Fourier Demo Help

      This example demonstrates some of the
filtering capabilities of IDL using fourier series.
The original signals are filtered to remove certain
frequencys while letting the others pass through.
This filtering takes place in the frequency domain and
the fast fourier transform is used to move the
original signal to this frequency domain for filtering
and then back.
      In the example, there are three views that let
you see the filtering process at its various stages.
The button on top of each view lets you pick which
type of view you want.  Pressing the button displays
a menu that lets you choose between views.
      Below the views are the different settings
that specify what type of filter is to be used and the
cutoff frequency for filtering and the width of the
filter when using bandpass or bandreject filtering.
      Different signals are available and can be
selected in the control menu from which this help
text was selected.  Some of the signals are two
dimensional and others are single dimensional.
      As the computation of the filters, FFTs and
multiplications are somewhat intense, the status
indicator will show READY or PLEASE WAIT to indicate
the status of the computation.
      You will notice that when viewing single
dimensional data, the filter cross section, filter
image and shaded surface of filter views are all
plots of the filter.  This is because these views
do not apply to single dimensional filters.