Time- and spectrum-related variabilities in stressed speech under laboratory and real conditions

Stress induced by various types of situation leads to vocal signal modifications. Previous studies have indicated that stressed speech is associated with a higher fundamental frequency and noticeable changes in vowel spectrum. This paper presents pitch- and spectral-based analyses of stressed speech corpora drawn from both artificial and real situations. The laboratory corpus is obtained by means of the Stroop test, the real-case corpus is extracted from the Cockpit Voice Recording of a crashed aeroplane. Analyses relative to pitch are presented and an index of microprosodic variation, μ, is introduced. Spectrum-related indicators of stress are issued from a cumulative histogram of sound level and from statistical analyses of formant frequencies. Distances to the F1-F2-F3 centre are also investigated. All these variations, throughout the two different situations, show the direct link between some new vocal parameters and stress appearances. The results confirm the validity of laboratory experiments on stress, but emphazise quantitative as well as qualitative differences between the situations and the speakers involved.