Spectral centroid
The centre of mass of a sound's frequency spectrum — a numerical measure of brightness.
Spectral centroid is the amplitude-weighted average frequency present in a short window of audio. A track with lots of cymbal and sibilance has a high centroid; a bass-heavy dub mix has a low one. On its own the absolute value says almost nothing useful about origin, because it mostly describes genre and arrangement.
What is informative is how the centroid moves. In a performed recording it jitters constantly: a snare hit pushes it up for 40 milliseconds, a sustained pad pulls it down, a consonant spikes it. The variance of that movement over time is a rough proxy for how much genuine acoustic event variety a recording contains.
Generated and heavily processed audio often shows lower centroid variance across a track than a comparable live performance. It is a difference of degree, not of kind, which is exactly why it belongs in a weighted ensemble rather than in a rule.
How this tool uses it
Measured per analysis window; the variance across windows contributes to the spectral component of the score at moderate weight.
What else produces the same reading
- Multiband compression and limiting flatten brightness movement in human recordings.
- Programmed electronic music has genuinely low event variety.
- Lossy encoding removes high-band content and shifts the centroid downwards.