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

From: François AUGER
Subject: Re: [Tftb-help] Help, why 'morlet' and 'a' expressions are of this form in tfrscalo?
Date: Fri, 11 Mar 2011 09:27:22 +0100

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

Neuropsychology and Applied Cognitive Neuroscience (NACN) Lab
Institute of Psychology
Chinese Academy of Sciences
Beijing 100101
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