[LAD] Listing lowest and highest frequencies in a track?
fons at linuxaudio.org
Fri Aug 31 20:11:23 UTC 2012
On Fri, Aug 31, 2012 at 09:47:56PM +0300, Sakari Bergen wrote:
> However, the biggest problem in the question is that it doesn't consider
> the time-frequency uncertainty, and the fundamental nature of time limited
> signals (a time limited signal can't be band limited).
> You can not measure frequencies whose period is shorter than the
> measurement data. That means that you can't measure the power at 1Hz with a
> resolution better than one second. This means that the "where they are"
> part of the question is not well defined.
While this is 100% correct, in practice 'the soup isn't eaten as hot
as it is served' (Flemish proverb, probably has equivalents in other
If you analyse say 200 ms of a signal then your resolution in the
frequency domain is indeed limited to something like 5 Hz. So a low
frequency signal such as a bass note will have its spectrum 'smeared
out', but assuming there's no other signal near in frequency, the peak
of the smeared out spectrum will be in the right place, and you can
still discover the musical pitch.
Human hearing easily violates the 'uncertainty principle', and it
can do this by making assumptions about the signal (such as the
one made above). If a 50 Hz bass note is a quarter tone (1.5 Hz)
out of tune, we can easily hear this even if the bass plays more
than 1.5 notes per second.
A world of exhaustive, reliable metadata would be an utopia.
It's also a pipe-dream, founded on self-delusion, nerd hubris
and hysterically inflated market opportunities. (Cory Doctorow)
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