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

> Part of [LISQM](https://zhenxianli.github.io/LISQM/) (List of Implementations of Sound Quality Metrics), a list of open-source implementations of psychoacoustic metrics. Data as of 2026-10-28. Web page: https://zhenxianli.github.io/LISQM/metrics/loudness-ecma-418-2.html

**Quantity:** Loudness · **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.

The current edition is ECMA-418-2:2025 (4th ed.). Open-source implementations of it: **[SQAT](https://zhenxianli.github.io/LISQM/projects/sqat.html)** (MATLAB), **[sottek-hearing-model](https://zhenxianli.github.io/LISQM/projects/sottek-hearing-model.html)** (Python; mono or stereo, with combined binaural output), [refmap-psychoacoustics](https://zhenxianli.github.io/LISQM/projects/refmap-psychoacoustics.html) (MATLAB, Python; binaural and specific loudness), [MetaSona](https://zhenxianli.github.io/LISQM/projects/metasona.html) (C, Python; newly released, not yet seen to be widely used; Clause 8 loudness with tonal/noise separation; mono or stereo), and [phonometry](https://zhenxianli.github.io/LISQM/projects/phonometry.html) (Python; newly released, not yet seen to be widely used; mono only). Implementations of earlier editions or related models: **[SQAT](https://zhenxianli.github.io/LISQM/projects/sqat.html)** (MATLAB; ECMA-418-2:2024 (3rd ed.); mono or two channels with binaural combination), **[MoSQITo](https://zhenxianli.github.io/LISQM/projects/mosqito.html)** (Python; ECMA-418-2:2022 (2nd ed.); Clause 5 hearing-model specific and total loudness only; the Clause 8 loudness added in the 2nd edition is not implemented), [Mosqito.NET](https://zhenxianli.github.io/LISQM/projects/mosqito-net.html) (C#; newly released, not yet seen to be widely used; ECMA-418-2:2022 (2nd ed.); Clause 5 hearing-model loudness only, as in MoSQITo), and [MoSQITo-FDP](https://zhenxianli.github.io/LISQM/projects/mosqito-fdp.html) (Python; legacy, archived; ECMA-418-2:2020 (1st ed.); hearing model with specific and total loudness).

## Editions and who implements them

| Date | Edition | Status | What changed | Implemented by |
|---|---|---|---|---|
| 2025-06 | [ECMA-418-2:2025 (4th ed.)](https://ecma-international.org/wp-content/uploads/ECMA-418-2_4th_edition_june_2025.pdf) | current | Hearing-model clauses 5.1.2.2 and 5.1.5.2 revised; conformance requires 48 kHz sampling. | **[SQAT](https://zhenxianli.github.io/LISQM/projects/sqat.html)**, **[sottek-hearing-model](https://zhenxianli.github.io/LISQM/projects/sottek-hearing-model.html)**, [refmap-psychoacoustics](https://zhenxianli.github.io/LISQM/projects/refmap-psychoacoustics.html), [MetaSona](https://zhenxianli.github.io/LISQM/projects/metasona.html), [phonometry](https://zhenxianli.github.io/LISQM/projects/phonometry.html) |
| 2024-12 | [ECMA-418-2:2024 (3rd ed.)](https://ecma-international.org/wp-content/uploads/ECMA-418-2_3rd_edition_december_2024.pdf) | superseded | Adds a diffuse-field outer and middle ear filter. | **[SQAT](https://zhenxianli.github.io/LISQM/projects/sqat.html)** |
| 2022-12 | [ECMA-418-2:2022 (2nd ed.)](https://ecma-international.org/wp-content/uploads/ECMA-418-2_2nd_edition_december_2022.pdf) | superseded | New Clause 8, loudness of sounds with subcritical or wider bandwidth. | **[MoSQITo](https://zhenxianli.github.io/LISQM/projects/mosqito.html)**, [Mosqito.NET](https://zhenxianli.github.io/LISQM/projects/mosqito-net.html) |
| 2020-12 | [ECMA-418-2:2020 (1st ed.)](https://ecma-international.org/wp-content/uploads/ECMA-418-2_1st_edition_december_2020.pdf) | superseded | Hearing model (Clause 5) with specific loudness. | [MoSQITo-FDP](https://zhenxianli.github.io/LISQM/projects/mosqito-fdp.html) |

## Project map

The lines of the project map for Sottek Hearing Model loudness only, between the projects listed for it (the whole map: https://zhenxianli.github.io/LISQM/projects/map.md). Agreement between a project and the code it was ported or adapted from only checks the port.

