Human Factors Evaluation of Vocoders for Air Traffic Control ... - FAA

ANOVA testing for interaction of sex with background noise revealed that for both conditions of
the speaker, the effect of background noise was significant. Post hoc Tukey tests determined
which means differed. Table 28 depicts the results of the Tukey HSD tests for the interaction of
sex of speaker and background noise. Cases with jet background noise appear to score low in
this objective measure of intelligibility. This result is in agreement with the subjective ratings of
intelligibility previously presented. Figure 18 shows a graphical representation of these means.
Table 28. Tukey HSD Post Hoc Background Noise Comparisons for Message Completion Test
Scores
Sex of Speaker Result Interpretation
Male HPNJ Helicopter, propeller, and no background noise means are the same. No
background and jet means are the same. Jet background mean is lower
and different than helicopter and propeller means.
Female PNHJ Propeller background and no background means are the same. No
background and helicopter background means are the same. Helicopter
mean is lower and different than propeller mean. Jet background mean
is lower and different than all other means.
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Mean Intelligibility Score
8.95
8.9
8.85
8.8
8.75
8.7
JET PROP HELO NONE
Background Noise Condition
MALE
FEMALE
Figure 18. Mean scores from the Message Completion Test as a function of sex of speaker and
background noise.
3.3 Audio Preference Test
The data from this test were analyzed by counting the number of participants who preferred
vocoder model A and vocoder model B for each test condition. Individual chi-squared analysis
determined the effects of each experimental condition on vocoder preference.
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