Re: Help-octave Digest, Vol 43, Issue 52

[bharat pathak]

Dear Nuncio,

 

    This is the code I had written for design of butterworth

    filter. It also has an example to compute the order.

 

    You need to send me "Virtual Coffee" if you like the

    code.

 

Regards

Bharat Pathak

 

Arithos Designs

www.Arithos.com

 

DSP Products and Trainings.

 

//-------------------------------------------- code to design butterworth filter with given specs.

 

clear;
close all;
hold on;

 

%------------------------------------------ specification section -------------------------------------------

 

ap    = 3;   % ripple in db
as    = 50;   % stopband attenuation in db
fp    = 2000;
fs   = 2500;
Fs   = 8000;

 

%-------------- let the design begin ----------------------------------------------------------------------

 

Fn   = Fs/2;
Wp   = fp/Fn;
Ws   = fs/Fn;

 

%------------------ compute the order and get the numerator and denominator polynomial

 

[N, Wc]  = buttord(Wp, Ws, ap, as);
[b, a ]    = butter(N, Wc);

 

%-------------- plot the magnitude response in log domain with frequency as x-axis

 

[hz, f]  = freqz(b, a, 1024, Fs);
plot(f, 20*log10(abs(hz)));

 

%------------------------------------------------------------------ !! Coffee Time !! -------------------------------

From: Nuncio M

Sent: Monday, October 26, 2009 10:24 AM

To: address@hidden

Subject: Re: Help-octave Digest, Vol 43, Issue 52

Hi all,
          I am trying to use the butterworth filter.  After filtering the signal I feel there is a slight phase shift.  HOw can this be removed?.  Also how to specify the order of the filter.
eg; butter(1,fc/nysq) , does this mean a first order butterworth filter?.
Thanks and regards




--
Nuncio.M
Research Scientist
National Center for Antarctic and Ocean research
Head land Sada
Vasco da Gamma
Goa-403804

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