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Old 5th August 2020, 11:32   #1  |  Link
FranceBB
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Join Date: Nov 2013
Location: Royal Borough of Kensington & Chelsea, UK
Posts: 2,883
Blackmagic DeckLink Audio out of Sync

Hi there,
I've been capturing a lot a tapes ever since I began the Remastering and Digitalization project and I'm using a BlackMagic DeckLink card, however I'm facing an issue now: every now and then there are dropped fields which generate orphan fields and make the audio go out of sync. I'm capturing as lossless 720x576 25i BT601 directly from the SDI output of the VTR, as suggested by Derek but sometimes when there are channel conditions or when the tape isn't playing smoothly, I get those horrible drops that make the audio go out of sync and I have to capture the very same tape again and again 'till it works. Do you have any idea why? It's particularly annoying 'cause I couldn't care less about drops, but at least I expect audio to be in sync... The Sony VTR is auto-referenced, which means that the reference SDI isn't connected to the Blackmagic card, could that be the problem? I thought it was because I was writing directly to one of our 35 TB RAID6 systems and that perhaps there were networking problems, but that wasn't the case 'cause I saved the file locally this time and out of 6 tapes, 1 still had out of sync audio due to dropped fields...

Any idea why?
Sample: https://we.tl/t-0EWmlA8Tgw
You can easily see at TC: 0:00:25.600, frame 640 marks the beginning of the drops. There's the speaker talking and you may not notice it 'cause you can't see his lips, but believe me, audio gets out of sync from there on.


Last but not least, I'm connecting the Reference to the BlackMagic card. I connected it from the BlackMagic Decklink card to the "Ref Video" of the VTR (Blue Cable). Did I do it correctly? And what about the 75 Ohm resistance inside? Is it needed or not? I mean, do I have to keep the switch on or set it to off? I'm sorry but VTR are really not something from my era.


VTR without SDI output only: https://i.imgur.com/oRuLDjT.jpg

VTR with the Reference SDI connected (top left, blue cable): https://i.imgur.com/H3HrlbY.jpg

Blackmagic Decklink card with SDI input (green cable, left) and Reference (blue cable, right): https://i.imgur.com/tOa6TcA.jpg
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