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

 From: jocelyn lu Subject: RE: FW: Re: [Tftb-help] RE: Tftb-help Digest, Vol 2, Issue 5 Date: Sun, 23 Apr 2006 08:56:20 +0800

```Hi,
```
I'm wondering how to recover the signal from your tfrstft?It seems not simple as just using ifft function.
```
TQ,
Joc

```
```From: "jocelyn lu" <address@hidden>
Subject: FW: Re: [Tftb-help] RE: Tftb-help Digest, Vol 2, Issue 5
Date: Sat, 22 Apr 2006 11:00:23 +0800

Hi, Eric,
Sorry, one more doubt,
=> tfr(indices,icol)=x(ti+tau,1).*conj(h(Lh+1+tau));

```
but in equaton of the defination of STFT, http://gdr-isis.org/tftb/tutorial/node22.html, it should be x(u)h*(u-t). I'm not sure how you make the codes tally with the eqn.Kindly advise.
```
Thanks,
Jocelyn

```
```From: "jocelyn lu" <address@hidden>
Subject: Re: [Tftb-help] RE: Tftb-help Digest, Vol 2, Issue 5
Date: Sat, 22 Apr 2006 09:57:10 +0800

Hi,Eric,

```
Thank you very much.I'm very surprised that your group's response so fast and responsible.
```I have two more doubts actually:
1) => tau=-min([round(N/2)-1,Lh,ti-1]):min([round(N/2)-1,Lh,xrow-ti]);
why to choose the tau range like above?how to think it in this way?
2) =>indices= rem(N+tau,N)+1;
```
Is this row index correct in such way to be defined by tau range? Because I found that all the tfr value(before fft) falls on the top and the bottom area of the time-freq domain.Or other words, all zero values in the middle area. You can test it by disable all the codes below
```=> tfr(indices,icol)=x(ti+tau,1).*conj(h(Lh+1+tau));
=> end;

then in Matlab command window, you could enter:
=>X=fmlin(128); tfr=tfrstft(X);imagesc(abs(tfr));

```
I hope you get the same plot result as mine, components seperately located on the top and bottom. Do you think all the signal values transformed by stft?
```A nice fmlin signal is only obtained by doing fft(tfr).
```
I'm wondering why to implement in such way?Besides practical cases, is there any other reason, like math method, or others?
```
thanks,
Jocelyn

```
```From: Eric Chassande-Mottin <address@hidden>
Subject: Re: [Tftb-help] RE: Tftb-help Digest, Vol 2, Issue 5
Date: Fri, 21 Apr 2006 13:58:24 +0200 (CEST)

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.
```
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