[Eeglablist] timef winsize and padratio variables

[Sarnthein Johannes]

Hi Brian,
 
indeed: 
in fft(tmpX,g.padratio*g.winsize)
the FFT window used is equal to g.winsize*g.padratio.
You can confirm that by looking at the frequency resolution deltaF.
 
Best,
Johannes
 
 
 

________________________________

Von: eeglablist-bounces at sccn.ucsd.edu
[mailto:eeglablist-bounces at sccn.ucsd.edu] Im Auftrag von Brian Roach
Gesendet: Montag, 18. September 2006 17:21
An: eeglab_maillist
Betreff: [Eeglablist] timef winsize and padratio variables


Dear EEGlab users,

I have a question about a few optional input arguments to the timef
function in eeglab.  In the timef.m file, where the matlab fft function
is called, the usage is fft(x,n) where x is an array equal to all the
frequencies at a particular time point (we are looping through
1:timesout) and n is equal to the padratio * the fft window size
(winsize).  The actual line of code is:
tmpX = fft(tmpX,g.padratio*g.winsize);

I am wondering, does the padratio actually increase the size of the fft
window?  The comments from

>>help fft

imply that the second argument in fft(x,n) is the window size.  This
would mean that the FFT window used by timef is not actually equal to
the winsize, but the winsize*padratio.  That can be a big difference,
depending on how large the padratio.  Is that actually true?  If so, why
does the command line spit out "results are oversampled N times" where N
= padratio?  Are the results actually oversampled or is the FFT window
size just that much larger?  I understand that the larger the padratio,
the more frequency output bins returned (and the smaller these are), but
if the padratio does not just make the fft window larger, what is it
doing and why would it not always be set to 1?

thanks,
Brian 

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