The choice between GtrIn (Guitar Input) and EfxIn (Effects Input) determines where the noise gate "listens" to your signal to decide when to open or close. GTRIN I placed in the beginning. Efxin is placed at the end behind the distortion. If you put Efxin behind a reverb, EfxIn may cause the gate to cut off reverb tails prematurely because it hears the noise tails, not just your clean guitar.