Analysis of the effects of physical task stress on the speech signal.

Physical task stress is known to affect the fundamental frequency and other measurements of the speech signal. A corpus of physical task stress speech is analyzed using a spectrum F-ratio and frame score distribution divergences. The measurements differ between phone classes, and are greater for vowels and nasals than for plosives and fricatives. In further analysis, frame score distribution divergences are used to measure the spectral dissimilarity between neutral and physical task stress speech. Frame scores are the log likelihood ratios between Gaussian mixture models (GMMs) of physical task stress and of neutral speech. Mel-frequency cepstral coefficients are used as the acoustic feature inputs to the GMMs. A Laplacian distribution is fitted to the frame scores for each of ten phone classes, and the symmetric Kullback-Leibler divergence is employed to measure the change in distribution from neutral to physical task stress. The results suggest that the spectral dissimilarity is greatest for the second level of a four level exertion measurement, and that spectral dissimilarity is greater for nasal phones than for plosives and fricatives. Further, the results suggest that different phone classes are affected differently by physical task stress.