Octave Filter Design Example

pkg list
pkg update

pkg load signal
 
% Simple but has a large transition band and only about 50 to 60 db attenuation
freqz(fir1(63,0.125))

% --- Parks-McClellan lowpass Filter
n = 64
f = [0.0 0.3 0.4 1.0 ];
a = [1.0 1.0 0.0 0.0];
w = [1.0 0.1];
b = remez(n, f, a, w);
 
[h,w] = freqz(b,1,512);
plot(f,a,w/pi,abs(h))
legend('Ideal','remez Design')
xlabel 'Radian Frequency (\omega/\pi)', ylabel 'Magnitude'

% example of 100dB filter
f = [0.0 0.1 0.2 1.0 ];
a = [1.0 1.0 0.0 0.0];
freqz(remez(128,f,a));