Difference between output and input AGN fractional flux contribution at λ₀ as a function of for ten S/N values. Results obtained by fitting synthetic spectra with Starlight with a single (spl) and multiple (mpl) AGN power-law components in the base library are shown in the upper and lower panels, respectively. The shaded area corresponds to the ± 1σ standard deviation around the mean, as computed from ten Starlight fits to each synthetic spectrum.