Open the Filter Designer GUI (figure 3)with New Design or Edit Design buttons.
The filter variable name is in the popup-menu in
the upper left corner. The Algorithm popup-menu
contains several options in order to design a filter.
Next to that is an edit box for Sampling frequency.
Depending on the algorithm the main part of the GUI is
different.
For example, with Equiripple FIR as the algorithm,
you may write your specifications (type, passband and
stopband frequencies, ripples and attenuations) in the
left. Then use the Apply button in the lower
left corner and the frequency response is shown in the
axis. The measurements in the right show the needed order
of the filter and actual, measured passpand and stopband
values. The editing can be done with mouse from the
frequency response axis.
A filter can be designed also by setting zeros and poles on z-plane with Pole/Zero Editor as the algorithm. There are buttons for adding, removing and changing the position of zeros and poles.