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Filter Realization Wizard
New feature of the DSP Blockset generates floating-point filters automatically
By Anne Mascarin
The Filter Realization Wizard is a new feature of the DSP Blockset that automatically generates floating-point, block diagram models of digital filters from your specifications. The DSP Blockset provides an intuitive, graphical tool for the rapid design, simulation, and prototyping of digital signal processing systems. The addition of the Filter Realization Wizard to the DSP Blockset helps you incorporate the filter design strength of the Signal Processing Toolbox into the block diagram simulation environment. You enter coefficients for the filter through a GUI, making the process of creating custom filter block diagrams quick and painless.
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| Figure 1. The Filter Wizard Graphical User Interface (GUI). |
 Figure 2. A custom Direct Form II, fourth-order, lowpass Butterworth filter created by the Filter Realization Wizard. |
In contrast to the built-in filter blocks of the DSP Blockset, the Filter Realization Wizard creates a filter constructed from individual sum, gain, and delay blocks. Several different filter realizations are available, including Direct Form (I and II), Symmetric FIR, and AR/MA/ARMA Lattice Structures (these realizations are not available as built-in blocks in the DSP Blockset). You can use the Filter Realization Wizard to create a filter architecture, evaluate its performance in your system by running a simulation, and customize the block diagram, if necessary. You can use the Signal Processing Toolbox to generate filter coefficients and then use the Filter Realization Wizard to create the block diagram according to those specifications. The Wizard accepts real or complex data and creates an appropriate filter realization by interconnecting sum, gain, and delay blocks. The resultant block diagram can be placed in a new or existing model. |
To illustrate, we use the Signal Processing Toolbox to design a simple filter and then invoke the Filter Realization Wizard. Type
[b,a] = butter(4,0.25)
at the MATLAB command line to compute filter coefficients for a fourth-order Butterworth filter with a normalized cutoff frequency of 0.25, and store the numerator and denominator coefficients in vectors b and a.
To launch the Wizard GUI (shown in Figure 1), type
dspfwiz
Select the Direct Form II filter from the Architectures pull-down menu. You can then directly enter b as the numerator and a as the denominator. The data type is set to double. To create the block diagram in a new model window, choose New Model.
In this example, we will create a filter block diagram named Butter One. Press the Build button to create the filter realization.
A block named Butter One will now appear in a new, untitled model window. Double-click Butter One to view the filter structure that has been created, (See Figure 2).
The Butter One filter block can now be included in a larger system to perform the specified filtering operation.
