PRESONUS
Figure1
Bypass
If the BYPASS button is not pushed in, the EQ3B is processing the signal (equalizing). Pushed in, the EQ3B is no longer equalizing the signal.
80Hz
The 80Hz button is a low end roll off filter. When pushed in, the 80Hz button causes all frequencies below 80Hz to be attenuated (dropped) by 12dB. This filter can be handy in several live and studio applications. One instance would be for use on a vocal. The 80Hz filter would help reduce the “boominess” of a deep vocal.