error with using filter

Hi all,

I have to filter few signals and I wrote the following code:

Fpass = 40;   % Passband Frequency
Fstop = 45;   % Stopband Frequency
Apass = 1;    % Passband Ripple (dB)
Astop = 80;   % Stopband Attenuation (dB)
Fs    = 100;  % Sampling Frequency

h = fdesign.lowpass('Fp,Fst,Ap,Ast', Fpass, Fstop, Apass, Astop, Fs);

Hd = design(h, 'butter','MatchExactly', 'stopband','SystemObject', true);

a=rand(1000,1);
a=filter(Hd,a);

I get the following error:

Undefined function 'filter' for input arguments of type 'dsp.BiquadFilter'.

Why do I get that error?

Thanks

Regards

Pietro

Answer 1

[Honglei Chen]

dsp.BiquadFilter is a System object, so its main method is step(). Try

a = step(Hd,a)

[Gustavo Machado]

Honglei, I've encountered the same problem Pietro had and used step() to apply the filter, but the filter was inefficient, seems like it didn't filter the data.

I've posted a question regards my problem. I used the sosfilt(Hd.SOSMatrix) to filter my data but came across the problem described in this topic: https://www.mathworks.com/matlabcentral/answers/466353-difference-between-fvtool-filterobject-and-fvtool-filterobject-sosmatrix

I'd highly appreaciate if you could take a look at it.

Thanks in advance,

Gustavo