### Ported or adapted from another project

- From **[SQAT](https://zhenxianli.github.io/LISQM/projects/sqat.html)**: [MetaSona](https://zhenxianli.github.io/LISQM/projects/metasona.html) (ECMA-418-2:2025 (4th ed.))
- From **[MoSQITo](https://zhenxianli.github.io/LISQM/projects/mosqito.html)**: [Mosqito.NET](https://zhenxianli.github.io/LISQM/projects/mosqito-net.html) (ECMA-418-2:2022 (2nd ed.))

### The author's own code

- From [refmap-psychoacoustics](https://zhenxianli.github.io/LISQM/projects/refmap-psychoacoustics.html) (Mike Lotinga): **[SQAT](https://zhenxianli.github.io/LISQM/projects/sqat.html)** (ECMA-418-2:2025 (4th ed.) and ECMA-418-2:2024 (3rd ed.)); **[sottek-hearing-model](https://zhenxianli.github.io/LISQM/projects/sottek-hearing-model.html)** (ECMA-418-2:2025 (4th ed.))
- From **[MoSQITo](https://zhenxianli.github.io/LISQM/projects/mosqito.html)** (Daniel Jiménez-Caminero Costa): [MoSQITo-FDP](https://zhenxianli.github.io/LISQM/projects/mosqito-fdp.html) (ECMA-418-2:2020 (1st ed.))

### Used at run time

- [rota-order](https://zhenxianli.github.io/LISQM/projects/rota-order.html) calls **[sottek-hearing-model](https://zhenxianli.github.io/LISQM/projects/sottek-hearing-model.html)** (ECMA-418-2:2025 (4th ed.))
- [pySQAT](https://zhenxianli.github.io/LISQM/projects/pysqat.html) calls **[sottek-hearing-model](https://zhenxianli.github.io/LISQM/projects/sottek-hearing-model.html)** (ECMA-418-2:2025 (4th ed.))
- [PsychoBox](https://zhenxianli.github.io/LISQM/projects/psychobox.html) calls **[MoSQITo](https://zhenxianli.github.io/LISQM/projects/mosqito.html)** (ECMA-418-2:2022 (2nd ed.))

### Same contributor

- **[SQAT](https://zhenxianli.github.io/LISQM/projects/sqat.html)** and **[sottek-hearing-model](https://zhenxianli.github.io/LISQM/projects/sottek-hearing-model.html)** (Mike Lotinga)

On the map without a line, as no relation to another project listed for Sottek Hearing Model loudness is recorded for them: [phonometry](https://zhenxianli.github.io/LISQM/projects/phonometry.html).

