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Verifit User’s Guide Version 2.8
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18.10 SII calculation in Speechmap
FastFacts 18.10: SII calculation in Speechmap
The Verifit calculates a Speech Intelligibility Index (SII) value (in %) for unaided
speech at 70 dB SPL and for each aided test. The calculations use the 1/3 octave
band method of ANSI S3.5 –1997 without the 160 Hz band and without masking
effects with results expressed as a % by multiplying by 100. Level distortion
effects are included but no hearing loss desensitization is applied. An idealized
speech region of LTASS +/- 15 dB is used.
The speech recognition associated with a given SII is a function of the test
material and the cognitive abilities of the listener. There is considerable individual
variability in relating the SII to speech recognition, especially amongst impaired
listeners. The following shows expected nominal recognition scores vs SII for
normals on the Connected Speech Test (Sherbecoe and Studebaker 2003).
SII (%) Score (%)
10
1
15
8
20
20
25
45
30
60
35
74
40
84
45
90
50
94
55
96
60
98
70
99
80
100
90
100
