# Audibility of tones in noise (ISO/TS 20065)

> 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/tonal-audibility-iso-20065.html

**Quantity:** Tonality · **Unit:** dB · **Also known as:** ISO/TS 20065, ISO/PAS 20065, tonal audibility, decisive audibility, ΔL_ta

Engineering method for the audibility of tones in noise, from critical-band analysis of narrow-band spectra. First published as ISO/PAS 20065:2016 and turned into ISO/TS 20065:2022, which notes that the method is not validated below 50 Hz.

The current edition is ISO/TS 20065:2022. No open-source implementation of it has been found. Implementations of earlier editions or related models: [phonometry](https://zhenxianli.github.io/LISQM/projects/phonometry.html) (Python; newly released, not yet seen to be widely used; ISO/PAS 20065:2016).

## Editions and who implements them

| Date | Edition | Status | What changed | Implemented by |
|---|---|---|---|---|
| 2022-12 | [ISO/TS 20065:2022](https://www.iso.org/standard/81518.html) | current | Technical specification; adds that the method is not validated below 50 Hz. | — |
| 2016-07 | [ISO/PAS 20065:2016](https://www.iso.org/standard/66941.html) | withdrawn | Publicly available specification; withdrawn in 2022. | [phonometry](https://zhenxianli.github.io/LISQM/projects/phonometry.html) |

## Implementations

| Project | Language | Edition | Functions | Validation (as stated) | Notes |
|---|---|---|---|---|---|
| [phonometry](https://zhenxianli.github.io/LISQM/projects/phonometry.html) | Python | [ISO/PAS 20065:2016](https://www.iso.org/standard/66941.html) (since 3.1.0) | `tone_audibility`, `analyze_spectrum`, `audibility_from_levels`, `mean_audibility`, `audibility_uncertainty` | standard or paper data; also compared with DIN 45681 Annex J reference program | Newly released project, not yet seen to be widely used. Follows the 2016 PAS, not the 2022 TS. Does not apply the A-weighting required by clause 5.3.2. DIN 45681 itself is not implemented. |

**See also:** [Tonal components and tone adjustment (DIN 45681)](https://zhenxianli.github.io/LISQM/metrics/tonality-din-45681.html), [Tonal audibility in environmental noise (ISO 1996-2)](https://zhenxianli.github.io/LISQM/metrics/tonal-audibility-iso-1996-2.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.

- [phonometry](https://zhenxianli.github.io/LISQM/projects/phonometry.html), ISO/PAS 20065:2016: standard or paper data; also compared with DIN 45681 Annex J reference program
  - Reproduces the Annex E worked example.
  - Parts are checked against DIN 45681:2005 and its Annex J reference program.

## References

1. ISO/PAS 20065:2016. Acoustics — Objective method for assessing the audibility of tones in noise — Engineering method. https://www.iso.org/standard/66941.html
2. ISO/TS 20065:2022. Acoustics — Objective method for assessing the audibility of tones in noise — Engineering method. https://www.iso.org/standard/81518.html