MATLAB SIGNAL PROCESSING TOOLBOX 6 Manual do Utilizador descarregar pdf (Página 32)

3 Design a Filter with fdesign and filterbuilder

3-4

To create a filter specification object, evaluate the following code at the MATLAB

prompt:

d = fdesign.bandpass

Now, pass the filter specifications that correspond to the default Specification

— fst1,fp1,fp2,fst2,ast1,ap,ast2. This example adds fs as the final input

argument to specify the sampling frequency of 48 kHz.

>> BandPassSpecObj = ...

fdesign.bandpass('Fst1,Fp1,Fp2,Fst2,Ast1,Ap,Ast2', ...

F_stop1, F_pass1, F_pass2, F_stop2, A_stop1, A_pass, ...

A_stop2, 48000)

Note: The order of the filter is not specified, allowing a degree of freedom for the

algorithm design in order to achieve the specification. The design will be a minimum

order design.

The specification parameters, such as Fstop1, are all given default values when

none are provided. You can change the values of the specification parameters after

the filter specification object has been created. For example, if there are two values

that need to be changed, Fpass2 and Fstop2, use the set command, which takes

the object first, and then the parameter value pairs. Evaluate the following code at

the MATLAB prompt:

>> set(BandPassSpecObj, 'Fpass2', 15800, 'Fstop2', 18400)

BandPassSpecObj is the new filter specification object which contains all the

required design parameters, including the filter type.

You may also change parameter values in filter specification objects by accessing

them as if they were elements in a struct array.

>> BandPassSpecObj.Fpass2=15800;

Step 2

Design the filter by using the design command. You can access the design methods

available for you specification object by calling the designmethods function. For

example, in this case, you can execute the command

>> designmethods(BandPassSpecObj)

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MATLAB SIGNAL PROCESSING TOOLBOX 6 Manual do Utilizador Página 32