Re: -18/20 dbfs quandry.
An often overlooked factor is what the meters are showing, do they reflect true peak values, quasi-peak values (PPM), RMS values or more of an average level? With anything but true peak meters the peak levels of the signal could be greater than the levels reflected and while digital console meters typically reflect more of a true peak representation, I have looked though the X32 product data and manual but don't see where the meter characteristics are identified to verify that to be valid for the X32. Perhaps Joe or someone else from Behringer could comment on that.
Another often overlooked factor is where you are metering. Many people look at meters and don't think about how that relates to faders, summing downstream, etc. For example, a meter may read a certain level but if it is post a fader then how does the fader setting factor into the level upstream of that? If you read -18dBFS on a meter but the fader right before the meter is at -20 then what does that say about the level pre-fader?
I also think that what is being said is that with a known signal it is possible to normalize that signal so that the peak level is 0dBFS or just below that, however with live sound you don't know the peak level until after the performance is over, thus to avoid the potential of digital clipping you usually have to leave some headroom.
