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From:  Luna Moon <lunamoonmoon@gmail.com>
Newsgroups: comp.dsp,comp.soft-sys.matlab
Subject: Re: how to use IFFT to reconstruct signal in a specific region t in [a, b]?
Date: Sat, 11 Aug 2007 12:46:34 -0700
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On Aug 10, 9:24 am, dspg...@netscape.net wrote:
> On Aug 9, 12:19 am, "Luna Moon" <lunamoonm...@gmail.com> wrote:
>
> > Hi all,
>
> > Let's say by doing IFFT on F(v), which is the spectrum of signal f(t), I was
> > able to reconstruct f(t), for t in [0, T].
>
> > Now I want to ask is there a way to do another IFFT to reconstruct the
> > specific part f(t) for t in [T, 2T], without any waste of previous
> > calculations?
>
> > Basically, I want to ask, if it is possible to use IFFT to reconstruct to
> > any slot t in [a, b] in the time domain for signal f(t)?
>
> > Thanks a lot!
>
> You can use Chirp Z Transform methods to evaluate portions of either
> the frequency or time domain. The CZT is discussed in the O&S books.
>
> Cheers,
> David

Thanks David, is CZT for the following usage?
---------------------
I knew that DFT/FFT assumes the signal is periodic. My question is
related to the window of one such period. Yes DFT/FFT has a focal
window, and everything outside this window is assumed to be periodic
extension of the content within this window. But in a reconstruction
of time-domain signal from spectrum using Inverse FFT/DFT, what is the
default focal window? And how do we shift the focal window? Eventually
I want to be able to slide the window along all the time-domain signal
and focus on one part of the signal at a time.

How to do that? Thanks a lot!