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Subject: Re: fft amplitude relationship
Date: Tue, 6 Jan 2009 14:54:02 +0000 (UTC)
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"Darren " <dgoshi@ucla.edu> wrote in message <gju67h$avn$1@fred.mathworks.com>...
> Can someone point me to a technical reference/document that explains or discusses this fft (time/freq) amplitude scaling concept. Thanks,
> 
> Darren
> 
> 
> "Ken Garrard" <ken_garrardAT@ncsuDOT.edu> wrote in message <g1jvv5$pq4$1@fred.mathworks.com>...
> > "Bruce " <italianasa84@gmail.com> wrote in message 
> > <g1juri$c4v$1@fred.mathworks.com>...
> > > Thanks, what you mentioned was what I was looking for.
> > > - Bruce
> > 
> > Bruce,
> > 
> > Walter's answer is incomplete.  The DC and Nyquist values 
> > are unique and therefore do not have a 2 in the scale 
> > factor.
> > 
> > time(DC)      = frequency(DC) / N
> > time(Nyquist) = frequency(Nyquist) / N
> > time(all other points) = frequency(all other points) * 2 / N
> > 
> > Note that there is no Nyquist value for odd N.
> > 
> > Ken
> > 

If you can get hold of it, the book

Title The Fast Fourier Transform and its applications
Author E.O. Brigham

It will tell you all you ever want to know about FFT, written in an almost casual style. In my opinion - for what it is worth, this is the best document explaining FFT that I have come across in all of my long career in DSP.

I checked with Amazon, and it still appears to be available via some of the specialist book suppliers - but is expensive, so search your local library before purchasing it.

Regards

Dave Robinson