[Eeglablist] .datspec freq bins and epoch size

[Steven Pillen]

So there's no way to get smaller frequency windows with an epoch size that
small?


On Wed, Sep 11, 2013 at 5:56 PM, Mikołaj Magnuski <imponderabilion at gmail.com
> wrote:

>
> 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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