[Tftb-help] RE: Tftb-help Digest, Vol 4, Issue 9

[jocelyn lu]

HI, Eric,
Thanks.  But why you say "at t=0, half of the right hand part of the 
windowed signal is
> zero", if the signal is assumed to be zero at t<0, then should be left hand 
> side of the windowed signal (when the window is centered at t=0)  is zero 
> at t=0.

Thanks,
Joc


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> Subject: Tftb-help Digest, Vol 4, Issue 9
> Date: 13 Jun 2006 01:42:58 -0700
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>    1. tfrsp doubt (fwd) (Eric Chassande-Mottin)
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> Message: 1
> Date: Tue, 13 Jun 2006 10:38:55 +0200 (CEST)
> From: Eric Chassande-Mottin <address@hidden>
> Subject: [Tftb-help] tfrsp doubt (fwd)
> To: address@hidden
> Message-ID: <address@hidden>
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>
> hi,
>
> your observation is related to finite size effects. we analyze signals of
> finite duration. to compute a TFR, you need to decide what to do at the
> boundaries. most (if not all) routines of the TFTB (including tfrsp)
> assume that the signal is zero beyond the boundaries.
>
> consequently, from the definition of a short-term Fourier analysis,
> http://gdr-isis.org/tftb/tutorial/node34.html the signal selected by the
> analysis window when it is centered around a point near a boundary is
> partly zero. at t=0, half of the right hand part of the windowed signal is
> zero. we see less signal, thus the spectrogram amplitude decreases.
>
> if you are not satisfied by this, you may like to consider TFRs which
> conserves the support of the signal (i.e., which are zero when the signal
> is zero). see Flandrin, Time-frequency/time-scale analysis, Academic Press
> for more details on this point.
>
> bye, e.
>
> ---------- Forwarded message ----------
> Date: Tue, 13 Jun 2006 08:27:52 +0800
> Subject: tfrsp doubt
>
> Hi,Eric,
> I found one probelm in tfrsp.m.
> If I enter:"sig=fmlin(128,0.1,0.4); tfrsp(sig);" in Matlab commend,I get 
> one
> plot as per attached file.
>
> Based on this signal, tfr should be at time 0 ->normalised frequency is 
> 0.1,
> whereas, time 128->freq 0.4.
>
> But how come appear weak energy value at the time 0 and time 128 in the 
> plot?
> Is it dealed properly?How to see the energy value exactly cut at 
> location(0,
> 0.1) and (128, 0.4)?
>
> Thanks,
> Joc
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