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 Wavelet scale to frequency		  New Topic  Reply to Topic
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misi2096

3 Posts
Posted - 12/16/2012 :  1:11:29 PM  Show Profile  Edit Topic  Reply with Quote  View user's IP address  Delete Topic
Hello!

I want to analyze the time-frequency domain of evoked potential oscillations from EEG data with continuous wavelet transform. More specifically I would like to plot it like time (basically timepoints) on X-axis and frequency (pseudo-frequency) in Hz on Y-axis.

Can you tell me how to convert Morlet wavelet scales to frequencies? According to MATLAB documentation I would have to know the central frequency (sometimes referred to as center freq.) of the Morlet wavelet to be able to compute the pseudo-frequencies table.
MATLAB states, that the formula is: ps.F = centr.F / ( scale * sampl.period) and for MATLAB's built in Morlet wavelet it states central frequency as 0.8125.

Here you can see the mismatch:





I've read the English documentation but I still don't understand what the "Wave number" parameter stands for when using Morlet wavelets. Does it have something to do with the desired central frequency?


Thank you in advance!

misi2096

3 Posts
Posted - 12/16/2012 :  1:14:44 PM  Show Profile  Edit Reply  Reply with Quote  View user's IP address  Delete Reply
I'm sorry, I forgot to mention, sampling frequency is 5000 Hz therefore sampling period is 1/5000 = 0.0002
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Penn

China
644 Posts
Posted - 12/17/2012 :  02:11:16 AM  Show Profile  Edit Reply  Reply with Quote  View user's IP address  Delete Reply
Hi,

Currently, Origin 9.0 SR1 (or earlier version) does not provide the way to generate the pseudo-frequencies from scales. However, there is already a plan (ID is ORG-5373) to add support for such functionality.

Penn
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misi2096

3 Posts
Posted - 12/17/2012 :  02:30:54 AM  Show Profile  Edit Reply  Reply with Quote  View user's IP address  Delete Reply
I see, but can you tell me what the Wave number parameter stands for in the Analysis -> Signal processing -> Wavelet -> Continuous wavelet window when using Morlet wavelet? It is mentioned here also: http://www.originlab.com/www/helponline/Origin/en/programming/mergedProjects/X-Function/X-Function/Cwt.html#Variables

Or can you tell me where did you implant the continuous wavelet analysis feature?

Thank you in advance!
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Penn

China
644 Posts
Posted - 12/17/2012 :  05:03:10 AM  Show Profile  Edit Reply  Reply with Quote  View user's IP address  Delete Reply
Hi,

You can refer to this page for more details about the wave number.

Penn
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Hideo Fujii

USA
1582 Posts
Posted - 04/21/2015 :  10:24:14 AM  Show Profile  Edit Reply  Reply with Quote  View user's IP address  Delete Reply
For visitors to this thread,

The above link in Penn's post has been changed to:

http://www.originlab.com/doc/Origin-Help/Continuous-WaveTrans
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