[Eeglablist] .datspec freq bins and epoch size

[Steven Pillen]

That is, without interpolation  (which probably isn't ideal for the kind of
things I'm trying to see)?


On Fri, Sep 13, 2013 at 11:02 AM, Steven Pillen <stevendpillen at gmail.com>wrote:

> 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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>>
>
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