Re: fft and wavelets

[Sergei Steshenko]

--- On Thu, 8/23/12, Rudolf Widmer-Schnidrig <address@hidden> wrote:

> From: Rudolf Widmer-Schnidrig <address@hidden>
> Subject: Re: fft and wavelets
> To: address@hidden
> Date: Thursday, August 23, 2012, 3:09 AM
> On 23.08.12 11:32, Sergei Steshenko
> wrote:
> > --- On Wed, 8/22/12, Rick T <address@hidden>
> wrote:
> >
> > From: Rick T <address@hidden>
> > Subject: fft and wavelets
> > To: address@hidden
> > Date: Wednesday, August 22, 2012, 7:21 PM
> >
> > Greetings All
> >
> > I can use fft to get the, frequencies, phases and
> magnitude of a loaded 1 second audio file of person saying
> "ahhhh" and recreate it.
> > What I'm trying to do now is find out where each of
> those frequencies begin and where they stop in the 1 second
> audio file
> >
> >
> >
> > Example:100hz starts at .23seconds to .34seconds,
> > 104.34hz starts at .35seconds and ends at .37seconds.
> >
> > Can fft's do this or do I need to shift my whole
> program to use wavelets?  Also are there any wavelet
> examples in octave that show how do this?
> >
> >
> >
> > I'm using Ubuntu Linux 12.04 and Octave 3.2.4 from the
> repo's
> >
> > Thanks
> > Rick
> >
> >
> > -----Inline Attachment Follows-----
> >
> > _______________________________________________
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> >
> >
> > http://www.gnu.org/software/octave/doc/interpreter/Signal-Processing.html#doc-fft
> -> stft (short time Fourier transform).
> >
> >
> > Regards,
> >    Sergei.
> >
> > _______________________________________________
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> >
> 
> Dear Sergei,
> 
> what you are trying to do violates the uncertainty principle
> of the 
> Fourier transform.
> This uncertainty principle states that the product of the
> resolution in 
> the time domain and the frequency domain is some constant.
> If you 
> increase one you necessarily decrease the other.
> 
> Short time Fourier transforms and wavelets are just
> different ways of 
> making a compromise between the two end member cases of
> perfect time 
> resolution that you have in the time series and the perfect
> frequency 
> resolution that you have in the Fourier spectrum.
> 
>                
>            -Ruedi
> 
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> Help-octave mailing list
> address@hidden
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> 


I am not trying to do anything.

Since _short_ time FTT is applied _multiple_ times, each time to a different 
portion of input sequence, spectrum produced by short time FFT depends on time. 
That it, each short time FFT session produces different spectrum.

I do not understand what caused you to explain me uncertainty principle - I 
made no claim regarding time/frequency resolution.

Regards,
  Sergei.