When I have one or more AES sources attached to my ADI-192 with the signal rate converter activated and set to AES as the input, the resulting outputs always have what I can best describe as digital noise:

In the Totalmix FX image above, you can see that the input level for channels 17, 18, 23, and 24, all of which are going through the SRC on the ADI-192 and thereafter via ADAT to an ADI-648 and then on to my MADIface USB, is -138 (not UFL), even though though each AES signal going into the ADI-192 is null/mute (which I've verified by disabling the SRC ).

The same issue is apparent when looking at the bitstreams via DigiCheck NG:

There, you can see UFL displayed for DC voltage but the RMS readings show -144.3 for the affected channels. By contrast, channels 21 and 21, which are not going through the SRC, properly display a zero bit stream.

Interestingly, if I leave the SRC on but disconnect all AES inputs on the ADI-192, the issue also goes away. I suspect it's the SRC disabling itself in the absence of any input signal. In any case, only when all AES inputs are disconnected do the DigiCheck NG Bit States for the affected channels turn into a string of zeroes.

Does this indicate a hardware malfunction or is this a known limitation of the ADI-192?

Thanks for your help,
Adam