR PROBLEM. This was a “trick” we used to do with everything from Ultimattes, to Chyrons, to the old Video Toaster that had to be advanced synced into analog video switchers.

Bob Zelin

[Aaron Neitz]

You said ‘only in analog.’ meaning have you tried a carpture of this SP tape from a Digibeta over SDI? Try to confirm if that shift is happening as it hits tape, or it is a problem in the Decklink A-D

[Shane Chadder]

If you find you need a delay box they can be had new for under $100 https://www.markertek.com/SearchProduct.asp?item=VP0010&off=9&sort=prod

Its best to put the delay on the reference of either the deck or the decklink (whichever shifts the right direction) rather than the signal.

Good luck
Shane

PS Bob
I’m guessing 50ft of cable will shift 1 pixel? 63ms per line / 720 pixels per line.

[Kai Whittaker]

Hi.

Sorry to take so long but I posted this question a few times with no replies. It’s nice to see some suggestiopns, thank you all.

To answer Bob’s questions:

1 – Yes, we have One single TBC feeding the deck. then I loop the black through the deck and out to the genlock input of the decklink card. I don’t output black to deck during capture (just to let you know).

2 – The VTR I’m using is a SONY PVW-2800. I’ve also tried using a Sony UVW-1800 with similar results.

I guess the test now is to try blacking a tape using the 4 field option, then to output from the AVID, then digitize in FCP with the decklink, then lay back to the same tape. IF there’s srtill a shift then I’ll know it’s something else…

I discussed this issue a long time ago with some of the BMD staff and in the end it was what they called analogue blanking… A term I’m not familiar with, but perhaps it’s another word for teh same thing.

Thanks again for your help.

Kai

[Kai Whittaker]

Hunh?

I’m capturing using the y, r-y, and b-y wires on my decklink SP. There’s no SDI involved. Decklink SP doesn’t have SDI input.

Thanks anyways!

Kai

[Kai Whittaker]

interesting…

my cables are about 3 feet long so i think the delay in my case is neglilgible.

Thanks!