The Effects of High Altitude on Speech

The effects of altitude on the human voice have been determined by measuring speech spectra as a function of altitude. The apparatus simultaneously recorded the square of the sound pressure in twelve contiguous bands extending from 60 to 9000 c.p.s. Eleven talkers were used, and data were obtained in a decompression chamber at constant temperature for altitudes up to 40,000 feet. Special attention was given to the method of monitoring and phonation. Vowels, sibilants, words, and connected speech were used as test material. The results indicate that vowels and semi‐vowels exhibit a loss in mean square pressure with altitude roughly proportional to the logarithm of the density ratio, while some consonants are little affected by altitude. Measurements indicate that the number of words spoken on one breath of air is proportional to air density if constant sound pressure output is required. Normally, at 35,000 feet, it is necessary to pause for breath about two to three times as frequently as at sea level.