The Effects of High Altitude on Speech and Hearing

Speech energy in twelve contiguous frequency bands, each 250 mels wide, has been measured at simulated altitudes ranging from sea level to 40,000 feet in intervals of 5000 feet. Measurement of speech energy at 35,000 feet was also made with the subject talking into the open air of the altitude chamber. In any frequency band, the energy decrement of vowels and semi‐vowels, expressed in decibels, varies uniformly with altitude; however, there is little or no change in the energy of unvoiced consonants with altitude. The number of words per breath which a subject can say while maintaining constant sound pressure output is proportional to air density. The threshold of hearing was measured at sea level and 35,000 feet, and no shift in threshold sensitivity was observed.