When the switch is open it's in 'deep' mode.
The deep corner (-3dB) frequency is 1/2/pi/R91/C69 = 1/2/3.14/22k/22nF = 330Hz. The gain is highest at low frequencies and decreases at -6dB /octave to level out after 330Hz. R91 sets both the upper corner frequency and the gain above that frequency.
R93 stops the gain from rising below 33Hz.
IMHO R58 is superfluous. It would only do anything if CON2 was disconnected and even then nothing especially useful.