[PD] noise floor: median in audio signals, for peak extraction
Alexandre Torres Porres
porres at gmail.com
Wed Dec 21 00:29:43 CET 2011
Hi there, this is a technique for calculating the noise floor of a
spectrum, and extracting the peaks.
It'd be used pretty much like I04.Noie Gate Miller's example, that has the
"mask" table with a constant multiplier. We'd have instead this
"noise-floor" block of audio, also multiplied by a constant.
To get the noise floor, we take the magnitude (or power) spectrum and get
the median of small bits of it, like every 32 samples. So the values of
every 32 samples would be the median of that section...
this is where I got this from, check page 4 and 5
http://homepages.cae.wisc.edu/~sethares/software/SpectralTools.pdf
this would be kinda like using the [median] or [median_n] objects, but over
audio blocks and not number lists.
Since there's the need of calculating this in and using the result back in
the same block round into the audio chain, I can't put the spectrum into a
table, and then calculate the median over bits of it.
But then, how to do it? Should I be able to pull this out only if I write a
"median~" or [noise_floor~] external?
Or somehow there's another way to do this with some existing external, or a
similar technique, or even some audio math trick using [fexpr~] or
something?
This has to do with the other post I did about a project that attempts to
isolate notes into a chord in a spectrum, something like melodyne is does.
thanks
Alex
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