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From: Rune Allnor <allnor@tele.ntnu.no>
Newsgroups: comp.soft-sys.matlab
Subject: Re: Need help with Fourier transform
Date: Wed, 2 Sep 2009 09:38:32 -0700 (PDT)
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On 2 Sep, 16:46, "Steve Amphlett" <Firstname.Lastn...@Where-I-
Work.com> wrote:

> If I want to track single frequencies, I can write code like this:
...
> So I can recover the amplitudes of the real and imag components in my fake signal with the summations.  But what about the wiggles in the plots?

...so what you do is to use an integrator to accumulate
the energy of each nominal frequency band...?

One effect that contributes to the wiggles is the cross-talk
between the crequency components. Umless the two sines are
orthogonal, they will interact with a coupling factor that is
given by the sinc window function at any given N.

And since N varies all the time - if I understand your code
correctly - the coupling factor also changes all the time,
switching between positive and negative, and sliding further
and further apart in spectrum domain.

Rune