[Eeglablist] .datspec freq bins and epoch size

[Mikołaj Magnuski]

Hi Steven,

Frequency resolution depends on window size, so what you're seeing is
normal.
However, for visualisation purposes you can interpolate the spectrum (which
is implemented by zero-padding your data to some desired length) - EEGlab
functions allow to specify the degree of this smoothing.
For example you can control the zero-padding in spectopo function with
'nfft' (specific length to zero-pad the data to).
By specifying 'nfft' to be two times the number of samples in your analysis
window you increase the frequency resolution twofold (although you have to
remember that this is not a genuine increase in frequence resolution but an
interpolation).

Also, see the help messages to pop_spectopo and spectopo functions.

For time-frequency you can use the 'nfreqs' key in newtimef.m to control
the frequency resolution
 12 wrz 2013 01:27, "Steven Pillen" <stevendpillen at gmail.com> napisał(a):

> Hello, EEGLABlist.
>
> When we ran power spectrum measures through the study functions on files
> whose epochs were about 0.2 seconds long, it looked like the power spectra
> chart generated had very few points of reference.  Looking at the .datspec
> files using the function
> *
> *
> *m = importdata('design1_2003_regular.datspec')*
> *
> *
> in m.freqs, it looked like there was one bin for every 5 hz, which matched
> what the charts looked like.
>
> We ran the same data again, this time cut into 1 second epochs, and the
> power spectra looked like they had many more reference points.  Likewise,
> there appeared to be a bin in m.freqs for every 1 hz. as opposed to the
> previous 5.
>
> Is there any way to increase the number of bins with a smaller sized epoch
> so that the power spectra is more robust?
>
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