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A Guide to the FFT-2nd Edition Plus

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09 Aug 2004 (Updated )

A guide to the use of the fft algorithm.

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Description

The fft of 3 functions are compared with their analytic transforms. The method proposal produce results that are super imposable with the theoretical predictions.
Odd and even number of points are considered.
(The algorithm works correctly in both cases).

Acknowledgements

This file inspired Why Use Fftshift(Fft(Fftshift(X))) In Matlab Instead Of Fft(X)?.

MATLAB release MATLAB 7.1.0 (R14SP3)
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Comments and Ratings (24)
01 Mar 2014 Dimitar

I get same results when using
X1=fftshift(fft(fftshift(x1)));
X2=fftshift(fft(fftshift(x2)));
X=X1+X2;
xo = ifftshift(ifft(ifftshift(X)))
OR
X1=(fft((x1)));
X2=(fft((x2)));
X=X1+X2;
xo = (ifft((X)))

My intervals are symmetric and power of 2.
Are these correct and is this normal in matlab 2013b?

08 May 2012 Michael Adelman

Thanks, very helpful.
Why do we need to use fftshift twice?

How about power measurement? What is the correct way plot the power of the signal after using this algorithm. I'm using modulated periodic signal.

28 Nov 2011 b3824855

Thank you very much! This is exactly what I was looking for.

02 Mar 2009 shan Kou

its very good - explains finally why we need fftshift twice. However, it should be stressed that the method works only for data of even size. For odd size data, the amplitude is correct but spectral phase will be wrong.

02 Mar 2009 shan Kou  
08 Aug 2008 Robert Kariniemi

Excellent description of the theory of the FFT.
But my code threw up errors...cannot define functions at this point?? Could not run it now. I will have to look into it a little.

05 Mar 2008 li taotao

Great,I like this file very much

18 Jun 2007 Fabrice Chane-Ming  
21 Mar 2007 M. Ashrith Kumar

its very good !! but slightly need for improvement

27 Feb 2007 B. Roossien

It's a good start, but the script contains the "clear all" and "close all" commands, which is a very bad habit to do.

03 Jan 2007 Andrey Worobey

Thanks so much man!!!

I have been looking for the solution for a year!

30 Dec 2006 Vishnuvenkatesh Dhage  
15 Dec 2006 Yani Jerome

I've found FourierTransform.m (ID 13327) very usefull too

24 Nov 2006 you you  
30 Oct 2006 ilaria eos  
21 Sep 2006 michel sebes  
31 Oct 2005 ISABEL CRISTINA GOMEZ

Gracias

15 Oct 2005 Wynn Ko Ko

Need to be improved.

29 Sep 2005 Gunasekaran Shanmgam

Gives nice overview of all FFT's

06 Aug 2005 samudrala jagadeesh

this is a good file for the users also beginers for filter designers thanks for the support

21 Jun 2005 srinu jella

u guys r impoptant for students like us. because we are in the initial stage of learning.we can learn from u .

19 Mar 2005 ding ding

very useful to a novice like me!
3q

14 Mar 2005 peng peng

helpful for student as me !

13 Aug 2004 Robert Chen

It's very useful to me.
Thank you very much!

Updates
13 Aug 2004

grammatical errors

05 Oct 2009

Odd and even number of points are considered.

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