FabFilter User Forum
Louder Volume When EQ Cut
What you're seeing is completely normal and a result of the fact that any filtering process (of course) alters the waveform.
Filtering (both digital and analog) introduces phase changes, which means that different frequencies in the signal are slightly delayed in different ways. So this may also lead to different peak values...
Of course, the audible volume doesn't change at all!
Hope this helps,
Floris (FabFilter) — Jan 23, 2015
This is an example of what happens to me all the time. If I try to take out some low end on a particular track, the volume goes up. When I expect to have more headroom, I get less. If I bring it back to equal volume, it sounds like shit when A/B. Why do I get more volume instead of less?
www.youtube.com/watch?v=DPhdDk1aSJU