[Mne_analysis] Power peak at 38 Hz?

[Eric Larson]

Can you try the same analysis without the resampling step? Maybe there is
some aliasing of a line harmonic. How did you resample?

You can also try raw.plot_psd to see if the original unprocessed data has
it. That will tell you if something is in the original data, or if there is
a processing problem.

Eric

On Sep 4, 2016 9:12 AM, "Nico Adelhöfer" <nico.adelhoefer at st.ovgu.de> wrote:

> Hello,
>
> this question is not really related to MNE itself, but maybe someone has
> seen something like this before (I am new to EEG analysis):
>
> I did a fast Fourier transform on 6 second long segments and calculated
> mean power values (averaged over electrodes, participants and 15 segments
> each). What perplexes me is the power peak at approx. 38 Hz:
>
>
>
> My steps for data preparation were as follows:
>
>    1. band-pass filter of data (1 to 45 Hz)
>    2. resampling from 512 Hz to 200 Hz
>    3. cut recording into consecutive segments of 6 sec duration
>    4. exclude segment if maximum allowed voltage step of 50 µV is exceeded
>    5. exclude segment if activity is lower than 0.5 µV
>    6. exclude segment if maximum and minimum amplitude exceed +/- 200 µV
>    7. exclude segment if maximum absolute difference of values in the
>    segment > 200 µV
>    8. retain only segments that are ok for all electrodes
>    9. randomly choose 15 such good segments (all electrodes) from every
>    participant
>    10. calculate FFT for every 2 sec time segment for every electrode and
>    participant
>    11. calculate mean of all these FFTs
>    12. plot
>
> Has someone seen a similar peak before?
>
> Thanks for any help and advice.
>
> Nico
>
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