Strange spectopo shape

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Violet
Posts: 2
Joined: Thu Sep 17, 2015 8:29 pm

Strange spectopo shape

Post by Violet » Thu Sep 17, 2015 8:41 pm

Hi
I am new user of Biosemi and eeglab. My data shows strange shapes when are imported and plotted with eeglab. As it is shown in the attached image, the spectopo have a high power on low frequencies (1 to 6 Hz) and a very low power on frequencies from 6 Hz and above. These higher frequencies shows a very strange peaks at each 4 Hz intervals (10, 14, 18, 22 Hz, etc).
What could be the origin of this effect?
Attachments
Captura de pantalla 2015-09-17 16.33.59.png
Captura de pantalla 2015-09-17 16.33.59.png (42.46 KiB) Viewed 6114 times

Coen
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Joined: Fri Mar 26, 2004 7:00 pm
Location: Amsterdam, Netherlands
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Re: Strange spectopo shape

Post by Coen » Fri Sep 18, 2015 11:00 am

Not a proper window applied in your FFT routine, see https://en.wikipedia.org/wiki/Window_function.

Best regards, Coen (BioSemi)

Violet
Posts: 2
Joined: Thu Sep 17, 2015 8:29 pm

Re: Strange spectopo shape

Post by Violet » Wed Sep 23, 2015 2:12 am

Thank you so much

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