A newbie's question on Fourier using freqanalysis_mtmfft

[Ingrid Nieuwenhuis]

Dear Anette,

Cfg.tapsmofrq is an option for multitaper analysis (cfg.taper = 'dpss'),
which might not be what you want if you want high frequency resolution.

I would recommend looking at the tutorial "Time-frequency analysis using
Hanning window, multitapers and wavelets"
http://fieldtrip.fcdonders.nl/tutorial/timefrequencyanalysis there you can
read about the differences between hanning taper and multitapers.

Hope this helps a bit

Best Ingrid

  _____

From: FieldTrip discussion list [mailto:FIELDTRIP at NIC.SURFNET.NL] On Behalf
Of Anette Giani
Sent: Thursday, December 17, 2009 9:48 AM
To: FIELDTRIP at NIC.SURFNET.NL
Subject: [FIELDTRIP] A newbie's question on Fourier using
freqanalysis_mtmfft



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



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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.

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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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