Data Manipulation Before the Fourier Transform

11 DATA MANIPULATION BEFORE THE FOURIER TRANSFORM 3.11.1 Zero Filling 

Before performing the FT, there are two things we can do to enhance the quality of the spectrum. First, the size of the data set can be artificially increased by adding zeroes to the end of the list of FID data. This process of zero filling has no effect on the peak positions, intensities, or linewidths of the spectrum, but it does increase the digital resolution (fewer hertz per data point) in the spectrum (Fig. 3.31). This can be useful to give better definition 

Other window functions can be used for the opposite effect resolution enhancement (Fig. 3.34). By deemphasizing the beginning of the FID and amplifying the later part, the 

A very simple window function for resolution enhancement is the sine bell (Fig. 3.34), which is just the function sin(x) for x = 0 to 180°. This function grows for the first half of the FID and then brings the signal smoothly to zero during the second half. We saw examples of this window in Chapter 2 (Figs. 2.9 and 2.10). We will see that the sine-bell family of 

Bruker uses the command EM (exponential multiplication) to implement the exponential window function, so a typical processing sequence on the Bruker is EM followed by FT or simply EE (EF = EM + FT). Varian uses the general command wft (weighted Fourier transform) and allows you to set any of a number of weighting functions (lb for exponential multiplication, sb for sine bell, gf for Gaussian function, etc.). Executing wft applies the window function to the FID and then transforms it. 

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