additive

[Kimmo Koli]

On Wed, 12 Aug 1998 cyborg0 at GlobalEyes.net wrote:

> Jim Johnson wrote:
> > 
> > >theoretcly any acostic sound can be made in a modular
> > >ether by addtive or FM but this is hard to be made.
> > 
> > No, it's not theoretically possible to do that.
> 
> 
> well, thats not what they are teaching in engineering school these days!
> They say that (loosely quoted from textbook) "Any sound can be broken up
> into its harmonic series using fourier analysis. Once these basic
> frequencies and amplitudes are known, then, all that needs to be done to
> replicate the original sound is to do a time domain analysis of the
> amplitude changes of each of the various harmonics." 
> 
Well, that actually means that if you have for example a 1 second long
sample you can do a HUGE FFT from the from the whole sample to get the
spectral components from 0Hs, 1Hz, 2Hz etc. Then you can do a huge IFFT
which results in a continuous sound with a period of 1 second. So the FFT
know nothing of the harmonic or inharmonic content of the sample. Also this
means that a FFT has poor frequency resolution if the window is short.
That's why some people try to find different transforms that have
reasonable resolution both in time and frequency simultaneusly, would be
good in speech analysis/synthesis.  
 
So when they teach in engineering school theory they really mean theory,
not practice :-)

Best regards, 
-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-
   Kimmo Koli                         Helsinki University of Technology 
   kimmo at ecdl.hut.fi                  Electronic Circuit Design Laboratory
   http://www.ecdl.hut.fi/~kimmo      P.O.Box 3000
   Tel:  +358 9 451 2273              FIN-02015 HUT
   Fax:  +358 9 451 2269              Finland 
=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=