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Frequency Scale in Wavelet Transform
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dsorasak
Dear All,
I am trying to apply continuous wavelet transform to sound data but the periods on y-axis are way off from those resulting from FFT.
I tried to use CWT demo but the problem still existed.
In the attachment, SigL wave is the data to be CWTed. Signal is the original sound file.
Any suggestions?
Best,
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Have you used the /FSCL flag?
I don't think that the mapping between the CWT and frequency analysis via the FFT is very rigorous so some caution is advised.
A.G.
July 18, 2019 at 08:19 am - Permalink
In reply to Have you used the /FSCL flag… by Igor
The flag (/FSCL) has been used. The results were still different. As you said, I should take caution working on CWT. Do you have a proper way to perform the mapping task?
July 23, 2019 at 09:44 pm - Permalink
The reason that I feel uncomfortable with this mapping is that IMO it is completely inappropriate. The conventional notion of frequency applies to periodic basis functions such as sines and cosines. The CWT wavelets do not represent pure frequencies so while I added support for the scaling factor to match its use in the literature, I don't think it is appropriate to display the vertical axis in units of e.g., Hz. In reality, the vertical axis represents wavelet scale. If exact frequency representation is important to you I recommend using the STFT or the WignerTransform.
AG
July 24, 2019 at 12:04 pm - Permalink
In reply to The flag (/FSCL) has been… by dsorasak
Dear Sorasak Danworaphong
I have experienced some problems about CWT operation command.
One of them is that deltax of source wave should be 1 when use FFT method (/M=0).
All of my experience are described in following article.
https://www.wavemetrics.com/forum/general/question-cwt-operation
July 25, 2019 at 11:30 pm - Permalink
Dear Sorasak Danworaphong
Because frequency is reciprocal to scale parameter and y-axis of M_CWT is related to the scale, /SMP2=4 and display it by log-axis is suitable.
See the attachment file which was calculated from your file using following macro codes.
In order to decrease the file size some waves and objects are deleted.
July 29, 2019 at 01:14 am - Permalink