Pole-Zero Placement Filter Design

Figure 3 shows the Pole-Zero Placement filter design panel. The panel includes a graphical interface with the z-plane
pole and zero cursors on the left side, and a text-based interface with digital controls on the right side. This panel can
be used to design IIR digital filters by manipulating the filter poles and zeros in the z plane. The poles and zeros
initially may have come from classical IIR designs. You can also use this panel to move or delete existing poles and
zeros directly on the z plane plot for accurate control of their important characteristics. You can describe the poles
and zeros by using either the text entry or the cursors in the z-plane plot. As the cursors are changed, the text entries
update automatically. Likewise, as the text entries are modified, the pole/zero cursors update automatically. The pole
and zero locations in the z-plane, the characteristics of each pole and zero, the gain, and the sampling rate fully
describe pole-zero filter designs. Any change in these parameters corresponds to a change in the filter coefficients.
The DFD Toolkit matches the poles and zeros and creates stable second-order stages for IIR filter coefficients. It then
uses these coefficients to compute the filter magnitude response. The Magnitude vs Frequency plot updates
automatically whenever the poles or zeros are changed giving an immediate graphical feedback to the users pole-zero
filter designs.