On 09/30/10 13:15, Dave Phillips wrote: > Robin Gareus wrote: >> >> In layman terms: >> >> There's a smart French guy by the name of Joseph F. sitting inside it: >> If you play him some audio: He thinks: "Hey, this is actually just a few >> simple sine-waves added together (superpositioned)", he quickly >> calculates their frequencies and amplitudes and asks "Now, you want to >> change the duration?" easy: "I'll generate some new sine-waves with >> these frequencies and amplitudes, how long did you say you want?" >> >> (The smart thing about this French guy is that he actually speaks fluent >> English - Sorry I could not resist :) >> > > I recall a brief exchange on a DSP list that went something like this: > > 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?!) > I have read and understood some articles and descriptions of the FFT. > Mark Dolson's original article on the phase vocoder (in the Computer > Music Journal V10,#4, Winter 1986), is still a good introduction for > computer-based musicians, though it may be a bit too technical by > contemporary standards. > > Louigi, take a look at some descriptions of what an FFT does. It does > use "windows" but you'll have to do some homework to find out what's > meant by the term in this context. > > http://en.wikipedia.org/wiki/FFT > > Beware, that page is a maths page, it's not directly concerned with the > use of the FFT in music/sound applications. It may help to make some connection with the equations on http://en.wikipedia.org/wiki/Fourier_transform if you know that sin (x) = ImaginaryPartOf ( e^(i x) ) cos (x) = RealPartOf ( e^(i x) ) where i = sqrt(-1); > And btw, I agree wrt Paul's Extreme Stretch, it's a great tool. It is indeed. Kudos to Paul. FWIW, http://arss.sourceforge.net/ works similarly. It provides sound-to-image and image-to-sound functionality using FFT. You can also use it to do time-stretching but it's actually more fun to toy around with it: http://arss.sourceforge.net/examples.shtml > Best, > > dp > > _______________________________________________ > Linux-audio-dev mailing list > [email protected] > http://lists.linuxaudio.org/listinfo/linux-audio-dev _______________________________________________ Linux-audio-dev mailing list [email protected] http://lists.linuxaudio.org/listinfo/linux-audio-dev
