How to adjust the calculated frequency range in Continuous Wavelet Transforms

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EL 2020-1-9

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评论： David Sokalski 2021-5-4

Hello,

I'm currently sampling a wave at 20,000Hz, with the frequency I'm interested in occuring around 8,000Hz. This works well for FFT, with the output range for frequency occuring between 0 and 10,000Hz. However, using the cwt function, the output results in the range of 0 (or near 0) to 8, 682.5 Hz. I do not understand the math AT ALL behind this, but I assumed since wavelet transform used FFT function 'somewhere' within, I would have an output frequency MAX of 10,000 Hz.

Is there a way to have up to 10,000 Hz output range using cwt?

Thanks!

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David Sokalski 2021-5-4

在 MATLAB Online 中打开

Hey there,

when creating the cwtfilterbank there is a flag called "FrequencyLimits" where you can set a range like so:

fb = cwtfilterbank('SignalLength', your_signal_length,...
    'SamplingFrequency', 20000, ...
    'FrequencyLimits',[500 9000]);

Following the Matlab Documentation you can then plot the result by using:

[cfs,frq] = wt(fb,sig);
t = (0:(your_signal_length - 1)/Fs;
figure;
pcolor(t,frq,abs(cfs))
set(gca,'yscale','log');shading interp;axis tight;
title('Scalogram');xlabel('Time (s)');ylabel('Frequency (Hz)')