Attenuators are handy in modular circuits. Not all modules have input attenuation so they come in handy. Attenuverters are even handier (is that even a word?). It combines attenuation and inversion of the incoming signal.
Simply put, when the knob is in the center position, no signal passes, it’s fully attenuated. When the knob is fully turned to the right the signal passes unmodified, when turned to the left, the signal gets inverted. And everything in between off course. It’s one of those handy utility modules one cannot do without once you got used to having it in your modular.
The circuitry involved is not extremely complex and lends itself for packaging a few of them in a single module. 4 seems like a good number, unless you’re from china that is, but nevertheless, it nicely uses up a single quad opamp.
As you can see from the above schematics, there is very little going on. A single opamp configured both as an inverting and non-inverting amplifier with unity gain.
In my build I’ve used center dented pots to make life easier (in the center position no signal passes through) but it’s certainly not a necessity. However, do make sure you’re using linear pots.