What causes a loud tone/noise in Blackmagic ATEM talkback?

Question

Setup

I have a Blackmagic ATEM 4 M/E and one of their studio cameras. I have a headphone on the camera and an active speaker on the ATEM so I can hear talkback.

Problem

There is a super loud whine/tone/whistle/noise. It is similar to a 1kHz square tone. Even if I set volume to minimum it is hearable.

What I tried

I tried to disconnect the cable going into "SDI in" from the camera. The tone is still there but only in the ATEM so the source has to be the mixer. I added a mic to the talkback XLR input but it can't be heard. I also tried to add a sound mixer to this same XLR input and even if I set volume to the max it can be barely heard but the tone is still super loud compared to it. What is the problem?

Answer 1

tl;dr

Make sure none of the SDI outputs of the ATEM are routed back to its inputs.

Talkback feedback loop

The ATEM uses SDI channel 15 and 16 for talkback. If you route one of your SDI outputs to the SDI inputs (either directly via a simple SDI cable or trough a system of devices like record/playback devices) you will get a feedback loop that causes this high tone.

Possible solutions

The simplest solution is to break the loop by removing the cable/devices causing it. Obviously this way you will loose the functionality you tried to add trough it, like having M/E 1 PGM as one of your inputs so you can use it as an input on M/E 2, 3 or 4, so if you would like to keep the loop without the noise you have to deembed or redirect the audio from channel 15 and 16. You can use something like the Decimator MD-HX Cross Converter that can reroute SDI audio channels.