"The series HG and HQ have one RCA Audio in. The series HU has up to 8 RCA audio channels in.
By default, the RCA Audio in is always active. When the coax camera has the option audio over coax and the option is not active, see picture below."
How to activate the audio over coax?
Open the setting option via start on the XVR menu.
Then select Edit Camera.
A. Click on Camera Signal
B. Click the option Audio Over Coax arrow down
C. And select ON (repeat on the rest of the channels)
D. Click on Apply to save