[Octave-bug-tracker] [bug #53855] [octave forge] (signal) butter band pass filter with higher order has strange pass band

[Renato]

Follow-up Comment #2, bug #53855 (project octave):

Same problem in MatLab...
File attached.

IF you increase the high frequency cut-off, the result is much better. But I
didn't undestand why...

In the example below, I changed the high-frequency cut-off from 100Hz to
200Hz.

++
n = 5;
hpf = 200;
lpf = 10*hpf;
[b, a] = butter (n, [hpf/22050, lpf/22050]);
freqz (b, a, 4096, 44100)
ax = findall (gcf, 'type', 'axes');
set (ax, 'xlim', [hpf/4 lpf*4]);
set (ax, 'xscale', 'log');
subplot (2, 1, 1);
set (gca, 'ylim', [-35 3]);
--

(file #44120)
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Additional Item Attachment:

File name: test_RYamane.png               Size:54 KB


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