DuBoi seems to be saying one channel’s trim-gain knobs and tone controls seems to be affecting the other channel’s metering. That sounds like either a hardware defect or a firmware bug. I’ll have to see if that happens at all on mine.
In your case, Mufasa, if iso is on and the tone knobs for that channel are tweaked at all, then the iso is in the process path and you get a fixed amount of phase distortion or ‘group delay’ that can produce a difference in level beyond the EQ. X1800 bypasses the iso for a channel when its tone knobs are all centered, though. On the DB4 they seem to have went all in for coloration and might not have even tried to get the delays aligned at the corner frequencies… like with Butterworth or Bessel instead so they get less overall distortion, but more pleasing coloration and does even weirder things… especially at the joins. I think everything’s more aligned at the corner frequencies on the X1800 but less lush than DB4 in iso.
Anyway, the DB4 does a significant boost that shows in metering when in iso mode… way more than you’re going to see from the X1800 isos that I’ve noticed. I suspect you’re just seeing probably the sensitivity around the 12 o’clock on the X1800. Mine seem pretty close on both X1800s, but I think I’ve noticed a little touch of difference in the pot alignment. Nothing big. Don’t forget to use your eyes and ears and don’t just stick the trim-gains at some spot and never touch them.
I’m very fond of the trim-gain range and sensitivity on the Denon mixers, old and new. I find the Xone, Mackie, and Rane trim-gains way more problematic. Probably the only thing some of you might like on them is the unity detents on the trim-gains of the Xones and Mackies, but I think those detents largely useless. The MP2015 trim-gains are currently way out of whack in their latest firmware.