Cgs synth

What kind of pot do you need for the "processor". Doesn't this pot
need to be a center detent pot since it should always be at 0 when
it's in the middle position? So when you turn the pot towards the
left, it should be going negative and positive from 0 to the right,
correct? Where can I find a pot like this? I need a knurled type which
is probably rare.

thanks,
pete
--
www.p23.biz