Appendix E 189
Fitting Formula Tables
The conversions used by the FONIX 7000 Test System to convert
audiograms to target gain curves are the following:
NAL-RP FITTING FORMULA CALCULATION
The insertion gains at each frequency are calculated according to
the following formulas:
Freq (Hz) Insertion Gain (dB)
250 X + .31 HTL - 17dB + S
500 X + .31 HTL - 8dB + S
750 X + .31 HTL - 3dB + S
1000 X + .31 HTL + 1dB + S
1500 X + .31 HTL + 1dB + S
2000 X + .31 HTL - 1dB + S
3000 X + .31 HTL - 2dB + S
4000 X + .31 HTL - 2dB + S
6000 X + .31 HTL - 2dB + S
8000 X + .31 HTL - 2dB + S
Where you calculate X and S (Slope correction values) as follows:
a. T = (HTL @ 500Hz) + (HTL @ 1000Hz) + (HTL @ 2000Hz)
b. If T is less than or equal to 180dB, then
X = .05 x T
If T is greater than 180dB, then
X = (.05 x 180dB) + (.116 x ( T - 180dB)
c. If the HTL at 2000 Hz is less than 95dB, S = 0
If the HTL at 2000 Hz is greater than or equal to 95dB, then
apply the following slope correction factors at each frequency
based on the 2000Hz measurement:
2000Hz 250 500 750 1000 1500 2k 3k 4k 6k 8k
HTL (dB)
95 4 3 1 0 -1 -2 -2 -2 -2 -2
100 6 4 2 0 -2 -3 -3 -3 -3 -3
105 8 5 2 0 -3 -5 -5 -5 -5 -5
110 11 7 3 0 -3 -6 -6 -6 -6 -6
115 13 8 4 0 -4 -8 -8 -8 -8 -8
120 15 9 4 0 -5 -9 -9 -9 -9 -9
