SM Pro Audio MBC502: System 500 Multi Band Optical Compressor - Manual (Page 7)

SM Pro Audio Page 7 of 11 MBC502 Manual
6 Master level
The Master level (labelled 0 to 10) is a rotary control that simply
controls the Master input level to the compressor. Above the Master
level is a Bypass switch. When tuned on, the LED will light and only the
original signal will be heard without any compression.
7 Frequency
The Frequency rotary control is the sweep that selects the frequency at
which the low and high band compressor is crossed over. The MBC502
employs a Linkwitz-Riley 4
th order (24dB/octave) crossover.