[Octave-bug-tracker] [bug #53855] [signal] butter filter with strange results

[Renato]

URL:
  <http://savannah.gnu.org/bugs/?53855>

                 Summary: [signal] butter filter with strange results
                 Project: GNU Octave
            Submitted by: yamane
            Submitted on: Mon 07 May 2018 10:07:04 AM UTC
                Category: Octave Forge Package
                Severity: 3 - Normal
                Priority: 5 - Normal
              Item Group: Incorrect Result
                  Status: None
             Assigned to: None
         Originator Name: 
        Originator Email: 
             Open/Closed: Open
         Discussion Lock: Any
                 Release: 4.4.0
        Operating System: Any

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Details:


%=== example of the code ===
n=5;
typenoise = noise(60*44100, 1, 'pink');

[b,a] = butter(n, [100/(22050), 1000/(22050)]);
filtered = filter(b, a, typenoise);
normalized = normalize(filtered, 'wav');
audiowrite ('test.wav', normalized, 44100);

freqz(b, a, 4096, 44100);
ax = findall(gcf, 'Type', 'axes');
set(ax, 'XLim', [20 4000]);
set(ax, 'YLim', [-35 3]);
set(ax, 'XScale', 'log');
%=============================


When n<=4, the result in low-frequency is OK.
When n >=5, the result in low-frequency is strange.



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File Attachments:


-------------------------------------------------------
Date: Mon 07 May 2018 10:07:04 AM UTC  Name: n5.png  Size: 10KiB   By: yamane

<http://savannah.gnu.org/bugs/download.php?file_id=44109>

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