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

[Mike Miller]

Update of bug #53855 (project octave):

              Item Group:        Incorrect Result => Inaccurate Result      
                  Status:                    None => Confirmed              
                 Release:                   4.4.0 => dev                    
                 Summary: [signal] butter filter with strange results =>
[octave forge] (signal) butter band pass filter with higher order has strange
pass band

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Follow-up Comment #1:

Confirmed here. It would be useful to compare the filter coefficients to other
software (e.g. SciPy).

Here is a simpler example, since I'm not sure where the 'noise' and
'normalize' functions are coming from, and they aren't needed.


n = 5;
[b, a] = butter (n, [100/22050, 1000/22050]);
freqz (b, a, 4096, 44100);
ax = findall (gcf, 'type', 'axes');
set (ax, 'xlim', [20 4000]);
set (ax, 'xscale', 'log');
subplot (2, 1, 1);
set (gca, 'ylim', [-35 3]);


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