# [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

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:
http://en.wikipedia.org/wiki/Wavelet
http://en.wikipedia.org/wiki/Morlet_wavelet

and then go to some more sophisticated literature ;)

Best,
Jörn

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

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

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