Metrics › Loudness

Loudness from the Sottek Hearing Model (ECMA-418-2)

Unit: sone_HMS · Also known as ECMA-418-2 loudness, Sottek Hearing Model, SHM loudness, sone_HMS, hearing model loudness

Loudness from the Sottek Hearing Model defined in ECMA-418-2. The hearing model (Clause 5) produces specific loudness; the 2nd edition (2022) added a loudness calculation for sounds with tonal and noise components (Clause 8). ECMA-418-2 has had four editions in five years, so implementations of different editions can disagree.

Editions and who implements them

Project map

The project map, with only the lines for Sottek Hearing Model loudness between the projects listed for it. Agreement between a project and the code it was ported or adapted from only checks the port.

• ported or adapted from another project
• the author's own code
• used at run time
• same contributor
• SQAT SQAT, MoSQITo, and sottek-hearing-model
• legacy legacy project

Scroll the picture sideways.

Implementations

Projects in bold and other established projects come first, then newly released, developing and legacy ones. Validation is what each project says about its own testing. The details are below, and the kinds of evidence are explained on the About page. The project map above shows which project was ported or adapted from which.

Also available through tools that call one of these implementations: rota-order (via sottek-hearing-model, ECMA-418-2:2025 (4th ed.)), pySQAT (via sottek-hearing-model, ECMA-418-2:2025 (4th ed.)), and PsychoBox (via MoSQITo, ECMA-418-2:2022 (2nd ed.)).

See also: Zwicker loudness (ISO 532-1, DIN 45631), Tonality from the Sottek Hearing Model (ECMA-418-2), Roughness from the Sottek Hearing Model (ECMA-418-2), Fluctuation strength from the Sottek Hearing Model (ECMA-418-2).

How they were validated

As reported by each project; LISQM has not run the code. Two implementations that agree can still share the same error. Kinds of evidence.

SQAT · ECMA-418-2:2025 (4th ed.)

compared with ArtemiS SUITE (HEAD acoustics)

Ported or adapted from refmap-psychoacoustics (the author's own code).

• Checked for the 4th edition against the ISO 226:2003 equal-loudness contours and against reference results from HEAD acoustics ArtemiS SUITE 17.1 (named in the source of SQAT's validation page) for a binaural recording of a train station (last checked in November 2025).

SQAT · ECMA-418-2:2024 (3rd ed.)

compared with ArtemiS SUITE (HEAD acoustics)

Ported or adapted from refmap-psychoacoustics (the author's own code).

• Checked against the ISO 226:2003 equal-loudness contours and against reference results from HEAD acoustics ArtemiS SUITE 15.7 (named in the source of SQAT's validation page) for a binaural recording of a train station.

MoSQITo · ECMA-418-2:2022 (2nd ed.)

standard or paper data (outcome not stated)

• Validation scripts compare with figures of the standard.

sottek-hearing-model · ECMA-418-2:2025 (4th ed.)

standard or paper data (calibration signals and one recording) also compared with ArtemiS SUITE (HEAD acoustics)

Ported or adapted from refmap-psychoacoustics (the author's own code).

• Unit tests check the standard's calibration signals (1 kHz, 40 dB gives 1 sone_HMS).
• RefMap's verification compared the Python code, before it became this package, and the MATLAB original with HEAD acoustics ArtemiS v17.1 for the two calibration signals and a 30 s binaural street recording.

Checked by the maintainer of LISQM: In personal use, Zhenxian LI found its results in very good agreement with those of HEAD acoustics ArtemiS SUITE. This is a personal check, not a published comparison.

refmap-psychoacoustics · ECMA-418-2:2025 (4th ed.)

compared with ArtemiS SUITE (HEAD acoustics)

• MATLAB and Python verified against HEAD acoustics ArtemiS v17.1 for a 1 kHz tone at 40 dB SPL, a 1 kHz tone amplitude-modulated at 70 Hz at 60 dB SPL and a 30 s binaural street recording.
• The audio and reference results are on Zenodo (doi:10.5281/zenodo.18849587).

MetaSona new · ECMA-418-2:2025 (4th ed.)

compared with SQAT (its source)

Ported or adapted from SQAT. It was compared with the code it was ported from, which checks the port only.

