RPM Cutoff Bass Shakers

Morning all

Very quick question, trying to setup the idle vibration for the Audi RS3 in iRacing.  Basically I want a low vibration (i've tested at 15Hz which i quite like so that fine) but only when its idling - 800rpm.  above that I want it to disappear.  I've ready a couple of posts in various forums that make it appear that this can be done, however they don't actually show you.  I've a feeling it might be something to do with the response curve but I don't know.  If it is, what do the X & Y axis correspond to?

TIA