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0611 RM500SL User’s Guide Version 2.8 Page 76
17.10 SII calculation in Speechmap
FastFacts 17.10: SII calculation in Speechmap
The RM500SL 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. 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