A newbie's question on Fourier using freqanalysis_mtmfft

[Katya Vinnik]

Dear Anette,

If you are looking at the steady state response and are interested in its
power only, you should not try to achieve the highest frequency resolution,
but rather adjust the parameters (sampling rate and NFFT) to place your SSR
frequency exactly in the center of the frequency bin, which may be rather
large (around 1 hz).

In this way you'd be sure you're capturing all the power coming from from
the SSR and will be able to compare this frequency bin between conditions or
to the nearby frequency bins.

Katya


2009/12/17 Anette Giani <anette.giani at tuebingen.mpg.de>

>  Dear all,
>
> I am a beginner on MEG and I have some basic questions on Fourier
> transformation using the function freqanalysis_mtmfft. It would be great
> if you could help me!
>
>
>
> We are interested in Steady State Responses. Therefore we recorded data 60
> seconds trials.
>
> To transform the time domain into a frequency spectrum we used the function
> freqanalysis_mtmfft. However, I am not sure which value cfg.tapsmofrq.
> Since we would like to have the highest frequency resolution possible I set
> cfg.tapsmofrq to 0.25; the lowest value possible. Do you think that was a
> good choice? Further, does this value mean that our lowest possible
> frequency resolution would be 0.25? If that was the case, how could I avoid
> all smoothing?
>
>
>
> Second, do you think that it would be useful to pad the signal with zeros
> to artificially increase the frequency resolution? I guess this could be
> done using cfg.pad?
>
>
>
> Lastly, an even more general question: What do you think would be handier:
> (1) Compute the frequency spectrum over 60 seconds, to get a high frequency
> resolution or (2) to cut the signal into e.g. 4 second pieces and to average
> all spectra to increase the signal to noise ratio?
>
>
>
> Thanks a lot in advance for your help,
>
>  Anette
>
>
>
> ----------------------------------
>
> The aim of this list is to facilitate the discussion between users of the
> FieldTrip toolbox, to share experiences and to discuss new ideas for MEG and
> EEG analysis.
>
> http://listserv.surfnet.nl/archives/fieldtrip.html
>
> http://www.ru.nl/fcdonders/fieldtrip/
>



--
Ekaterina Vinnik, MD, PhD
Tactile Perception and Learning Lab
Cognitive neuroscience sector,
SISSA,
Trieste,
Italy

+393347032225
lulswinnik at gmail.com

----------------------------------
The aim of this list is to facilitate the discussion between users of the FieldTrip  toolbox, to share experiences and to discuss new ideas for MEG and EEG analysis. See also http://listserv.surfnet.nl/archives/fieldtrip.html and http://www.ru.nl/neuroimaging/fieldtrip.
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