There is no need for R7. Click on the top part of the plot window to V(v1)/I(V1). Next, click the left end to change the selection from Decibel to Linear.
The input impedance is as follows:
1/(1/R1+1/(1/C1+1/(1/R2+1/(R4+1/C4))));
To make it polynomial...
Replace it with a larger GBW OP-Amp (NOT "Slew rate". LM308 and OP07 are about 500kHz, xx741 is about 1M) What happens if C5 is replaced with 5n6 or 6n8?
If you connect a guitar pickup directly to the RAT (unless you enter using an additional buffer or something similar), the difference between 1n and 10n is extremely large. In addition, cable capacitance is added.
5.6n cap "imitates" Gain-Band-Width of the LM308 OP-AMP, but the simulation...
SW_L boosts 106Hz by 3.5db (exact!).
SW_B is 516Hz.
It is not easy to know the corner frequency of SW_H, but it boosts more than 5kHz..
See this calculator.(R9 and R7 can be deleted and analyzed because the impact is minor)