We use a classic 16.4.2 in a band / live setting. A strange issue is occurring when using the High Pass Filter on the Fat Channel. When engaging the HPF button on a channel, for example, even with the frequency set to OFF, we are noticing a marked drop in levels on the aux monitor mix. I understand that HPF will remove low end, and this could be said to be happening (to a very extreme extent), but I have not noticed any such extreme impact in the front-of-house mix.
When I disengage the HPF then we have a good, clear and loud monitor mix.
Has anyone experienced the same behaviour? Does this indicate a fault or possibly something else? It is definitely not desired behaviour from my perspective - I expect the HPF to affect the signal going to aux and FOH in the same way.
Any hints greatly appreciated.