Throwing Away Noise to Improve Your Data

It is no surprise that the Fourier transform of noise is noise, so getting rid of noise in you FID will get rid of it from your spectrum as well. If your FID decays long before the acquisition time is over then you have collected unnecessary noise and your spectrum will have a lower than necessary signal-to-noise ratio. You can throw away the noise and replace it with null points before carrying out the Fourier transform. This is shown in the figure below where the improvement in the signal-to-noise ratio is obvious.A better idea is to save spectrometer time, make the acquisition time shorter and avoid collecting the noise in the first place.

Zero Filling

Zero filling is a data processing technique where zero points are appended to the free induction decay before Fourier transformation. The effect of zero filling is to increase the digital resolution in the spectrum. Since the zeros contain no new information, there is no new information added to the spectrum. You can think of it as artificially increasing the acquisition time after the data collection without adding any new information or true resolution to the spectrum.

To zero fill on a Bruker spectrometer, the "si" parameter is increased to a value greater than the number of points collected in the free induction decay. On a Varian spectrometer, the corresponding parameter is "fn".