EAQUAL (Evaluation of Audio Quality) is an open source ITU-R BS.1387 implementation developed by the DSP engineer Alexander Lerch - the creator of the Compaact! AAC encoder.

The ITU-R BS.1387 standard aims to provide objective quality measurement for compressed audio signals. Unlike subjective audio comparisons (listening tests) that depend on each listener's auditory system, EAQUAL mathematically models the same auditory system, therefore generating consistent results across a broad spectrum of samples. As the author once described, in the context of listening tests: "Perhaps you should think of EAQUAL as _one_ listener whose results are not depending on his mood and his concentration, who never gets tired and whose results are repeatable."

The most relevant output of EAQUAL is the ODG (Objective Difference Grade), a numeric value. An ODG of -4 means a very annoying disturbance, while an ODG of 0 means there is no perceptible difference (according to the mathematical model) between the samples being evaluated. Wim Speekenbrink tested several samples on several encoders (of that time, early 2002) and published the EAQUAL results at his web site.

Alexander stopped developing EAQUAL on February 2002 because of threats from the patent owners, therefore version 0.1.3a, below, is the last release.

Big thanks to Martin Wagner for reminding me of EAQUAL.


Date: 2002-02-06
Version: 0.1.3 alpha
Interface: Command line
Platform: Win32
Download: eaqual013.zip - 212kB
Sources: eaqual013.tar.gz - 384kB