From: "Yi Cao" <y.cao@cranfield.ac.uk>
Path: news.mathworks.com!newsfeed-00.mathworks.com!webcrossing
Newsgroups: comp.soft-sys.matlab
Subject: Re: How to zoom into a certain part of FFT?
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Date: Thu, 28 Jun 2007 14:26:46 -0400
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Vista wrote:
>
>
> Hi folks,
>
> This is not a joke post. I really have this question in my mind for
> long
> time.
>
> When I truncate/extract out F(w) for w in [-B, B] and use step size
> deltaB
> to sample it and then do IFFT, what is the portion of f(t) I see?
> Say f(t)
> for t in [a, b]. What are a and b?
>
> Now suppose I find there is some fine structure in [c, d], which is
> shown
> from the visual display of f_hat(t), t in [a, b]. And
a<c<d<b.
>
> How to do IFFT targeting at f(t) on [c, d] with higher resolution?
>
> And so on and so forth?
>
> Thanks!
>
>
If you want to know relations between F(w) and f(t), here it is:

The bandwidth of F(w), [0, B] determines the sample rate in f(t),
i.e. 2B (in Hz) = 1/T (in second); The numer of samples of F(w) in [0
B] equals the number of samples of f(t) in [0 tf] after IFFT; Then,
tf, the time range of f(t) can be determined from T and number of
samples.

hth
Yi