Left: noise budget contributors: total (blue), shot (orange), stray light (green), readout (red), dark current (purple), and pixel gain variability (brown). Right: portion of the simulated, not convolved, spectrum after the addition of the noise. The focus is on spectral order 84, which contains the Si III triplet around λ4553, λ4567, and λ4574 lines and is used for asteroseismic diagnosis.