Top panel: median value (top panel) and standard deviation (bottom panel) of the error on the recovered velocities as a function of the velocity difference between the two simulated stellar components. Different lines represent different S/N values per Å: 480 (rms = 0.005), 120, 80, and 24 (rms = 0.1). Bottom panel: two-dimensional maps of the absolute velocity difference between the two stellar components (left panel) and the fit rms (right panel).