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Converting the Filter Structure

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Converting to a New Structure Converting to Second-Order Sections

Converting to a New Structure

You can use Edit > Convert Structure 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

• Lattice ARMA

Note   If you have Filter Design Toolbox product installed, you will see additional structures in the Convert structure dialog box.

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

• Minimum phase FIR filters can be converted to Lattice minimum phase

• Maximum phase FIR filters can be converted to Lattice maximum phase

• Allpass filters can be converted to Lattice allpass

• IIR filters can be converted to Lattice ARMA

Note   Converting from one filter structure to another may produce a result with different characteristics than the original. This is due to the computer's finite-precision arithmetic and the variations in the conversion's roundoff computations.

For example:

• Select Edit > Convert Structure to open the Convert structure dialog box.

• Select Direct-form I in the list of filter structures.

  

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Converting to Second-Order Sections

You can use Edit > Convert to Second-Order Sections to store the converted filter structure as a collection of second-order sections rather than as a monolithic higher-order structure.

Note   The following options are also used for Edit > Reorder and Scale Scale Second-Order Sections, which you use to modify an SOS filter structure.

The following Scale options are available when converting a direct-form II structure only:

• None (default)

• L-2 (L² norm)

• L-infinity (L^∞ norm)

The Direction (Up or Down) determines the ordering of the second-order sections. The optimal ordering changes depending on the Scale option selected.

For example:

• Select Edit > Convert to Second-Order Sections to open the Convert to SOS dialog box.

• Select L-infinity from the Scale menu for L^∞ norm scaling.

• Leave Up as the Direction option.

  Note   To convert from second-order sections back to a single section, use Edit > Convert to Single Section.

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Editing the Filter Using the Pole/Zero Editor

Importing a Filter Design

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