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ELI5: HD-SDI and audio sync

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Sean Kurzweil
ELI5: HD-SDI and audio sync
on May 14, 2014 at 12:00:12 am

When dealing with digital audio between two audio interfaces there is the ability in the GUI to set one as master and lock (or slave) the other to the master via word clock, s/pdif or AES/EBU. This insures that the "speed" of the sample rate remains the same between the two devices.

Now, with video devices such as (in my case) 2 Blackmagic Decklink duo cards, there is an analog "Ref In" BNC. I want to use these cards primarily to send audio from one computer to another. My question is this - How do I lock one Decklink to the other for *audio*. My assumption would be to use a third device for genlock and send reference from that to the "ref in" BNC on both Decklink cards.

The unknown factor (to me) is whether or not a video reference signal will also serve to sync audio sampling rates when that audio is embedded in an SDI stream. Typically for audio guys like me we might generate word clock from a video source to sync audio and video thus keeping the two worlds happy but seperate. Here I'm trying to use a video card essentially as an audio card. There is no word clock. And there's no GUI element in the preferences to choose a sync source.

Even the Decklink Extreme 3D (with AES/EBU audio I/O) has no means of choosing a master/slave setup.

okay, my brain hurts - any thoughts?


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