Designing Digital IIR Butterworth-LP Filter using Scilab

Well, after long time busying rushing my assignment, mid term test , mini projects and labs, I am free ~~~ a bit. XP . So today, to reward you all for patience, I present you the sample source code of designing digital IIR filter using the free way Scilab not Scios / Xcos ok !

The 1st time I heard of Scilab, this is what i had on my mind ! A Science Lab ....

(P.S: If anyone of you stumbled this code, you may 'plagiarized' refer it for your projects use, but hey, if your lecturer start ask you some questions of the scilab implementation for this particular Digital Signal Processing projects, don't start come begging/crying to me if it doesn't work as it should be or what is that functions of that coding part  ~~~

And BTW, this code can "run" on Scilab ver 5.2.2  just fine... If you had downloaded my scilab toolboxes... :P)

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//The analog prototype filter specifications
clc ; //Clean the previous console commands
wp = 0.2*%pi;
ws = 0.3*%pi;
Rp = 1;
Rs = 15;
Fs = 0.5;
T = 1/Fs;

//Prewarped Passband and Stopband Frequencies
OmegaP = (2/T)*tan(wp/2);
OmegaS = (2/T)*tan(ws/2);

[n,Omegac] = buttord(OmegaP,OmegaS,Rp,Rs,'s');

disp('The order of the filter is n= ');
disp('n');

//For H(S) transfer functions
[hs,pols,zers,gain]=analpf(n,'butt',0,Omegac);
A=coeff(denom(hs));
B=coeff(numer(hs));
figure(1);
freqz(B,A,512,%pi);
title('n=6 Butterworth Analog LP Filter')

//For H(Z) Transfer Functions
z=poly(0,'z')
hz=horner(hs,((1-(z^-1)/(1+(z^-1))))
C=coeff(denom(hz));
D=coeff(numer(hz));
figure(2);
freqz(D,C,512,%pi);

//Simulating digital filter
t=1:200;
Input=sin(0.1*%pi.*t)+sin(0.5*%pi.*t);

sl=tf2ss(hz);//Transfer functions to syslin representation
y=flts(Input,sl);//Filter the signal

figure(3)
subplot(211)
plot(t,Input);
xtitle('The Signal Before Using Digital Filter','t','y');
subplot(212)
plot(t,y);
xtitle('The Signal After Using Digital Filter','t','y');

===========================================================

You supposed get an output which are like this...


The testing of the digital Filter Signals

That's all , folks and wish you all a happy holiday !

UPDATES:
I had seen my coursemate coding works with a much more superior codes ( Means that they can design their digital butterworth filter without using the special SCILAB toolboxes provided by our lecturer ) Refer to my previous articles ~

Below is the their functions name and how it is used (According to them)

buttordc(): Function to calculate order of lter and its cut-o frequency
buttord(): Function to calculate order of lter
butterc(): Function to design analog Butterworth filter
butterd(): Function to design digital Butterworth lter using Bilinear Z - Transformation. ( BZT )

BTW, Tell you one most important thing~


I love Digital Signal Processing subject ! Wohoo !