Re: [Tftb-help] RE: Tftb-help Digest, Vol 2, Issue 5

[Eric Chassande-Mottin]

Hi,

> Is there anybody could help to explain tfrstft?why using frequency smoothing 
> window H, instead of time smoothing window based on the STFT time-domain 
> equation?

TFRSTFT Short time Fourier transform.
        [TFR,T,F]=TFRSTFT(X,T,N,H,TRACE) computes the short-time Fourier
        transform of a discrete-time signal X.
        X     : signal.
        T     : time instant(s)          (default : 1:length(X)).
        N     : number of frequency bins (default : length(X)).
        H     : frequency smoothing window, H being normalized so as to
                be  of unit energy.      (default : Hamming(N/4)).

I think you are misled by the termilogy of the above online help. the 
input parameter H of tfrstft is the analysis window in the _time_ domain. 
In fact, the terms of the online help of tfrsp should be used here 
instead, namely

       H     : analysis window, H being normalized so as to
                be  of unit energy.      (default : Hamming(N/4)).

I guess the words "frequency smoothing" were meant here to explain that 
this window produces some kind of smoothing in the frequency domain.

see http://gdr-isis.org/tftb/tutorial/node22.html

I'll fix the CVS version if agreed by all developers.

> And why choose the window size as /4?

i think that it is an arbitrary choice. by experience, it gives reasonable 
in many practical cases.

eric.