[FieldTrip] MOrler wavelet nonconstant Q

"Jörn M. Horschig" jm.horschig at donders.ru.nl
Mon Dec 3 13:55:16 CET 2012

Dear Fanny,

I have no experience in using this nonconstant Q wavelet, but I hope I 
can shed some light on the terminology.

> "
> /Time--frequency analysis was performed for
> each channel by convolving the data with a complex Morlet
> wavelet w(t, f0) having a Gaussian shape in time (?t) and in
> frequency (?f) around the center frequency ( f0). Nonconstant
> wavelets with Q increasing from f0/?f =8.5 to 13 for frequencies
> from 30 to 100 Hz (step size 2 Hz) were used.
> /
> "
> -  I don't understand what is /f/_0 and  ?/_f /

If you compute the frequency spectrum of any signal, you will see some 
peaks in the frequency spectrum. If you compute the frequency spectrum 
of a wavelet, the maximal peak is conventionally called center 
frequency. In Matlab, you can obtain the center frequency by the 
function 'centfrq'. Note that the center frequency also depends on the 
scale of your wavelet.

Any peak can be wide or narrow, and just like in statistics you can 
describe this with the standard deviation. I am not in particular 
familiar with/?f /and the method you are describing, but I would guess 
that it is really just the standard deviation, given that /? /is 
conventionally used to denote the standard deviation.

Judging from your questions, without offending, that you are probably 
new to the field of wavelets, you should probably start off with reading 
more general literature on wavelets. Maybe start off with Wikipedia:

and then go to some more sophisticated literature ;)


Jörn M. Horschig
PhD Student
Donders Institute for Brain, Cognition and Behaviour
Centre for Cognitive Neuroimaging
Radboud University Nijmegen
Neuronal Oscillations Group
FieldTrip Development Team

P.O. Box 9101
NL-6500 HB Nijmegen
The Netherlands

E-Mail: jm.horschig at donders.ru.nl
Tel:    +31-(0)24-36-68493
Web: http://www.ru.nl/donders

Visiting address:
Trigon, room 2.30
Kapittelweg 29
NL-6525 EN Nijmegen
The Netherlands

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