Articulation Index

Articulation Index (AI) is a quantitative measure used in audiology and acoustics to predict the proportion of normal conversational speech that is audible to a person with a particular hearing impairment. The AI is a number between 0 and 1, where 1 indicates that all speech sounds are audible and 0 indicates that no speech sounds are audible.

Overview

The Articulation Index was developed in the mid-20th century by researchers at Bell Labs who were interested in the effects of noise and hearing loss on telephone communication. The AI is calculated based on the frequency and intensity of speech sounds, the individual's hearing thresholds at different frequencies, and the background noise level.

Calculation

The calculation of the AI involves several steps. First, the speech signal is divided into frequency bands, and the average intensity in each band is calculated. Next, the individual's hearing thresholds in each band are determined. The difference between the speech intensity and the hearing threshold in each band is the signal-to-noise ratio (SNR). The SNR in each band is then weighted according to the band's importance for speech understanding, and the weighted SNRs are summed to give the AI.

Applications

The AI is used in several areas of audiology and acoustics. It is used to predict the benefit of hearing aids and cochlear implants, to design public address systems, and to assess the impact of environmental noise on speech communication. It is also used in research to study the effects of hearing loss and noise on speech understanding.

See also

• Speech intelligibility
• Audiogram
• Signal-to-noise ratio
• Hearing aid
• Cochlear implant