Audibility Index
Also written as: AI — Audibility Index
A metric expressing the proportion of the long-term average speech spectrum that is audible to a listener at a given listening level, typically as a percentage.
Full Definition
The audibility index (AI), also known as the speech intelligibility index (SII) in its more recent standardised form, quantifies the proportion of the speech signal that exceeds a listener's hearing threshold across the frequencies important for speech understanding. It is expressed as a value from 0 to 1 (or 0% to 100%), where 1.0 indicates that the entire speech spectrum is audible. The AI/SII is used in hearing aid verification to assess how much of the speech banana a fitted device makes audible. Editors must be aware that 'audibility index' is an older term and that 'speech intelligibility index' (ANSI S3.5) is the current formal designation; both remain in use across literature.
Usage
Usage note: 'Audibility index' is the legacy term; prefer 'speech intelligibility index' (SII) in documents aligned with ANSI S3.5. Note that 'articulation index' is an even older predecessor term—do not use unless quoting historical literature.
In Context
- "The fitting software displayed an audibility index of 0.72, indicating that nearly three-quarters of the speech spectrum was audible with the prescribed gain." — Hearing aid verification report
- "Authors should clarify whether they are using the older 'audibility index' or the ANSI-standardised 'speech intelligibility index' to ensure replicability." — Manuscript review comment