As indicated in the previous section, the range of precessional frequencies to be observed in an NMR experiment depends on the offset frequency and sweep width. While the offset defines the center of the range, its breadth is governed by the sweep width. So, a sweep width of 2400 Hz (2.4 kHz) covers 12 ppm of chemical shift if the ¹H Larmor frequency is 200 MHz (2400 Hz/200 MHz). Whether these 12 ppm go from 0 to +12, from -2 to +10, or even from +5 to +20 ppm is determined by the offset frequency. Roll your mouse over the images below to see the effect of changing the offset (red curves), the sweep width (blue), and both (yellow).

It is important that the sweep width be set broad enough to encompass all the resonances in the spectrum. If some peaks occur outside of the range, they will be aliased, or folded over, and appear at ncorrect chemical shifts. Furthermore, aliased peaks are usually unphasable.

Generally, standard experiments have appropriate sweep widths setv as default values, so this parameter will not often need to be changed. However, if your sample is inorganic, or an unusual organic compound (such as an organometallic), you should check literature references to insure that the default sweep-width value will cover the expected chemical-shift range.