Total noise CVtot as a function of the feedback strength a when the Hill coefficient is one (M = 1) for different values of noise CVz in the exogenous signal. CVtot is normalized by CVtot–nr, the total noise in the protein when there is no feedback. Other parameters are taken as g0 = 1, Nx = 4, V2x = N2x + Nx, S = 1, and dx = 0.04. The response time Tz is assumed be much larger than Tnr.