Spectral flatness

Spectral flatness or tonality coefficient,[1][2] also known as Wiener entropy,[3][4] is a measure used in digital signal processing to characterize an audio spectrum.

Spectral flatness is typically measured in decibels, and provides a way to quantify how much a sound resembles a pure tone, as opposed to being noise-like.

A high spectral flatness (approaching 1.0 for white noise) indicates that the spectrum has a similar amount of power in all spectral bands — this would sound similar to white noise, and the graph of the spectrum would appear relatively flat and smooth.

A low spectral flatness (approaching 0.0 for a pure tone) indicates that the spectral power is concentrated in a relatively small number of bands — this would typically sound like a mixture of sine waves, and the spectrum would appear "spiky".

[6] Spectral flatness has also been used in the analysis of electroencephalography (EEG) diagnostics and research,[7] and psychoacoustics in humans.