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<div id="divRpF252957" style="direction: ltr;"><span style="font-family: Tahoma; font-size: 10pt;">Hi everyone,</span></div>
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<p class="MsoNormal">When I plot spectral data from continuous EEG, the resulting Power-by-Frequency graph looks very strange. Specifically, starting at about 5 Hz and continuing on to higher frequencies, the plots for each channel have a repeating triangular,
or sawtooth-like, or zig-zag shape.</p>
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<p class="MsoNormal">Here is a Dropbox link to an image of representative data: <a href="https://www.dropbox.com/s/lddxgzlti9m20vj/FFT_triangle_pattern.JPG" target="_blank">https://www.dropbox.com/s/lddxgzlti9m20vj/FFT_triangle_pattern.JPG</a><span style="font-size: 10pt;"> </span></p>
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<p class="MsoNormal">It looks like some kind of wacky filter has been applied, but the only filter in the processing pipeline is a very conventional 0.16-100 Hz bandpass.
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<p class="MsoNormal">The problem isn't a feature of the raw data itself, because opening the same continuous data in different EEG analysis programs and applying a FFT produces very normal looking spectra. This happens across different versions of EEGLAB,
Matlab, and Windows. </p>
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<p class="MsoNormal">The continuous data were recorded using a Biosemi system and saved in .bdf format.</p>
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<p class="MsoNormal">Has anyone run into this before? I’d be very grateful for any suggestions. </p>
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<p class="MsoNormal">Thanks! </p>
<p class="MsoNormal">Pete</p>
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