## Implementations

| Project | Language | Edition | Functions | Validation (as stated) | Notes |
|---|---|---|---|---|---|
| **[SQAT](https://zhenxianli.github.io/LISQM/projects/sqat.html)** | MATLAB | [ECMA-418-2:2025 (4th ed.)](https://ecma-international.org/wp-content/uploads/ECMA-418-2_4th_edition_june_2025.pdf) (since v2.0) | `Loudness_ECMA418_2`, `LoudnessFromComp_ECMA418_2` | compared with ArtemiS SUITE (HEAD acoustics) | Updated to the 4th edition in 2025. |
| **[SQAT](https://zhenxianli.github.io/LISQM/projects/sqat.html)** | MATLAB | [ECMA-418-2:2024 (3rd ed.)](https://ecma-international.org/wp-content/uploads/ECMA-418-2_3rd_edition_december_2024.pdf) (mono or two channels with binaural combination; since v1.3) | `Loudness_ECMA418_2`, `LoudnessFromComp_ECMA418_2` | compared with ArtemiS SUITE (HEAD acoustics) | In v1.3; v2.0 follows the 4th edition. |
| **[MoSQITo](https://zhenxianli.github.io/LISQM/projects/mosqito.html)** | Python | [ECMA-418-2:2022 (2nd ed.)](https://ecma-international.org/wp-content/uploads/ECMA-418-2_2nd_edition_december_2022.pdf) (Clause 5 hearing-model specific and total loudness only; the Clause 8 loudness added in the 2nd edition is not implemented; since 1.2.0) | `loudness_ecma` | standard or paper data (outcome not stated) | Followed the 1st edition (2020) in versions 1.0.0–1.1.1 and the 2nd edition (2022) from 1.2.0. It grew out of the hearing model that Daniel Jiménez-Caminero added in May 2021, which is also kept in MoSQITo-FDP. |
| **[sottek-hearing-model](https://zhenxianli.github.io/LISQM/projects/sottek-hearing-model.html)** | Python | [ECMA-418-2:2025 (4th ed.)](https://ecma-international.org/wp-content/uploads/ECMA-418-2_4th_edition_june_2025.pdf) (mono or stereo, with combined binaural output; since 0.1.9) | `shm_loudness_ecma`, `shm_loudness_ecma_from_comp` | standard or paper data (calibration signals and one recording); also compared with ArtemiS SUITE (HEAD acoustics) | — |
| [refmap-psychoacoustics](https://zhenxianli.github.io/LISQM/projects/refmap-psychoacoustics.html) | MATLAB, Python | [ECMA-418-2:2025 (4th ed.)](https://ecma-international.org/wp-content/uploads/ECMA-418-2_4th_edition_june_2025.pdf) (binaural and specific loudness) | `acousticSHMLoudness`, `acousticSHMLoudnessFromComponent` | compared with ArtemiS SUITE (HEAD acoustics) | — |
| [MetaSona](https://zhenxianli.github.io/LISQM/projects/metasona.html) | C, Python | [ECMA-418-2:2025 (4th ed.)](https://ecma-international.org/wp-content/uploads/ECMA-418-2_4th_edition_june_2025.pdf) (Clause 8 loudness with tonal/noise separation; mono or stereo; since 0.2.0) | `loudness_ecma`, `ecma_tonal_analysis` | compared with SQAT (its source) | Newly released project, not yet seen to be widely used. Adapted from the SQAT/RefMap MATLAB code by Lotinga and Torjussen. |
| [phonometry](https://zhenxianli.github.io/LISQM/projects/phonometry.html) | Python | [ECMA-418-2:2025 (4th ed.)](https://ecma-international.org/wp-content/uploads/ECMA-418-2_4th_edition_june_2025.pdf) (mono only; since 3.1.0) | `loudness_ecma` | standard or paper data (calibration signal only; outside the allowed adjustment) | Newly released project, not yet seen to be widely used. |
| [Mosqito.NET](https://zhenxianli.github.io/LISQM/projects/mosqito-net.html) | C# | [ECMA-418-2:2022 (2nd ed.)](https://ecma-international.org/wp-content/uploads/ECMA-418-2_2nd_edition_december_2022.pdf) (Clause 5 hearing-model loudness only, as in MoSQITo) | `Sq.LoudnessEcma` | compared with MoSQITo (its source) | Newly released project, not yet seen to be widely used. |
| [MoSQITo-FDP](https://zhenxianli.github.io/LISQM/projects/mosqito-fdp.html) | Python | [ECMA-418-2:2020 (1st ed.)](https://ecma-international.org/wp-content/uploads/ECMA-418-2_1st_edition_december_2020.pdf) (hearing model with specific and total loudness) | `comp_loudness` | standard or paper data | Legacy project, no longer maintained. Module `mosqito.functions.hearing_model`. Its author committed the same hearing model to MoSQITo on 2021-05-30, two weeks before this snapshot. |

Also available through tools that call one of these implementations: [rota-order](https://zhenxianli.github.io/LISQM/projects/rota-order.html) (via sottek-hearing-model, ECMA-418-2:2025 (4th ed.)), [pySQAT](https://zhenxianli.github.io/LISQM/projects/pysqat.html) (via sottek-hearing-model, ECMA-418-2:2025 (4th ed.)), and [PsychoBox](https://zhenxianli.github.io/LISQM/projects/psychobox.html) (via MoSQITo, ECMA-418-2:2022 (2nd ed.)).

