[Octave-bug-tracker] [bug #45807] problem with specgram function

[Ernotte Pierre]

URL:
  <http://savannah.gnu.org/bugs/?45807>

                 Summary: problem with specgram function  
                 Project: GNU Octave
            Submitted by: ernottep
            Submitted on: Fri 21 Aug 2015 01:59:35 PM GMT
                Category: Octave Function
                Severity: 3 - Normal
                Priority: 5 - Normal
              Item Group: Incorrect Result
                  Status: None
             Assigned to: None
         Originator Name: ernottep
        Originator Email: 
             Open/Closed: Open
         Discussion Lock: Any
                 Release: 3.8.1
        Operating System: GNU/Linux

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Details:

The following code give a bad result found as attached field:

x = chirp([0:0.001:2],0,2,500);#freq. sweep from 0-500 over 2 sec.
Fs=1000;            # sampled every 0.001 sec so rate is 1 kHz
step=ceil(20*Fs/1000);    # one spectral slice every 20 ms
window=ceil(100*Fs/1000); # 100 ms data window
specgram(x, 2^nextpow2(window), Fs, window, window-step);

************************************************************
I obtain the same result with the following code:

[S,f,t]=specgram(x, 2^nextpow2(window), Fs, window, window-step);
S=abs(S);
figure;imagesc(t,f,S)

*************************************************************
I obtain the good result with the code 

figure;imagesc(S)

*************************************************************
I use signal-1.3.2



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File Attachments:


-------------------------------------------------------
Date: Fri 21 Aug 2015 01:59:35 PM GMT  Name: specgram_bug.pdf  Size: 5kB   By:
ernottep

<http://savannah.gnu.org/bugs/download.php?file_id=34687>

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