Image from page 520 of "The Bell System technical journal" (1922)
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ular actions in the vocal tract. Never-theless these motions contain the dynamic speech information as isproved by their interpretation by lip readers to the extent visibilitypermits. Another method of demonstrating the information contentof certain of these motions is the artificial injection of a sound streaminto the back of the mouth for a carrier whereby intelligible speech 2 The information referred to is that in the communication of intelligence. Thereis, however, static information in the carrier itself. This serves for station identi-fication in radio and may similarly help in telling whether it was Uncle Bill orAunt Sue who said ah. CARRIER NATURE OF SPEECH 497 can be produced from almost any sound stream. The need of anaudible carrier to transmit this inaudible message is obvious. The final example, to illustrate the modulating mechanism in speechproduction, is from a person talking in a normal fashion. In thisexample are present the message and carrier waves of the previous
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r/////// CARRIERCORD TONE OF VOICED SOUNDSBREATH TONE OF WHISPER STEADY AIRSUPPLY Fig. 1—The vocal system as a carrier circuit. examples, for both are needed if the former is to modulate the latter.However, the mere presence of the carrier and message waves will notmake speech for if they are supplied separately, one by a silent talker andthe other by an intoner, no speech is heard but only the audible intoned ^ R. R. Riesz, Description and Demonstration of an Artificial Larynx, Jour.Acous. Soc. Amer., Vol. 1, p. 273 (1930); F. A. Firestone, An Artificial Larynx forSpeaking and Choral Singing by One Person, Jour. Acous. Soc. Amer., Vol. 11,p. 357 (1940). 498 BELL SYSTEM TECHNICAL JOURNAL carrier. Ordinary speech results from a single person producing themessage waves and the carrier waves simultaneously in his vocal tract,for then the carrier of speech receives an imprint of the message bymodulation. The Speech Mechanism as a Circuit The foregoing three illustrations by segregating
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