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One particularly insidious effect of aliasing or folding is that not only will NMR resonances fold into the spectral window but noise will as well. This can seriously compromise sensitivity, since noise can extend over an essentially infinite frequency range (so-called white noise) all of which, potentially, can fold into the spectrum and swamp the NMR resonances. It is therefore essential to prevent this by filtering out all signals above a certain frequency threshold with an audio band pass filter after detetction but prior to digitisation.
(Newnes., 2009) High-resolution NMR Techniques in Organic Chemistry.