In this configuration, the fat knob works as an attenuator of the input cap?
(There's probably a good reason why input is usually done by a rotary or switch, instead of something that allows for the whole spectrum between min and max?)
Looks like maybe more changing the value of the input cap by blending 10u into the 10n for what I assume is more bass frequencies--I don't know if that's what you mean by attenuation--it's letting in more rather than diminishing anything, no (?)
[edit: checking my learning rather than correcting is the intent above--don't know if that was evident].