Metrics
Each metric with its unit, the edition that an up-to-date implementation should follow, and the open-source projects that implement that edition. Every metric has its own page with all editions, function names and validation.
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Loudness
How loud a sound is perceived, in sone (loudness) and phon (loudness level). Four models are standardised: Zwicker (ISO 532-1), Moore–Glasberg (ISO 532-2), Moore–Glasberg–Schlittenlacher (ISO 532-3) and the Sottek Hearing Model (ECMA-418-2).
| Metric | Current edition | Implementations of it |
|---|---|---|
| Zwicker loudness sone, phon | ISO 532-1:2017 | mSQAT pyMoSQITo mAARAE cMetaSona new rsiso532-1-rs new rsKirin Hypha new c#Mosqito.NET new pyphonometry new c++SoundPalette new jlZwickerLoudness.jl new pypySQAT developing pyPsychoacousticParametersMeasurer legacy |
| Moore–Glasberg loudness sone, phon | ISO 532-2:2017 | pyphonometry new |
| Time-varying loudness (Moore–Glasberg–Schlittenlacher) sone, phon | ISO 532-3:2023 | miso532-3 (tv2018.m) pyphonometry new |
| Sottek Hearing Model loudness sone_HMS | ECMA-418-2:2025 (4th ed.) | mSQAT pysottek-hearing-model mrefmap-psychoacoustics cMetaSona new pyphonometry new |
Sharpness
The sensation produced by high-frequency content, in acum. Standardised in DIN 45692 on top of Zwicker loudness; ECMA-418-2 does not define sharpness.
| Metric | Current edition | Implementations of it |
|---|---|---|
| Sharpness acum | DIN 45692:2009 | mSQAT pyMoSQITo mrefmap-psychoacoustics cMetaSona new rsKirin Hypha new c#Mosqito.NET new pyphonometry new jlPsychoacousticMetrics.jl new c++SoundPalette new pypySQAT developing pyPsychoacousticParametersMeasurer legacy |
Roughness
The sensation produced by fast amplitude or frequency modulation (roughly 15 to 300 Hz, strongest near 70 Hz), in asper.
| Metric | Current edition | Implementations of it |
|---|---|---|
| Roughness (Daniel & Weber) asper | Daniel & Weber (1997) | mSQAT pyMoSQITo mAARAE mITA-Toolbox cMetaSona new c#Mosqito.NET new jlPsychoacousticMetrics.jl new c++SoundPalette new pypySQAT developing mPsySound3 legacy |
| Sottek Hearing Model roughness asper_HMS | ECMA-418-2:2025 (4th ed.) | mSQAT pysottek-hearing-model mrefmap-psychoacoustics cMetaSona new pyecma418-torch new pyphonometry new |
| Roughness (DIN 38455) asper | DIN 38455:2024 | none found |
Fluctuation strength
The sensation produced by slow modulation (below about 20 Hz, strongest near 4 Hz), in vacil.
| Metric | Current edition | Implementations of it |
|---|---|---|
| Fluctuation strength (Osses et al.) vacil | Osses et al. (2016) | mSQAT pyphonometry new jlPsychoacousticMetrics.jl new pypySQAT developing mfluctuation-strength-TUe legacy |
| Sottek Hearing Model fluctuation strength vacil_HMS | ECMA-418-2:2025 (4th ed.) | mSQAT PR pysottek-hearing-model unreleased pyecma418-torch new pyphonometry new |
Tonality
How prominent tonal components are. Covers psychoacoustic tonality models (Aures, ECMA-418-2) and the engineering measures used for product noise (tone-to-noise ratio, prominence ratio) and for environmental noise (tonal audibility and tone adjustments).
| Metric | Current edition | Implementations of it |
|---|---|---|
| Tonality (Aures) t.u. | Aures (1985b) | mSQAT pyMoSQITo PR cMetaSona new pypySQAT developing |
| Sottek Hearing Model tonality tu_HMS | ECMA-418-2:2025 (4th ed.) | mSQAT pysottek-hearing-model mrefmap-psychoacoustics cMetaSona new pyphonometry new |
| Tone-to-noise ratio and prominence ratio dB | ECMA-418-1:2024 (3rd ed.) | pyphonometry new pyrota-order new |
| Tonal components (DIN 45681) dB | DIN 45681:2005 | none found |
| Audibility of tones in noise (ISO/TS 20065) dB | ISO/TS 20065:2022 | none found |
| Tonal audibility (ISO 1996-2) dB | ISO 1996-2:2017 | pyMoSQITo PR pyphonometry new |
| Tonal audibility of wind turbines (IEC 61400-11) dB | IEC 61400-11:2012+AMD1:2018 | pyphonometry new |
Impulsiveness
How prominent impulsive sounds are, and the adjustment applied to them in environmental noise assessment.
| Metric | Current edition | Implementations of it |
|---|---|---|
| Impulse prominence dB | ISO/PAS 1996-3:2022 | pyphonometry new |
Psychoacoustic annoyance
Single-number models that combine loudness, sharpness, roughness, fluctuation strength and, in later models, tonality into a predicted annoyance.
| Metric | Current edition | Implementations of it |
|---|---|---|
| Psychoacoustic annoyance dimensionless | Widmann (1992), Zwicker & Fastl (1999), More (2010), and Di et al. (2016) | mSQAT mrefmap-psychoacoustics pyphonometry new jlPsychoacousticMetrics.jl new pypySQAT developing pyPsychoacousticParametersMeasurer legacy |
Related quantities
Quantities that psychoacoustic tools often include and that are closely tied to the metrics above.
| Metric | Current edition | Implementations of it |
|---|---|---|
| Equal-loudness contours dB SPL, phon | ISO 226:2023 | pyphonometry new |
| Perceived noise level and EPNL PNdB, EPNdB | ICAO Annex 16, Vol. I and 14 CFR Part 36 | mSQAT pyphonometry new pypySQAT developing pySUAVE legacy |
| Aural detectability d′ (detectability index), dB | Fidell et al. (1974) | mrefmap-psychoacoustics |