In some cases, the number of available samples is limited and this leads to a DFT spectrum consisting of an undesirably small number of lines.

One way in which the number of lines in the spectrum can be increased is by "zero padding" ie adding zeros to the end of the signal to increase the effective N of the signal. Since the number of lines in the spectrum between 0 and w

The effect is illustrated in the applet below.

eg parameters:-

(0.3, 0.2, 0.1, 0.0, 0.4, 0.5, 0.6, 0.7, 8.0, 1.4) with these 8 samples and no added zeros, the spectrum looks very sparse. Increasing Np to 16 (8 zeros added) doubles the number of lines in the spectrum.

Furthur increase of Np to 128 (120 added zeros) increases the number of lines in the spectrum by 16.

Because the DFT does not use averaging, then the magnitude of the lines do not decrease with added zeros.

COPYRIGHT © 2007 Cuthbert Nyack.