Apodization can increase from light (like Happ-Genzel) to heavy (like Blackman-Harris). The heavier the function, the more affect you will see on lineshape. For most normal uses, when the resolution is 4 wavenumbers or more, even heavy apodization does not distort spectra badly. However, as the lines narrow, as in gas-phase spectroscopy, the affect of apodization can be profound. Strong apodization in broad peaks improves the signal to noise over Boxcar (essentially no apodization) by a lot with minimal effect on linewidth. H-G was the original OMNIC default (and still often is) due to its “gentle” effect on linewidth coupled with decent signal to noise. Generally, S/N improves in the order H-G, Norton-Beer Weak, NB-Medium, NB-Strong, Blackman-Harris, while lineshapes are also affected more in the same order.