filterbuilder function provides a graphical
interface to the
fdesign object-oriented filter
design paradigm and is intended to reduce development time during
the filter design process.
filterbuilder uses a
specification-centered approach to find the best filter for the desired
The design process when using
similar to the process outlined in the section titled Process Flow Diagram and Filter Design Methodology in
the Getting Started guide. The idea is to choose the constraints and
specifications of the filter, and to use those as a starting point
in the design. Postponing the choice of algorithm for the filter allows
the best design method to be determined automatically, based upon
the desired performance criteria. The following are the details of
each of the steps for designing a filter with
When you open the
filterbuilder tool by typing:
Note: This step cannot be skipped because it is not automatically completed for you by the software. You must select a response to initiate the filter design process.
After you choose a response, say bandpass, you start the design of the Specifications Object, and the Bandpass Design dialog box appears. This dialog box contains a Main pane, a Data Types pane and a Code Generation pane. The specifications of your filter are generally set in the Main pane of the dialog box.
The Data Types pane provides settings for precision and data types, and the Code Generation pane contains options for various implementations of the completed filter design.
For the initial design of your filter, you will mostly use the Main pane.
The Bandpass Design dialog box contains all the parameters you need to determine the specifications of a bandpass filter. The parameters listed in the Main pane depend upon the type of filter you are designing. However, no matter what type of filter you have chosen in the Response Selection dialog box, the filter design dialog box contains the Main, Data Types, and Code Generation panes.
To choose the specification for the bandpass filter, you can begin by selecting an Impulse Response, Order Mode, and Filter Type in the Filter Specifications frame of the Main Pane. You can further specify the response of your filter by setting frequency and magnitude specifications in the appropriate frames on the Main Pane.
Note: Frequency, Magnitude, and Algorithm specifications are interdependent and may change based upon your Filter Specifications selections. When choosing specifications for your filter, select your Filter Specifications first and work your way down the dialog box- this approach ensures that the best settings for dependent specifications display as available in the dialog box.
The algorithms available for your filter depend upon the filter
response and design parameters you have selected in the previous steps.
For example, in the case of a bandpass filter, if the impulse response
selected is IIR and the Order Mode field is set
Minimum, the design methods available are
I or II, or
Elliptic, whereas if the Order
Mode field is set to
Specify, the design
method available is
IIR least p-norm.
By expanding the Design options section
of the Algorithm frame, you can further customize
the algorithm specified. The options available will depend upon the
algorithm and settings that have already been selected in the dialog
box. In the case of a bandpass IIR filter using the
design options such as Match Exactly are available.
To analyze the filter response, click on the View Filter Response button. The Filter Visualization Tool opens displaying the magnitude plot of the filter response.
When you have achieved the desired filter response through design iterations and analysis using the Filter Visualization Tool, apply the filter to the input data. Again, this step is never automatically performed for you by the software. To filter your data, you must explicitly execute this step. In the Filter Visualization Tool, click OK and DSP System Toolbox software creates the filter object with the name specified in the Save variable as field and exports it to the MATLAB workspace.
The filter is then ready to be used to filter actual input data.
The basic filter command takes input data
it through the Filter Object, and produces output
>> y = filter (FilterObj, x)
>> help dfilt/filter
If you have Simulink®, you have the option of exporting
this filter to a Simulink block using the
>> help realizemdl