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From: "Vista" <abc@gmai.com>
Newsgroups: comp.soft-sys.matlab
Subject: Re: How to zoom into a certain part of FFT?
Date: Thu, 28 Jun 2007 19:01:19 -0700
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"Yi Cao" <y.cao@cranfield.ac.uk> wrote in message 
news:ef5bd15.13@webcrossing.raydaftYaTP...
> 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

Thanks. If you want [c, d] in the time domain, not [0, tf], how to do it?

Btw, I am not sure how the "0" (the left boundary) is determined?