So this isn't a worry/panic or even a concern, just a curiosity about what's happening inside the interface.

I have a Babyface Pro hooked up to an ADI-4 DD via Adat Optical I/O - so that I can use the AES inputs on my monitors.

Recently, when listening to music I decided to try using the EQ on the Main Outs (which are routed to Adat 1&2 Out).

The ADI-4 has a signal presence indicator that lights up above digital 0 (not to to be confused with 0dBFS).

Here's the curious thing. If I play music back through the Babyface with the EQ engaged, the signal presence indicator on the ADI-4 will always show a signal after the music/audio has stopped - even when TotalMix shows absolutely no signal/noise being routed to the main outs.

If I disable the EQ, the signal goes away, the ADI-4 reports no-signal. When I re-enable the EQ the signal stays at digital 0 _until_ audio is passed again, at which point some inaudible noise causes the ADI-4 to show a signal present.

TotalMix shows all signals at UFL.

The behaviour is consistent and repeatable.