How to create an advance on-air tally

This tutorial was inspired by a recent training session where an MVS 6520 switcher needed to run a server remotely every time the server appeared on air. Perhaps the best way to do this would be to use serial control via the built-in MVS device ports, as the operator will then have full switcher control of the server, but that wasn’t cabled. GPI control was also not cabled, so the task was to find a way to send the on-air tally before the server was actually on-air. Doesn’t sound possible, but actually it’s fairly simple. This is how to do it:

In menu 7364, Tally Enable, create a new R1 tally on an unused aux bus – I used AUX 10.

Next, in menu 7333, Switcher Output, assign AUX 10 to a phantom output – I used OUT 17. Note that this output doesn’t physically exist, as the 6520 has only 16 physical outputs. But the  address still exists in the switcher’s internal matrix, so it will produce a tally.

Now create a macro with the following steps:

  1. Cut the server on AUX 10
  2. Pause e.g. 8 frames (adjust as necessary)
  3. Cut the server on-air.
  4. Pause 1f or more (to ensure that the server is on Tx)
  5. Cut any other source on AUX 10

Step 5 is necessary to reset the aux bus, or the tally would always remain live.

Now the server gets a tally, and hence a run command, the instant that it’s cut on AUX 10. I like the fact that this trick doesn’t use up any actual switcher resources – you’re just creating a fake switcher output to fool the server :).

Of course the operator still needs to run the macro a few frames before the server will appear on-air, but the annoying freeze frame at the start of the clip is gone.