• The project says that detailed validation and reference comparisons are kept outside the repository; the results are not published.

phonometry new · ECMA-418-2:2025 (4th ed.)

standard or paper data (calibration signal only; outside the allowed adjustment)

• Checked at the calibration signal only, where it gives 0.9843 sone_HMS (−1.55 %).

rota-order new via sottek-hearing-model · ECMA-418-2:2025 (4th ed.)

own tests only

• Tests, which run only where sottek-hearing-model is installed (the project's continuous integration does not install it), check that the wrapper returns what a direct call of the package gives.

Mosqito.NET new · ECMA-418-2:2022 (2nd ed.)

compared with MoSQITo (its source)

Ported or adapted from MoSQITo. It was compared with the code it was ported from, which checks the port only.

• Every public function is compared with the output of Python MoSQITo for seven WAV files (three of them ISO 532-1 test signals), within 1 % (0.5 dB for levels); MoSQITo's unit tests are ported too.

pySQAT developing via sottek-hearing-model · ECMA-418-2:2025 (4th ed.)

compared with SQAT (also ported from refmap-psychoacoustics)

Code ported from the same source is expected to agree, so that comparison is not an independent check.

• Compared by validation/FINAL_VAL.py with the bundled SQAT v1.3 MATLAB code, which follows ECMA-418-2:2024 (3rd edition), so the comparison crosses editions.

MoSQITo-FDP legacy · ECMA-418-2:2020 (1st ed.)

standard or paper data

Ported or adapted from MoSQITo (the author's own code).

• Validation scripts compare the ear filter and model output with figures and values from ECMA-418-2 and ECMA-74 Annex F.

Not stated by PsychoBox.

Before you compare numbers

Implementations of the same metric can give different numbers without either being wrong. Check these choices first.

• Edition. The four editions give different results; compare implementations of the same edition (see the table of editions).
• Which loudness. Clause 5 gives the hearing model's basic loudness; from the 2nd edition on, Clause 8 defines the loudness to report. MoSQITo and Mosqito.NET compute only the Clause 5 value, while the RefMap code and its ports (SQAT, sottek-hearing-model, MetaSona) compute the Clause 8 loudness.
• Start of the signal. The filters need time to settle, so overall values leave out the first 304 ms (Section 8.1.4 of the 2025 edition, as cited by SQAT, which enforces it).
• Sample rate. The model is defined at 48 kHz; other rates are resampled, and resamplers differ slightly.
• Sound field and channels. The outer- and middle-ear filter can be free frontal or, from the 3rd edition, diffuse, and two channels can be combined into one binaural value. Check both settings.

What the projects state:

SQAT

• Statistics take the nearest rank of the sorted time series, without interpolation (get_exceeded_value), and leave out the first time_skip seconds; the code enforces at least 304 ms (it cites ECMA-418-2:2025, Section 8.1.4).

sottek-hearing-model

• Input at other sample rates is resampled to 48 kHz.

MetaSona new

• Expects calibrated sound pressure in pascals.
• The C functions require 48 kHz input; the Python interface resamples other rates to 48 kHz (SciPy resample_poly).
• time_skip_s (default 0 s) leaves out the start of the signal from the reported frames; the computation still runs over the whole signal. Time-varying results include every complete frame, labelled at frame centres, which differs from SQAT's handling of the last frame and of time stamps.

rota-order new

• For the ECMA-418-2 metrics, vs_rpm takes by default the mean of the loudness and the tonality in each speed bin, the tonality only above 0.02 tu_HMS, and the 90th percentile of the roughness, after about 0.3 s (0.6 s for SQAT's tonality).
• Input in any unit is turned into sound pressure in Pa by an explicit calibration factor and resampled to 48 kHz.

References

1. ECMA-418-2:2020 (1st ed.). Psychoacoustic metrics for ITT equipment — Part 2 (models based on human perception). https://ecma-international.org/wp-content/uploads/ECMA-418-2_1st_edition_december_2020.pdf
2. ECMA-418-2:2022 (2nd ed.). Psychoacoustic metrics for ITT equipment — Part 2 (models based on human perception). https://ecma-international.org/wp-content/uploads/ECMA-418-2_2nd_edition_december_2022.pdf
3. ECMA-418-2:2024 (3rd ed.). Psychoacoustic metrics for ITT equipment — Part 2 (methods for describing human perception based on the Sottek Hearing Model). https://ecma-international.org/wp-content/uploads/ECMA-418-2_3rd_edition_december_2024.pdf
4. ECMA-418-2:2025 (4th ed.). Psychoacoustic metrics for ITT equipment — Part 2 (methods for describing human perception based on the Sottek Hearing Model). https://ecma-international.org/wp-content/uploads/ECMA-418-2_4th_edition_june_2025.pdf