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Some characteristics of speech produced under high G-force and pressure breathing

The performance of speech recognisers in a combat aircraft is degraded seriously by the extreme physical stresses to which the crew are subjected. This paper describes measurements of first and second formant frequencies of nine vowels from one speaker recorded under high levels of acceleration, with and without positive pressure breathing. Under acceleration alone, F2 is reduced for high front vowels, while F1 remains constant, but for back and mid vowels, F1 reduces with little change in F2. When positive pressure breathing is introduced, nearly all vowels are affected, and the "vowel triangle" on the F1-F2 plane collapses inwards, towards the neutral vowel position. If these changes are found to be consistent between speakers, it is hoped to develop techniques of voice transformation to reverse them and thus improve the performance of speech recognisers in this harsh environment.