94 FONIX FP40 Portable Hearing Aid Analyzer
Figure 5.4.4—SPL screen displayed on an external monitor
5.5 Audibility Index (AI)
The Audibility Index screen displays the audiogram, target, and aided response in dB HL on one
display. Technically speaking, these aided responses should be called “aided audiograms” because
they incorporate the insertion gain obtained by making unaided and aided measurements. This
insertion gain is then added to the unaided audiogram to obtain the curves shown on the HL dis
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play.
The Audibility Index shows you what percentage of speech sounds are audible to the client with the
aided audiograms you have obtained. This Audibility Index is based on the Hearing Level at eight
frequencies, weighed according to their importance. This index was primarily based on the publica
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tion by Mueller and Killion, “An Easy Method For Calculating the Articulation Index.” The Hearing
Journal, September 1990. The name Audibility Index came from “A is for Audibility” by Killion,
Mueller, Pavlovic, and Humes, The Hearing Journal, April 1993.
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