Phoenix Audio DRS-EQ/500 - Mono Class A 4 Band EQ for the API 500 Series - Manual (Page 4)

Here is a description of the units front panel, showing all the switch-able
frequency selector switches and push buttons.
LED LEVEL METER
OUTPUT LEVEL CONTROL
HIGH PASS FILTER ON/OFF
EQUALIZER IN/OUT
BOOST/CUT
HIGH FREQUENCY
SELECTOR SWITCH
HIGH MIDS
FREQUENCY
SELECTOR SWITCH
LOW MIDS
FREQUENCY
SELECTOR SWITCH
LOW FREQUENCY
SELECTOR SWITCH