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From: "Steve Amphlett" <Firstname.Lastname@Where-I-Work.com>
Newsgroups: comp.soft-sys.matlab
Subject: Re: Need help with Fourier transform
Date: Wed, 2 Sep 2009 17:59:19 +0000 (UTC)
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Rune Allnor <allnor@tele.ntnu.no> wrote in message <b6dff0b3-e1f3-40c7-bff3-6118dda5a8a3@c37g2000yqi.googlegroups.com>...
> 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
Cycle-by-cycle update perhaps?  Integrators reset.