Signal Processing Toolbox

Converting the Filter Structure

You can use the Convert structure button to convert the current filter to a new structure. All filters can be converted to the following representations:

• Direct form I
• Direct form II
• Direct form I transposed
• Direct form II transposed
• State-space
• Lattice ARMA

In addition, the following conversions are available for particular classes of filters:

• Minimum phase FIR filters can be converted to Lattice MA (min. phase)
• Maximum phase FIR filters can be converted to Lattice MA (max. phase)
• Allpass filters can be converted to Lattice allpass
• IIR filters can be converted to Lattice ARMA

When selected, the Use second-order sections check box instructs the tool to store the converted filter structure as a collection of second-order sections rather than as a monolithic higher-order structure. The subordinate Scale menu lets you select from the following options.

• None (default)
• L-2 (L² norm)
• L-infinity (L norm)

The ordering of the second-order sections is optimized for the selected scaling option. (The tf2sos function that performs the conversion is called with option 'down' for L² norm scaling, and with option 'up' for L norm scaling.)

For example:

• Press the Convert structure button to open the Convert structure dialog box.
• Select Direct form I in the list of filter structures.
• Select the Use second-order sections check box.
• Select L-infinity from the Scale menu for L norm scaling.

Analyzing the Filter

Importing a Filter Design