Vortex Sound Research

Im looking to grab a simple ring modulator but saw that the serge has this 0 - am - RM knob. Now functionally what does this do? Is it just a depth knob for the Modulator? So if I already have a vca patched from my modulator to the modulator in im good to go? Basically just want to make sure that its not another timbre I would lose if I bought a simple ring mod like the doepfer which is the direction I was heading.