Various issues in the iir function
Reported by Sergei Steshenko
Originally assigned to Steer Serge
-- Bug description --
Severely wrong bandpass Butterworth filter response ('iir' function).
The to be attached script synthesizes a number of BP Butterworth
filters with
octave-spaced lower and higher cutoff frequencies.
Filter #1, for example, has passband gain of about -260db instead of
the expected
0db.
Only filters #7 and on have more or less decent magnitude response,
however,
filter #7 has about -1.5..+0.5db passband ripple - there should be no
ripple
at all in Butterworth filter.
-- Scilab error message --
-- How to reproduce the bug --
Run the to be attached 'butterworth_filter_problem.txt' script using this
command:
clear;exec('/ibm/home/sergei/butterworth_filter_problem.txt');
ans observe the magnitude plots.