MATLAB: The error information when i use fdesign.lowpass to design a filter.

fdesign

the code:

 h = fdesign.lowpass('N,F3db,Ap,Ast'  ,14, 0.93,0.1,60);

the error message is :

There is no enumerated value named 'N,F3db,Ap,Ast'.

But the 'N,F3db,Ap,Ast' is listed in the help info of the fdesign.lowpass.

do you know why this happened?thank you very much.

Best Answer

Notice:

      Note:   Specifications strings marked with an asterisk require the DSP System Toolbox&trade; software.

That entry is one of the ones marked with an asterisk.

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MATLAB: Fir and iir filtering

You have to know your filter specifications. If you do, you can do both with fdesign.lowpass and fdesign.highpass

fdesign.lowpass and fdesign.highpass have different specification strings which support different filter designs.

The default string 'Fp,Fst,Ap,Ast' supports both FIR and IIR designs.

Here is an example:

Design a lowpass filter with a passband frequency of 1 kHz, a stopband frequency of 1.5 kHz, passband ripple of 0.5 dB, and stopband attenuation of 40 dB. The sampling frequency is 20 kHz

   d = fdesign.lowpass('Fp,Fst,Ap,Ast',1e3,1.5e3,0.5,40,20e3);
   designmethods(d)  %shows which designs are valid for this spec
   Hdeq = design(d,'equiripple'); % FIR filter
   Hbutt = design(d,'butter'); %IIR design

MATLAB: Are there differences in the filter coefficients generated via FDATool and from using the MATLAB command ‘fdesign.lowpass’

FDESIGN uses the FIRGR function while FDATool uses the FIRPM function.

FIRGR and FIRPM both design equiripple filters but they use different implementations of the Parks-McClellan algorithm. Thus, they may return different answers.

In order to design filters graphically and ensure that the results are consistent with FDESIGN, use the FilterBuilder GUI instead of FDATool.

Best Answer

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MATLAB: Fir and iir filtering

MATLAB: Are there differences in the filter coefficients generated via FDATool and from using the MATLAB command ‘fdesign.lowpass’

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