# zwickerloudness

> 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/projects/zwickerloudness-sourceforge.html

**Legacy project.** Not maintained. Its last commit was in June 2018, more than three years ago. Kept here for reference. Its code may follow an older edition and may not run with current software.

Console program in C, for BSD, Linux and Windows, that calculates the loudness of stationary sounds with Zwicker's method (ISO 532B / DIN 45631) from one-third-octave band levels. A companion tool analyses WAV files to produce those input files.

- **Full name:** Zwicker's Loudness Calculation SW + Tool (ISO 532B)
- **Repository:** https://sourceforge.net/projects/zwickerloudness/
- **Language:** C
- **Kind:** Application (A program to run, with a graphical or command-line interface; no programming needed.)
- **Group:** legacy (Archived, or no commit for three years or more. Kept for reference. The code may follow an older edition and may not run with current software.)
- **Licence:** GPL-2.0 — SourceForge lists "GNU General Public License version 2.0", but the license file in the release archive (loudness-020) has the author's own BSD-style terms, with a fourth clause: a significantly different project that reuses parts of the code must be open source as well and must reference the original code.
- **Latest release:** zwickerloudness-020 (2011-07)
- **Last commit:** 2018-06-05 (inactive since 2018-06)
- **Maintainers:** V. Portet
- **AI assistance:** not stated
- **How to cite:** The project does not say how to cite it. Cite the repository with the version or commit you used.
- **Entry checked:** 2026-10-08

## What it implements

| Metric | Edition | Functions | Status | Validation (as stated) | Notes |
|---|---|---|---|---|---|
| [Zwicker loudness](https://zhenxianli.github.io/LISQM/metrics/loudness-zwicker.html) | [DIN 45631:1991](https://www.dinmedia.de/en/standard/din-45631/1666531) (stationary, from one-third-octave band levels) | — | available | own tests only | Port of the 1991 BASIC program "according to DIN 45631 (ISO 532B)", the program that accompanies DIN 45631:1991; the same program is the basis of deeuu/loudness. |

## How it was validated

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

- [Zwicker loudness](https://zhenxianli.github.io/LISQM/metrics/loudness-zwicker.html), DIN 45631:1991: own tests only
  - Ported or adapted from BASIC program of DIN 45631 (Zwicker et al., 1991).
  - The documentation in the release archive says that tests with "classical cases", such as the included test WAV files, "seems to give correct results", and invites users to compare the output with that of the original BASIC program.

## Notes

- Partly ported from the BASIC "Program for calculating loudness according to DIN 45631 (ISO 532B)", published in the Journal of the Acoustical Society of Japan in 1991, as obtained from Osaka University's website.
- Distributed as release archives on SourceForge, from release 010 (2010-04-15) to zwickerloudness-020 (2011-07-01). The last-commit date given here (2018-06-05) is the project's "Last Update" date on SourceForge, not a commit date.

## Before you rely on it

- Stationary sounds only; there is no procedure for time-varying sounds.

## Sources

- https://sourceforge.net/projects/zwickerloudness/
- https://sourceforge.net/projects/zwickerloudness/files/
- https://sourceforge.net/projects/zwickerloudness/files/README.TXT/download
- https://sourceforge.net/projects/zwickerloudness/files/zwickerloudness-020/loudness-020.tar.gz/download