Hi Deniz,
Inorder to call "filter" function, you need to pass the denominator and numerator coefficents for the rational transfer function. To obtain the transfer function from the filter difference equation, you can apply Z-transform. For the FIR filter, the coefficients can be computed as:
Z-Transfrom gives,
rearranging,
From the transfer function, numerator and denominator coefficients are assigned to variables "b" and "a" respectively, and passed to "filter" function along with input signal.
n=-5:0.1:5;
x= cos(0.1*pi*n)+cos(0.5*pi*n)+cos(0.9*pi*n);
b=[0.4 0.3 0.2 0.1];
a=1;
y=filter(b,a,x);
plot(n,x);
hold on;
plot(n,y);
legend('signal','filteroutput');
hold off;
Similarly, you can filter "x" using IIR filter.
Hope this helps!
