MATLAB: What is the difference between “fdesign” and “fir”

fir

Could u please explain me about the difference between "fdesign" and "fir" for design digital filter?

Best Answer

d = fdesign.response(spec)

defines a particular filter specification. Based on that specification, if you do

myFilter = design(d)

you will get a filter which you can used to filter a signal by invoking

y = filter(myFilter,x)

This approach allows you to choose among eligible design methods at the design stage.

On the other hand,

b = fir1(n,Wn,'ftype',window)

is specifically for designing an FIR filter using window method, so you have to know that you want to use that particular method before you design that filter. What you get is simply the filter coefficients for the resulting FIR filter and you can use that to filter the signal via

y = filter(b,1,x)

If you happen to choose to design an FIR filter using window method in the fdesign approach, then you should get equivalent filters.

HTH

Related Solutions

MATLAB: Blackman FIR bandpass filter design

Hi olga,

There is a subtle difference between the specification of an IIR filter and an FIR filter. Because you are designing an FIR filter, you need to use 'N,Fc1,Fc2' instead of 'N,F3dB1,F3dB2'. Here is an example

h = fdesign.bandpass
h.Specification = 'N,Fc1,Fc2'
Hd = window(h,'window',@blackman)
fvtool(Hd)

HTH,

Honglei

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

Best Answer

Related Solutions

MATLAB: Blackman FIR bandpass filter design

MATLAB: Fir and iir filtering

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