Re: [Tftb-help] Help, why 'morlet' and 'a' expressions are of this form in tfrscalo?

[François AUGER]

Dear Ting Xu,

At 03:45 10/03/2011, ting xu wrote:
> Greetings all,
> I am trying to use wavelet method to analyze the brain signal. I 
> found the results from 'tfrscalo' and 'cwt' were different. It is 
> difficult for me to understand the following questions:
> (1) In tfrscalo, the script showed that the morlet wavelet was 
> generated by ha  = 
> exp(-(2*log(10)/nha^2)*tha.^2).*exp(i*2*pi*f(ptr)*tha). Should the 
> morlet be exp(-x^2/2)*cos(5*x)?

I think that exp(-x^2/2)*cos(5*x) is the Mexican hat wavelet, not the 
Morlet Wavelet.

> (2) the scale 'a' and the frequency 'f' have a relationship 
> f=fc*fs/a, here fc is the center frequency of a wavelet, fs is the 
> sampling frequency. But in tfrscalo, f = 
> logspace(log10(fmin),log10(fmax),N), a = 
> logspace(log10(fmax/fmin),log10(1),N), it does not seem to satisfy 
> f=fc*fs/a. I have confused about it.

The dilation factor is adimensional. If you multiply fc by fs, the 
result will be in s^{-2}, and can't be equal to the frequency  f.
I am not sure to be able to understand your question.

Best regards,

> Can anyone help me please? Much appreciate!
>
> Best regards,
> Ting Xu
>
> --
> Xu,Ting
> Postgraduate
> Neuropsychology and Applied Cognitive Neuroscience (NACN) Lab
> Institute of Psychology
> Chinese Academy of Sciences
> Beijing 100101
> China
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Francois Auger,  http://www.univ-nantes.fr/auger-f

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