Signal Processing Toolbox

Designing a Filter with the Pole/Zero Editor

To design a filter transfer function using the Filter Designer Pole/Zero Editor:

1. Select the Pole/Zero Editor option from the Algorithm list to open the Pole/Zero Editor in the Filter Designer display.

   

2. Enter the desired filter gain in the Gain edit box.
3. Select a pole or zero (or conjugate pair) by selecting one of the (pole) or (zero) symbols on the plot.
4. Choose the coordinates to work in by specifying Polar or Rectangular from the Coordinates list.
5. Specify the new location(s) of the selected pole, zero, or conjugate pair by typing values into the Mag and Angle fields (for angular coordinates) or X and Y (for rectangular coordinates) fields. Alternatively, position the poles and zeros by dragging the and symbols.
6. Use the Conjugate pair check box to create a conjugate pair from a lone pole or zero, or to break a conjugate pair into two individual poles or zeros.

Design a new filter or edit an existing filter in the same way.

Note    Keep the Filter Visualization Tool (FVTool) open while designing a filter with the Pole/Zero Editor. Any changes that you make to the filter transfer function in the Pole/Zero Editor are then simultaneously reflected in the response plots of FVTool.

Positioning Poles and Zeros

You can use your mouse to move poles and zeros around the pole/zero plot and modify your filter design.

Icon	Description
	Enable moving poles or zeros by dragging on the plot
	Add pole
	Add zero
	Erase poles or zeros

You can move both members of a conjugate pair simultaneously by manipulating just one of the poles or zeros.

To ungroup conjugates, select the desired pair and clear Conjugate pair in the Specifications region on the Filter Designer.

When you place two or more poles (or two or more zeros) directly on top of each other, a number is displayed next to the symbols (on the left for poles, and on the right for zeros) indicating the number of poles or zeros at that location (e.g., for three zeros). This number makes it easy to keep track of all the poles and zeros in the plot area, even when several are superimposed on each other and are not visually differentiable. Note, however, that this number does not indicate the multiplicity of the poles or zeros to which it is attached.

To detect whether or not a set of poles or zeros are truly multiples, use the zoom tools to magnify the region around the poles or zeros in question. Because numerical limitations usually prevent any set of poles or zeros from sharing exactly the same value, at a high enough zoom level even truly multiple poles or zeros appear distinct from each other.

A common way to assess whether a particular group of poles or zeros contains multiples is by comparing the mutual proximity of the group members against a selected threshold value. As an example, the residuez function defines a pole or zero as being a multiple of another pole or zero if the absolute distance separating them is less than 0.1% of the larger pole or zero's magnitude.

Editing Signals, Filters, or Spectra in SPTool

Redesigning a Filter Using the Magnitude Plot

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