Velocity noise performance (defined as the ratio of the noise of an infinite-resolution spectrograph to the noise of the configuration of interest) of a spectrograph without (solid) and with (dashed) the addition of a single filter element. For each resolution, the best FSR in terms of noise performance was selected. At high R, the ideal FSR is roughly twice the pixel size in wavelength, while at lower resolutions, it is ≈0.4 Å, roughly matching the spectral line.