1 Oct
2010
1 Oct
'10
12:28 a.m.
On Thursday 30 September 2010 23:16:32 fons(a)kokkinizita.net wrote:
On Thu, Sep 30, 2010 at 09:23:08PM +0200, Robin Gareus
wrote:
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
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.