On Thursday 30 September 2010 23:16:32 f...@kokkinizita.net wrote: > On Thu, Sep 30, 2010 at 09:23:08PM +0200, Robin Gareus wrote: > > Back when I was introduced to FT in some Physics lecture I was happy > > that I was able to use it and completely forgot to check the history :) > > Probably related to why I favored experimental Physics over Theory. > > If you're still living in Paris, make sure to visit the 'Musée des > Arts et Métiers' one day. Quite a nice place for vintage experimental > physics. It's also the place where the final mad scene of Umberto Eco's > novel "Foucault's Pendulum" is situated. The pendulum itself used to be > there, but it's now at the Panthéon. > > > > And I guess this is where the windowing comes in. Calculate the > > > spectrum of small pieces instead. > > > > correct. > > > > Furthermore there are different kind of windows (here a window refers to > > a block of audio-samples) and windows can overlap. That's where it gets > > complicated. > > Even windows won't save you from apparent madness. Imagine a signal > consisting of all zero samples, except one every second which has > value 1. Such a signal contains all frequencies that are a multiple > of 1 Hz, up to half the sample frequency. Those frequencies are present > all the time. Now take a window of say half a second. If it includes a > pulse you get more or less the same spectrum again. If it doesn't, you > get nothing... even if the frequencies should be there :-)
And if I remember correctly, the minimum frequency you get is double your window-width. So when you do smaller windows like a jack-buffer of 128 samples at 48kHz, you only get down to 187.5 Hz... You can however overcome this if you run a second much bigger window where you only extract the low frequencies. (Unless Fons corrects me on that...) Have fun, Arnold
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