Re: [Tftb-help] Newbie, want to perform a (probably) very simple task

[Eric Chassande-Mottin]

hi Thomas,

it is unclear which information exactly you want to extract from your 
signal. anyway, to get a time-frequency image of your signal, you can 
either adapt example 2 which uses a Wigner-Ville TF representation.
but it is perhaps simpler to consider short-term Fourier transform which
a straighforward extension of the Fourier transform, see

http://gdr-isis.org/tftb/tutorial/node21.html

and here :

http://cvs.savannah.gnu.org/viewcvs/*checkout*/tftb/tftb/README?rev=HEAD&content-type=text/plain

for an example with GNU Octave.

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you can freely unsubscribe once you know what you want.

eric.

> Here is my problem. I have an arithmetical integer sequence in which
> I suspected to be some periodical information. At a low level (C and fortran)
> I performed some classical DFT manipulations and found a nice spectrum where
> significant information is at some very precise easy to recognize
> rational frequencies (like .33333333... or .20000000 or .199999999).
> But obviously the signal isn't constant in the "time": frenquencies are
> constant, but coefficients of the DFT become greater with "time".
> What I want is to make some decomposition of each frequency in order
> to see what my sequence is made with.
> Thus I launched octave and typed what is on the web page above.
> Since this web page tells what to type for the two initial steps, I did
> it and saw exactly what was expected (I only had to change the value
> concerning the size of the discrete sequence). The plot for the spectrum,
> as expected, shows very well my various interesting frequencies. But
> I really don't understand what I have to type for using and plotting
> the analysis (in the web page, it is with tfrpwv byt maybe another
> algorithm would be also good).
>
> Precisions, my sequence has a length 65536;
> only integers are in it.
> For instance I want to study frequency corresponding to 1/3.
>
> Could someone help me to go further, then I think one I will have understood,
> I will be able to do by myself. As I told it, I am also a newbie at
> Matlab/Octave...
>
> Regards,
>
> --
> Thomas Baruchel
>
>
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