class:: SpecCentroid
summary:: Spectral centroid
categories:: UGens>FFT
related:: Classes/SpecFlatness, Classes/SpecPcile

description::
Given an link::Classes/FFT:: strong::chain::, this measures the emphasis::spectral:: centroid, which is the weighted mean frequency, or the "centre of mass" of the spectrum. (DC is ignored.)

This can be a useful indicator of the perceptual emphasis::brightness:: of a signal.

classmethods::
method:: kr

argument:: buffer
an link::Classes/FFT:: chain.

examples::

A link::Classes/Blip:: oscillator is ideal for demonstrating this because the number of harmonics is directly manipulated: as the number of harmonics increases, the centroid is pushed higher. In the example, left-to-right changes the number of harmonics, but up-to-down changes the fundamental pitch; note the different effects of these two on the centroid.

code::
s.boot;
b = Buffer.alloc(s,2048,1);
(
x = {
var in, chain, freq, rq, centroid;

//freq = LFPar.kr(0.3).exprange(100, 1000);
freq = MouseY.kr(1000, 100, 1);

in = Blip.ar(freq, MouseX.kr(1, 100, 1));

chain = FFT(b, in);

centroid = SpecCentroid.kr(chain);

Out.ar(0, in.dup * 0.1);
centroid.poll(10);
}.play(s);
)

x.free;
::