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Thread Subject:
fft, discontinuity

Subject: fft, discontinuity

From: Giorgia

Date: 24 Aug, 2012 15:17:08

Message: 1 of 4

Hi everyone,
I have to process a signal that is composed of several smaller signals aligned togheter, it may occurs that two consecutive signals create at the border a cusp type discontinuity. Since I have to compute the FFT of the signal, how do you think the presence of a cusp might infect the final result? Do you eventually know if there is a way to predict and eventually correct the problem?

thankyou

Subject: fft, discontinuity

From: Matt J

Date: 24 Aug, 2012 17:28:07

Message: 2 of 4

"Giorgia " <emika@hotmail.it> wrote in message <k185tk$oj1$1@newscl01ah.mathworks.com>...
> Hi everyone,
> I have to process a signal that is composed of several smaller signals aligned togheter, it may occurs that two consecutive signals create at the border a cusp type discontinuity. Since I have to compute the FFT of the signal, how do you think the presence of a cusp might infect the final result? Do you eventually know if there is a way to predict and eventually correct the problem?
===========

Nonsmooth signals tend to have wider spectra. To us bystanders, there's no obvious reason why this is a problem.

Subject: fft, discontinuity

From: Giorgia

Date: 24 Aug, 2012 17:49:08

Message: 3 of 4

"Matt J" wrote in message <k18dj7$ocd$1@newscl01ah.mathworks.com>...
> "Giorgia " <emika@hotmail.it> wrote in message <k185tk$oj1$1@newscl01ah.mathworks.com>...
> > Hi everyone,
> > I have to process a signal that is composed of several smaller signals aligned togheter, it may occurs that two consecutive signals create at the border a cusp type discontinuity. Since I have to compute the FFT of the signal, how do you think the presence of a cusp might infect the final result? Do you eventually know if there is a way to predict and eventually correct the problem?
> ===========
>
> Nonsmooth signals tend to have wider spectra. To us bystanders, there's no obvious reason why this is a problem.

Beacuse eventually the cursp might infect the spectra in a range of frequency that are the ones I'm interested in looking at. I'm pretty sure the presence of a cuspid is going to influence the spectra (I've done some tests with simplier singals), I'm interested in detecting the cusp contribution in complex signal in order to remove it if possible.

Subject: fft, discontinuity

From: Matt J

Date: 24 Aug, 2012 18:34:07

Message: 4 of 4

"Giorgia " <emika@hotmail.it> wrote in message <k18eqk$t8f$1@newscl01ah.mathworks.com>...
>
I'm interested in detecting the cusp contribution in complex signal in order to remove it if possible.
================

Well, post an illustration of the cusp so that we know what it looks like. Also, post an example/description of what you'd like to replace it with.

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