PreSonus TubePRE - Manual (Page 7)

3
80Hz Rumble Filter
A rumble filter is available to eliminate low frequency noise. This
lets you greatly reduce background noise from things such as air
conditioners or wind noise with the flick of a switch without
affecting the desired frequencies.
Mic/Instrument Input
The TubePRE has a separate XLR and 1/4” connector on the back
of the chassis for signal input from microphones (XLR) or
instruments (1/4”).
Drive
The TubePRE provides a Drive potentiometer for controlling the
amount of signal routed to the 12AX7 vacuum tube. This feature
lets you control the amount of tube saturation. Greater levels of
tube saturation give the signal greater warmth and a richer sound.
This works equally well on mics and instruments.