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105 Speech Intelligibility
STI-PA results screens
Models SE and DL
STI-PA modulation screen
In the Modulation measurement screen, the average decibel level over the run-
time in seven octave bands ranging from 125HZ to 8KHz with 14 frequencies is
displayed in a tabular format. These values are the signal to noise ratio
(accounts for any interfering background noise such as non-linear distortions,
electronics, reverberation, HVAC systems) in each attenuation band and
indicates which values are intelligible/unintelligible based on the CIS/STI scale.
NOTE: A high MTF value indicates that the listeners received the
message without any distortions or interference.
Figure 6-22: STI-PA Modulation screen
Table 6-4 defines the STI-PA: modulation frequencies for the seven octave
bands (per the IEC 60268-16 standard).
Table 6-5 defines the STI octave band with specific male and female weighting
factors used with STI-PA measurements (per the IEC 60268-16 standard).
Octave band Hz
125-250
500
1 k
2 k
4 k
8 k
First modulation
frequency Hz
1.00
.63
2.00
1.25
0.80
2.50
Second modulation
frequency Hz
5.00
3.15
10.0
6.25
4.00
12.5
Octave band Hz
125-250
500
1 k
2 k
4 k
8 k
Males
0.127
0.23
0
0.23
3
0.30
9
0.224
0.17
3
0.078
0.06
5
0.01
1
0.04
7
0.095
-
Females
0.117
0.22
3
0.21
6
0.32
8
0.250
0.19
4
0.099
0.06
6
0.06
2
0.02
5
0.076
-
LEQ
Average dB
level in band
Signal to noise ratio for each band
* Based on the CIS/STI scale ranging
from 0.00 – 1.00