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</o:shapelayout></xml><![endif]--></head><body lang=DA link=blue vlink=purple><div class=WordSection1><p class=MsoNormal><span lang=EN-US>Dear all,<o:p></o:p></span></p><p class=MsoNormal><span lang=EN-US><o:p> </o:p></span></p><p class=MsoNormal><span lang=EN-US>I have been trying to plot the spectra of an EEG register (raw data) with “Plot-> Plot spectra and maps”, which uses the pwelch function. The register was sampled at 512 Hz, saved on a cnt file and imported using the ANT plugin (v1.09). I selected a 100% of data to sample and a frequency range of 0 to 256 Hz to plot. For the topoplot() function I used the default options (according to the Command window it uses: windows length 512, fft length 1024, overlap 0)<o:p></o:p></span></p><p class=MsoNormal><span lang=EN-US>I found out that the PSD plot showed a response more similar to the Hamming window than the PSD of the signal. Even changing the overlap the response was the same or even worse. <o:p></o:p></span></p><p class=MsoNormal><span lang=EN-US>It turned out that only when putting the same window length and fft length ( 512 and 512, 1024 and 1024, etc.) the PSD function had the shape of a “realistic” recording. Also removing the DC improved a lot the plot.<br>My partner José Biurrun Manresa tried to obtain the PSD without using the EEGLAB interface and I obtained the same results with this register. What really improved the obtained plot was detrending the signal:<o:p></o:p></span></p><p class=MsoNormal><span lang=EN-US><o:p> </o:p></span></p><p class=MsoNormal><span lang=EN-US style='font-family:"Arial","sans-serif"'>plot(10*log10(pwelch(detrend(EEG.data(1,:)))))<o:p></o:p></span></p><p class=MsoNormal><span lang=EN-US> <o:p></o:p></span></p><p class=MsoNormal><span lang=EN-US>Probably would be a good idea to suggest detrending the signal or removing the offset before plotting the spectra of raw data. Any suggestion on this would be great. Thanks in advance.<o:p></o:p></span></p><p class=MsoNormal><span lang=EN-US><o:p> </o:p></span></p><p class=MsoNormal><span lang=EN-US>Best regards,<o:p></o:p></span></p><p class=MsoNormal><span lang=EN-US>Federico Arguissain<o:p></o:p></span></p><p class=MsoNormal><span lang=EN-US><o:p> </o:p></span></p><p class=MsoNormal><span lang=EN-US style='mso-fareast-language:DA'><o:p> </o:p></span></p><p class=MsoNormal><span lang=EN-US style='font-size:9.0pt;color:#1F497D;mso-fareast-language:DA'>----------------------------------------------<o:p></o:p></span></p><p class=MsoNormal><span lang=EN-US style='font-size:9.0pt;color:#1F497D;mso-fareast-language:DA'>Federico Gabriel Arguissain, Ph.D. fellow<o:p></o:p></span></p><p class=MsoNormal><span lang=EN-US style='font-size:9.0pt;color:#1F497D;mso-fareast-language:DA'><o:p> </o:p></span></p><p class=MsoNormal><span lang=EN-US style='font-size:9.0pt;color:#1F497D;mso-fareast-language:DA'>Center for Sensory-Motor Interaction - SMI <o:p></o:p></span></p><p class=MsoNormal><span lang=EN-US style='font-size:9.0pt;color:#1F497D;mso-fareast-language:DA'>Department of Health Science and Technology - HST<o:p></o:p></span></p><p class=MsoNormal><span style='font-size:9.0pt;color:#1F497D;mso-fareast-language:DA'>Aalborg University <o:p></o:p></span></p><p class=MsoNormal><span style='font-size:9.0pt;color:#1F497D;mso-fareast-language:DA'><o:p> </o:p></span></p><p class=MsoNormal><span style='font-size:9.0pt;color:#1F497D;mso-fareast-language:DA'>Fredrik Bajers Vej 7E-1, DK-9220 Aalborg E, Denmark<o:p></o:p></span></p><p class=MsoNormal><span lang=EN-US style='font-size:9.0pt;color:#1F497D;mso-fareast-language:DA'>phone: +45 9940 9762<o:p></o:p></span></p><p class=MsoNormal><span lang=EN-US style='font-size:9.0pt;color:#1F497D;mso-fareast-language:DA'>email: <a href="mailto:fga@hst.aau.dk"><span style='color:blue'>fga@hst.aau.dk</span></a> <o:p></o:p></span></p><p class=MsoNormal><span style='font-size:9.0pt;color:#1F497D;mso-fareast-language:DA'>Skype: federico.arguissain<o:p></o:p></span></p><p class=MsoNormal><span lang=EN-US style='font-size:9.0pt;color:#1F497D;mso-fareast-language:DA'><a href="http://www.smi.hst.aau.dk/"><span lang=DA style='color:blue'>http://www.smi.hst.aau.dk/</span></a></span><u><span style='color:blue;mso-fareast-language:DA'><o:p></o:p></span></u></p><p class=MsoNormal><span style='font-size:9.0pt;color:#1F497D;mso-fareast-language:DA'>---------------------------------------------- </span><span style='color:#1F497D;mso-fareast-language:DA'><o:p></o:p></span></p><p class=MsoNormal><o:p> </o:p></p></div></body></html>