A newbie's question on Fourier using freqanalysis_mtmfft

[Anette Giani]

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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