Our fine TB HPF/LPF Wiki
High Pass and Low Pass Filters | TalkBass.com
has both the peanut butter
and jelly on this caper. That, and the HPF megathread
High Pass Filter (HPF) and Low Pass Filter (LPF) Mega Thread
from which the Wiki was drawn
comprise the total of my theoretical knowledge of HPFs and LPFs.
My empirical finding is, well,
adjust to taste. My HPF is in front of the DI because
No Mud for You. When I play ampless, my DI is the VT Bass. To find my setting for the room — and for the amp, mine or backline — play the lowest note and twist the HPF knob upwards from 30Hz until I hear a change. Then back it off a nudge. Some stages have a sympathetic vibration with a particular note, like the 10th fret D. Adjust the HPF until it's clear.
Always remember to floss after meals