[PD] noise floor: median in audio signals, for peak extraction

Thomas Grill gr at grrrr.org
Sun Dec 25 21:09:39 CET 2011

```Hi Alexandre,
maybe the libsms integration into Pd is of use for you - it calculates
a model of sinusoidals + residual noise, the latter representing a
kind of "noise floor".
Those components can then also be modified and resynthesized.
http://mtg.upf.edu/static/libsms/

bests, gr~~~

2011/12/21 Alexandre Torres Porres <porres at gmail.com>:
> 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
> "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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--
Thomas Grill
http://grrrr.org

```