MATLAB: How to calculate center frequency

frequencyscalewavelet

hi all,

I am new for matlab in using continuous wavelet transform. Matlab has provided the centfrq function for calculating the center frequency. However, what is the algorithm? I have checked the code, it seems that the wavemngr and feval functions are used. However, I am not sure how these two function works, especially the feval function, the source code is not public. Can anyone know about the algorithm used in matlab for calculating the center frequency by using the given scale? Thanks.

Best Answer

centfrq determines the peak frequency in Fourier transform of the wavelet which is the center frequency, then for increasing scales the center frequency is

cf/(a*dt) where cf is the center frequency (for the specified wavelet), a is the scale and dt is the sampling interval

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MATLAB: On which frequency i should apply DWT (wavelet transform), sampling frequency or output bandwidth

If your sampling frequency is 128 Hz, then the approximate frequency bands in the DWT are already determined by the sampling frequency.

They are: (Scaling filter band on left, wavelet filter band on right)

[0 32] [32 64] Hz

[0 16] [16 32] Hz

[0 8] [8 16] Hz

[0 4] [4 8] Hz

and so on.

You notice that the band 2-43 Hz is best localized (but certainly not perfectly) in the 1st level approximation coefficients.

What not just use a good filter if you are just using the DWT to perform a frequency-filtering of your signal?

MATLAB: Wavelet bandwith, centre frequency

Hi Chris, there are a couple things you can do:

1.) If you want to see the support of wavelets at different scales, you can input a shifted Kronecker delta sequence

x = zeros(1000,1);
x(500) = 1;
cfs = cwt(x,1:2:64,'sym8');
% next part obviously not needed
for nn = 1:32
plot(cfs(nn,:)); pause(0.2);
end

2.) The other thing is that the Wavelet Toolbox now has a DFT-based continuous wavelet transform, implemented in cwtft.m and an inverse CWT in icwtft.m. The wavelets supported in cwtft have their Fourier transforms explicit. See the reference page for cwtft.m

Also see:

http://www.mathworks.com/help/toolbox/wavelet/ug/bs2gc05-1.html

for some examples.

Best Answer

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MATLAB: On which frequency i should apply DWT (wavelet transform), sampling frequency or output bandwidth

MATLAB: Wavelet bandwith, centre frequency

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