Figure 4.

Distributions of classifier probability outputs for DUS segments of test set for each of the four classes (n.u. stands for normalized units). The threshold of belonging to the Good class was fixed at 0.56 for the classifier. The majority of the distribution of the Good and Mostly Clean classes lies above this threshold, whereas the majority of Poor and Mostly Noise classes lies below this threshold, as was expected. The probability distributions were smoothed using a normal kernel function (Bowman and Azzalini, 1997).