Geopsy: Taper

Taper, reached from the Waveform menu, applies a taper (a.k.a. apodization window, a.k.a. window) to the signals in the active signal viewer. The applied taper is a tapered cosine window (Tukey window). By clicking on Taper, a pop-up window appears with the following options:

• "Time Limits" allows to specify the time interval out of which the signal will be set to 0.
• "Width" allows to give the width, in % of the time interval, of the slope of the taper as also defined for the cosine taper filter but in the frequency domain.

Since the Fourier Transform of a boxcar function (too simple tapering window, equivalent to no taper) is a sinc function, the Fourier Transform of a signal without applying an appropriate Taper will be the multiplication of the true Fourier Transform by the sinc function. On the contrary, appropriate tapers have a Fourier Transform closer to a Dirac function that distorts less the Fourier Transform of the signal. It is therefore necessary to apply a taper before going to the frequency domain.

"Taper" modifies the temporary signals in the active viewer.

See also: Window function (Wikipedia)