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Acoustic-phonetic differences between normal and abnormal speech in reference to recognition systems for the aircraft cockpit are studied. The speech used in this research was collected in an anechoic chamber with an oxygen mask, and the speaker spoke (1) normally, (2) loudly ( approximately 10 dB above normal), and (3) with 90 dB of pink noise injected into the ears (invoking the Lombard reflex). Eighteen features were analyzed for approximately 11000 phonemes (from five speakers) to determine significant differences in the three types of speech. The most reliable trends observed were energy migrations in the frequency domain and the associated changes in spectral tilt for the sonorants.>
Stanton et al. (Mon,) studied this question.