Boss FA-1 gain arrangement: parallel resistors, one capacitor

[aion]

Schematic for reference: https://trabantland.files.wordpress.com/2009/05/bossfa11.png

Typical inverting op-amp gain arrangement: R5 combines with the total feedback resistance to set the max gain at ~21x, going down to full zero gain at minimum.

I understand what's going on with R6 and the volume knob - the parallel resistors would provide a different curve than just using the 1MA pot by itself, as well as supplying a much lower resistance (~320k).

However, I am unsure what to make of the C4 capacitor. Since it's 10uF, it should be full-range and shouldn't have any noticeable effect on the EQ. (Right?) So I'm wondering if it's just there to isolate the two resistors in some way, or if I am wrong about it having no EQ effect, or if it serves some other purpose altogether.

[PRR]

C4 C5 keep all DC off the Volume pot.

If the opamps are bipolar, changing Volume resistance would cause DC-scratch in the pot. Maybe not a huge amount. Maybe enough to seem less-good on the showroom floor.