SpectralModerate signal
Spectral flatness
How noise-like versus tone-like a spectrum is, expressed as a single ratio.
Spectral flatness compares the geometric mean of a spectrum to its arithmetic mean. A pure sine wave has flatness near zero; white noise has flatness near one. Real music sits between the two and moves around as the arrangement changes.
It is useful in detection mostly as a texture descriptor for the upper bands. Synthesised high-frequency content can be either too smooth — a modelled hiss with no structure — or too structured, showing regular energy where a real cymbal would show chaos.
How this tool uses it
Computed on the upper spectrum and combined with high-band energy distribution; contributes at moderate weight and is discounted on low-bitrate files.
What else produces the same reading
- Noise reduction and de-noising plug-ins smooth the same bands.
- Vinyl rips and tape sources add broadband noise that raises flatness.
- Any codec below roughly 192 kbps rewrites this measurement entirely.