ZeroX checkbox in FDSP limiter module - ADAU1787

Hello,

We are experimenting FDSP limiter (not clipper) on ADAU1787. SIgmastudio has limiter module under Dynamic Processors folder. In tuning parameter window of FDSP limiter has ZeroX checkbox, which eliminated some unwanted low-level tone-like noise. Does anyone know how zeroX option works in FDSP limiter?

Thanks!