Excerpts from fons's message of 2010-09-30 14:29:01 +0200: > On Thu, Sep 30, 2010 at 01:53:44PM +0200, Robin Gareus wrote: > > > > Q: Can anyone explain the FFT in simple terms ? > > > A. No. > > > > LOL. > > > > basically, Fourier proved that any signal can be represented a sum of > > sine-waves. > > > > (well, that's not entirely true: it needs to be a periodic signal, but > > the period length can approach infinity...) > > > > FFT is "just" the implementation of that theorem (or Principle?!) > > The original Fourier Transform as invented by the smart French > guy of the same name does operate on continuous (as opposed to > sampled) data from -inf to +inf. The 'spectrum' interpretation > came later. It was originally a mathematical tool used to find > integrals of functions that would be impossible to integrate in > closed form, and Fourier himself used it to study the propagation > of heat in solids. > > The DFT (Discrete FT) is the same thing operating on sampled > signals. It is usually also limited in time. > > The FFT (Fast FT) is an algorithm to compute a finite-length > DFT very efficiently. > > The 'spectrum' interpretation is really quite ambiguous. > > You could take the DFT of e.g. a complete Beethoven symphony. > The result is the 'spectrum' and in theory this is fixed over > infinite time - the frequencies that are present according to > this spectrum are there *all the time*. But that is not how > we would perceive the music - we do not hear a constant mash > of all frequencies, the spectrum as we hear it changes over > time. > > Ciao, > > -- > FA > > There are three of them, and Alleline.
And I guess this is where the windowing comes in. Calculate the spectrum of small pieces instead. _______________________________________________ Linux-audio-dev mailing list [email protected] http://lists.linuxaudio.org/listinfo/linux-audio-dev
