[FieldTrip] Time-frequency analysis

[jan-mathijs schoffelen]

Dear Kenji,

In addition of applying the fft on the data, fieldtrip normalises the fft with a number that equals 2/Nsmp, where Nsmp is the length of the wavelet.

Best wishes,

Jan-Mathijs

 
On Aug 15, 2011, at 11:00 PM, Kenji Kirihara wrote:

> Dear FieldTrip mailing list members,
> 
> I am interested in time-frequency analysis of EEG and have 
> a question about ft_freqanalysis. I applied ft_freqanalysis to 
> my data for time-frequency analysis using wavelets. Power at each 
> time-requency point is calculated. However, power at each point 
> seems to be too large. For example, power at 4 Hz, 0 ms, O2 is 1218, 
> power at 10 Hz is 730, and power at 20 Hz is 94. These values seem 
> to be too large compared to power calculated using FFT for frequency 
> analysis. I would be grateful if someone tells me why this happens.
> 
> Sincerely,
> 
> Kenji Kirihara
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Dr. J.M. (Jan-Mathijs) Schoffelen 
Donders Institute for Brain, Cognition and Behaviour, 
Centre for Cognitive Neuroimaging,
Radboud University Nijmegen, The Netherlands
J.Schoffelen at donders.ru.nl
Telephone: +31-24-3614793