[Eeglablist] Problem with inverse transform

[Richards, John]

Try cwt and icwt in matlab.  cwt is "continuous wavelet transform" and gives the weights for the time-frequency function;  cwt without arguments produces the "scalogram".   icwt takes the cfs and f from [cfs f]=cwt..  and can extract frequency-band inverse transform data.  My understanding is that wavelet frequency decomposition has positive properties compared with fft and ifft, and over typical EEG/ERP bandpass filters.

John

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John E. Richards
Carolina Distinguished Professor
Department of Psychology
University of South Carolina
Columbia, SC  29208
Dept Phone: 803 777 2079
Fax: 803 777 9558
Email: richards-john at sc.edu
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-----Original Message-----
From: eeglablist <eeglablist-bounces at sccn.ucsd.edu> On Behalf Of Makoto Miyakoshi via eeglablist
Sent: Thursday, August 3, 2023 4:14 PM
To: Franziska Kirsch <franziska.kirsch at ovgu.de>
Cc: eeglablist at sccn.ucsd.edu
Subject: Re: [Eeglablist] Problem with inverse transform

Dear Franzi,

I did not know there is such a thing as inverse short-term Frourier Transformation, but I can see it should work.
First of all, you have to share the error message so that we can guess the cause of the problem better.
That said, judging from your comment,

> Also, I'm not sure if the input requires complex data or data already
transformed to power.

most likely you did not understand the required input type and your input was wrong. The input must be 3-D complex data. See this page. Note 'Input arguments' can be found AFTER 'Examples' (strange!)
https://urldefense.com/v3/__https://www.mathworks.com/help/signal/ref/istft.html*mw_df6a90fa-0796-411d-ab9c-d86cc3c0edec_sep_mw_f4653206-42e2-4878-82ba-66875c98c86c__;Iw!!Mih3wA!H7QLYv7nSTdwJrG_4fGNP0eV4b4XW-NVNWLV872UQPC3mzT29zQNAnKNKSA54Svi0sLM59alPwfeIRPh0nYfPq0nHpw$

Good luck!

Makoto

On Fri, Jul 28, 2023 at 8:30 PM Franziska Kirsch via eeglablist < eeglablist at sccn.ucsd.edu> wrote:

> Dear List Members,
>
> currently I am trying to inverse transform data in time-frequency
> space back to time domain. I have used the istft - function (inverse
> short time Fourier transform) from Matlab, but it does not seem to
> work. I keep getting error messages about problems with the input
> data, even though it should be correct (as the function says ‚matrix
> with time increasing across the columns and frequency increasing down
> the rows‘). Also, I'm not sure if the input requires complex data or data already transformed to power.
>
> Another idea is to calculate it manually and multiply a complex sine
> wave by the complex Fourier coefficient and sum the results.
>
> Any recommendations on how to achieve an inverse transform? Thank you
> in advance for your help!
>
> Yours sincerely,
> Franzi Kirsch
>
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