Effects of Distortion on the Intelligibility of Speech at High Altitudes
George Armitage Miller, Stouf- F Er Mitchell · The Journal of the Acoustical Society of America · 1946
Sounds spoken into the closed cavity of an oxygen mask at high altitudes differ substantially in quality and intensity from normal speech at sea level. The mask imparts a low, “booming” quality to the speech. Tests with a wide variety of frequency response characteristics show that low-frequency attenuation improves the apparent quality without modifying appreciably the intelligibility of the speech. Also, the intensity of the speech signal varies considerably as a function of altitude, and talkers exhibit large individual differences in their ability to compensate for altitude effects. The range of speech levels under all conditions of altitude and talker differences is between 20 and 30 db, and for most installations some form of compression should be used to reduce this range. Sharp, symmetrical limiting (“peak clipping”) is the most satisfactory method, since it combines the advantages of compression with the advantages of premodulation peak clipping for AM radio-telephony.