Fig. 2From: Exploiting temporal and nonstationary features in breathing sound analysis for multiple obstructive sleep apnea severity classificationRepresentative example of the time domain analysis of sleep sound. a A raw audio data example of the OSA severe group and b its quantized signal’s energy. c The 4 × 4 transition matrix including probability values, which is calculated by (b). d–f Example results of the OSA mild groupBack to article page