I came across this circuit as part of a larger circuit in a guitar effect pedal:
I was wondering about the function of the resistor \$R_1\$. My calculations show that the same transfer function can be achieved with or without \$R_1\$ (leaving out \$R_1\$ just means that we need to change the other resistor values). The only difference that I can see is the change in input impedance of the circuit. Is this the only function of \$R_1\$ (i.e., reduce/define the input impedance), or is there anything else I'm missing?