**See also:** [Zwicker loudness (ISO 532-1, DIN 45631)](https://zhenxianli.github.io/LISQM/metrics/loudness-zwicker.html), [Tonality from the Sottek Hearing Model (ECMA-418-2)](https://zhenxianli.github.io/LISQM/metrics/tonality-ecma-418-2.html), [Roughness from the Sottek Hearing Model (ECMA-418-2)](https://zhenxianli.github.io/LISQM/metrics/roughness-ecma-418-2.html), [Fluctuation strength from the Sottek Hearing Model (ECMA-418-2)](https://zhenxianli.github.io/LISQM/metrics/fluctuation-strength-ecma-418-2.html)

## 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.

- **[SQAT](https://zhenxianli.github.io/LISQM/projects/sqat.html)**, ECMA-418-2:2025 (4th ed.): compared with ArtemiS SUITE (HEAD acoustics)
  - Ported or adapted from [refmap-psychoacoustics](https://zhenxianli.github.io/LISQM/projects/refmap-psychoacoustics.html) (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](https://zhenxianli.github.io/LISQM/projects/sqat.html)**, ECMA-418-2:2024 (3rd ed.): compared with ArtemiS SUITE (HEAD acoustics)
  - Ported or adapted from [refmap-psychoacoustics](https://zhenxianli.github.io/LISQM/projects/refmap-psychoacoustics.html) (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](https://zhenxianli.github.io/LISQM/projects/mosqito.html)**, ECMA-418-2:2022 (2nd ed.): standard or paper data (outcome not stated)
  - Validation scripts compare with figures of the standard.
- **[sottek-hearing-model](https://zhenxianli.github.io/LISQM/projects/sottek-hearing-model.html)**, 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](https://zhenxianli.github.io/LISQM/projects/refmap-psychoacoustics.html) (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](https://zhenxianli.github.io/LISQM/projects/refmap-psychoacoustics.html), 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](https://zhenxianli.github.io/LISQM/projects/metasona.html), ECMA-418-2:2025 (4th ed.): compared with **[SQAT](https://zhenxianli.github.io/LISQM/projects/sqat.html)** (its source)
  - Ported or adapted from **[SQAT](https://zhenxianli.github.io/LISQM/projects/sqat.html)**. 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](https://zhenxianli.github.io/LISQM/projects/phonometry.html), 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](https://zhenxianli.github.io/LISQM/projects/rota-order.html) (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](https://zhenxianli.github.io/LISQM/projects/mosqito-net.html), ECMA-418-2:2022 (2nd ed.): compared with **[MoSQITo](https://zhenxianli.github.io/LISQM/projects/mosqito.html)** (its source)
  - Ported or adapted from **[MoSQITo](https://zhenxianli.github.io/LISQM/projects/mosqito.html)**. 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](https://zhenxianli.github.io/LISQM/projects/pysqat.html) (via sottek-hearing-model), ECMA-418-2:2025 (4th ed.): compared with **[SQAT](https://zhenxianli.github.io/LISQM/projects/sqat.html)** (also ported from [refmap-psychoacoustics](https://zhenxianli.github.io/LISQM/projects/refmap-psychoacoustics.html))
  - 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](https://zhenxianli.github.io/LISQM/projects/mosqito-fdp.html), ECMA-418-2:2020 (1st ed.): standard or paper data
  - Ported or adapted from **[MoSQITo](https://zhenxianli.github.io/LISQM/projects/mosqito.html)** (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](https://zhenxianli.github.io/LISQM/projects/sqat.html)**: 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](https://zhenxianli.github.io/LISQM/projects/sottek-hearing-model.html)**: Input at other sample rates is resampled to 48 kHz.
- [MetaSona](https://zhenxianli.github.io/LISQM/projects/metasona.html): 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](https://zhenxianli.github.io/LISQM/projects/rota-order.html): 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