can i discretise a transfer function in "butter" toolbox Matlab?

hi,

if I use the following command, does that make sense for discretisation? or i need to use "c2d" toolbox matlab for that ?

can anyone help me with that.

thanks in advance

the code is for :

A high-pass filter with a cut-off frequency of 0.02 Hz

A model whose filter is a first-order lag system (n=1). And Sampling time: 0.01 s;

n=1;
Wn=0.02; %Hz 
% Transfer Function design
[b,a] = butter(n,Wn,'high');    
figure;
freqz(b,a,(2*59400),0.01)

Answer 1

[Honglei Chen]

Could you explain what you mean by discreization? Using your syntax, the output of butter is already a digital filter so I don't think you need somthing like c2d.

HTH

[ADNAN KIRAL]

ı see, thanks for your reply.

[Honglei Chen]

I assume you mean to recover the original signal from the filtered signal? This is more complicate than it appears. IFFT is not the proper operation for this. To recover the original signal you need to perform the inverse filtering. However, the exact inverse filter may not be available. For example, if your filter removes a certain frequency component, then how can you guess from the filtered signal what was there?

HTH

[ADNAN KIRAL]

thanks for your reply.

I see,

by the way, if i cannot use filtered signal, what is the point of filtering ? i did not get.

cheers.

[Honglei Chen]

I don't understand your question. In general filtered signal is what you want. For example, consider a noise canceling headphone, whatever you are listening to is the filtered signal. I'm wondering if you are confusing the filtering with something else.

HTH

[ADNAN KIRAL]

I want to filter the noise from the signal and then use it as a ground motion in my model. I have filtered the signal now ı need to use filtered signal, but ı could not get filtered signal in time domain. Cheers.

[Honglei Chen]

What you show here is the filter esponse, not a filtered signal. To filter a signal x, you will have to do

y = filter(b,a,x)

The output y is in time domain.

HTH

[ADNAN KIRAL]

thanks.