different results in fft of an chirp in matlab and octave

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different results in fft of an chirp in matlab and octave

Dietmar Warning

Dear octave user,

can anybody help me to find out why I get different results by plotting the fft results of a 800 ... 50kHz chirp Signal in matlab and octave.

Please see the attached screenshots and the used script. It looks for me that the behaviour in low frequency end is more reasonable in matlab.

Any hint is appreciated

Dietmar



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matlab_chirp_fft.png (8K) Download Attachment
octave_chirp_fft.png (38K) Download Attachment
test_chirp_fft.m (874 bytes) Download Attachment
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Re: different results in fft of an chirp in matlab and octave

Mike Miller-4
On Wed, Mar 07, 2018 at 14:47:54 +0100, Dietmar Warning wrote:
> can anybody help me to find out why I get different results by
> plotting the fft results of a 800 ... 50kHz chirp Signal in matlab and
> octave.
>
> Please see the attached screenshots and the used script. It looks for
> me that the behaviour in low frequency end is more reasonable in
> matlab.

Yes, this is likely an error in the Octave chirp function with the
"logarithmic" option. It would be very helpful if you could file a bug
with your example showing the difference at
https://savannah.gnu.org/bugs/?group=octave&func=additem

--
mike


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Re: different results in fft of an chirp in matlab and octave

Przemek Klosowski-7

On 03/07/2018 04:33 PM, Mike Miller wrote:
> On Wed, Mar 07, 2018 at 14:47:54 +0100, Dietmar Warning wrote:
>> can anybody help me to find out why I get different results by
>> plotting the fft results of a 800 ... 50kHz chirp Signal in matlab and
>> octave.
> Yes, this is likely an error in the Octave chirp function with the
> "logarithmic" option.
If you look at plots of specgram(ChirpSignal) in Octave and Matlab,
Octave's looks like it spends too much time in the low frequency range.


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Re: different results in fft of an chirp in matlab and octave

Dietmar Warning-2
In reply to this post by Mike Miller-4

Thanks,

for all the response.

I have tried to file a report but I have no account and I am an temporary user of octave.

Sorry, can someone post a bug report. I have used octave 4.2.1 under windows.

Thank you,

Dietmar


Am 07.03.2018 um 22:33 schrieb Mike Miller:
On Wed, Mar 07, 2018 at 14:47:54 +0100, Dietmar Warning wrote:
can anybody help me to find out why I get different results by
plotting the fft results of a 800 ... 50kHz chirp Signal in matlab and
octave.

Please see the attached screenshots and the used script. It looks for
me that the behaviour in low frequency end is more reasonable in
matlab.
Yes, this is likely an error in the Octave chirp function with the
"logarithmic" option. It would be very helpful if you could file a bug
with your example showing the difference at
https://savannah.gnu.org/bugs/?group=octave&func=additem



-----------------------------------------
Join us March 12-15 at CERN near Geneva
Switzerland for OctConf 2018.  More info:
https://wiki.octave.org/OctConf_2018
-----------------------------------------



-----------------------------------------
Join us March 12-15 at CERN near Geneva
Switzerland for OctConf 2018.  More info:
https://wiki.octave.org/OctConf_2018
-----------------------------------------