# Description:
# Converts a normalized Butterworth filter to a digital filter.
#
clear
#
# digital cutoff frequency
cutoff_d = 2 
# digital sampling interval
dt = .2 
# continuous cutoff frequency
cutoff_c = (2 / dt) * tan(cutoff_d * dt / 2) 
# normalized filter
num_n = novalue
den_n = novalue
fnbut(6, num_n, den_n) 
# convert to cutoff frequency
num_c = novalue
den_c = novalue
fn2clp(cutoff_c, num_n, den_n, num_c, den_c) 
# convert to digital
num_d = novalue
den_d = novalue
fc2dig(dt, num_c, den_c, num_d, den_d) 
#
# minimum y axis value
ymin = 1e-4 
# maximum y axis value
ymax = 10. 
# title for the plot
gtitle("Digital Butterworth Filter Response")
# plot the digital
fdplot(dt, ymin, ymax, cutoff_d, num_d, den_d)
# scale the horizontal axis
gxaxis("linear", 0., 10.)