dbx AFS224 Quickstart Guide - Manual (Page 6)

11. Perform a sound check on all of the microphones that will be active. Get them as
close to the performance level as possible without feedback. You should get a
reading that is close to “0” dBu on the input meters of the AFS224 when
performing this sound check. When done ask all performers to be very quiet (and
possibly plug their ears) or walk off the stage (and plug their ears).