A futher simplfication of the Ao method was created by assuming that the dynamic range of speech encompasses 25 dB. The speech spectrum was again plotted on the dB HL scale with a dynamic range from 20-45 dB HL at 500, 1000, 2000, and 4000 Hz and each band was given an equal importance weighting for speech.
The audiogram on the left shows the speech spectrum with m representing the minimum intensity level of speech and p representing the maximum intensity level of conversational speech. (adapted from Pavlovic, 1991).

Using this speech spectrum, Pavlovic (1991) computed the AI using his proposed As (s for simple) method. First, the number of dB that are audible at 500, 1000, 2000, & 4000 Hz are added (grey area). This number is then divided by 100 (total dB available) to give the AI. The number of "audible decibles" in the example to the right are 25, 15, 15, and 0, for a total of 55. 55/100 gives an AI of .55 for this hearing loss. An aided AI is computed by adding the insertion gain to the minima and maxima for the speech spectrum at 500, 1000, 2000, and 4000 Hz and recalculating the AI. While the method is the least accurate of all of those proposed, it can be used for a "quick and dirty" method of estimating the AI.

Pavlovic (1991) also proposed a count-the-dot method for computing the AI. It was composed of 100 dots arranged to reflect the importance weighting for conversational speech as opposed to the weighting for nonsense syllables as was used in the Muller & Killion (1990) method. According to Pavlovic (1987), the weighting for "average speech" would be more appropriate to use the AI in evaluating hearing aids. The Ad (d for dot) method, as termed by Pavlovic (1991), is calculated by counting the number of dots which are audible to a patient. If a patient's threshold line intersects a dot, and more than half of it is below the line, it should be included in the count. (Ad audiogram adapted from Pavlovic, 1991).
There are two methods used in the Audiologist's Toolbox to compute the AI. One is a method developed by Pavlovic (1991), and one by ANSI (1986). They differ slightly in the number of frequency bands required and the speech spectrum used. Because of this, differences in the calculated AI for a given hearing loss may occur. The reader is referred to the original articles cited below for more information on these methods.

Articulation Index Main Page

Works Cited

American National Standards Institute. ANSI S3.5-1969 R 1986. American national standard methods for the calculation of the articulation index. New York:ANSI.

Mueller, H.G., Killion, M.C. (1990). An Easy Method For Calculating the Articulation Index Hearing Journal. 9:14-17.

Pavlovic, C.V. (1987) Derivation of primary parameters and procedeures for use in speech intelligibility predictions. Journal of the Acoustical Society of America 82:413-422.

Pavlovic, C.V. (1988) Articulation index predictions of speech intelligibility in hearing aid selection. Asha 8:63-65.