freqanalysis_wltconvol.m

[Brian Roach]

Dear FieldTrip users,

I have been playing with the freqanalysis_wltconvol function in hopes of
using the morlet wavelet time frequency analysis on some eeg data.  I have
been able to get it running, and I find that it works very quickly, which
is great.  However, I am hoping some users or F.T. programmers can explain
some of the function inputs and processing.  The cfg example is as follows:

% cfg.method         = 'wltconvol';
% cfg.foi            = 1:1:100;
% cfg.width          = 7;
%  or
% cfg.width          = linspace(5,10,length(cfg.foi));
% cfg.toi            = 0:0.1:2;
% cfg.gwidth         = 3;

I believe that the cfg.width specifies the number of wave cycles used in
each frequency's wavelet analysis (so at 2Hz, 7 cycles spans 3500ms of
data, right?).  Maybe this is not correct, because I do not seem to get the
frequencies as low as I would expect given my data epoch length.  Perhaps
this has to do with the cfg.gwidth parameter, which I do not think I
completely understand - what is it?

Also, we do not have the matlab wavelet toolbox, and it appears that it is
not required, but how is the morlet wavelet implemented?  As I look through
the code I see calls to fft, ifft, and fftshift, but I wonder how I can
give a good technical description of this process if I find results in a
larger data set.

Finally, is there a function or a way to compute the frequency bandwidth
based on the cfg inputs, or is there a fix frequency bandwith for each foi
here?  I am sure I am confusing a number of things here, so no response is
too simple.

Thanks for any advice, please let me know if there is more information I
can give or if I can clarify my questions.

Brian
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://mailman.science.ru.nl/pipermail/fieldtrip/attachments/20060929/2105af15/attachment-0001.html>