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BELL SYSTEM TECHNICAL JOURNAL 



carrier. Ordinary speech results from a single person producing the 

 message waves and the carrier waves simultaneously in his vocal tract, 

 for then the carrier of speech receives an imprint of the message by 

 modulation. 



The Speech Mechanism as a Circuit 



The foregoing three illustrations by segregating the basic elements 

 in speech production reveal the underlying principles. The present 

 paper treats of these elements as functioning parts of a circuit. In 

 Fig. 1 is shown a cross-section of the vocal system. The idea to be 

 expressed originates in the talker's brain at the left top. Thence, 

 impulses pass through the nerves to the vocal tract with the complete 

 information of the "message," that is to say, what carrier should be 

 used, what fundamental frequency if the carrier is of the voiced type 

 and what transmission through the vocal tract as a function of fre- 

 quency. The carrier whether voiced or unvoiced is shown for sim- 

 plicity as arising at the talker 's vocal cords. This carrier is modulated 

 to form speech having the complete message imprinted on it prepara- 

 tory to radiation from the talker's mouth to the ear of the listener, who 

 recognizes the imprinted message. 



In discussing the speech mechanism as a circuit, it is clearer to start 

 with a block schematic. Figure 2 has thus been drawn to sketch the 



1 IDEA r-i 



I I 



I 1 



I I I 



Fig. 2^The basic plan of synthesizing speech. 



SPEECH 

 WAVES 



basic plan of speech synthesizing. As in Fig. 1, the idea gives rise to 

 the message which modulates the voice carrier to produce the speech 

 radiated from the talker's mouth. One can follow the path of the 

 message from its inception in the talker's brain to its radiation from 

 his mouth as an imprint on the issuing sound stream. The progress 

 of the sound stream is also seen from its origin as an oscillatory carrier 

 to its radiation from the talker's mouth carrying the message imprint.* 

 The light arrow heads indicate direction of flow while the heavy ones 

 indicate a modulatory control of the carrier by the message. This 



■* Here the carrier path is stressed to show the alteration of the carrier sound 

 stream as it proceeds on its way from the point of origin to the point of radiation. 

 This also accords with the importance of the voice carrier which is received and used 

 by the ear, and thus differs from the treatment of the carrier in simple radio 

 broadcast reception. 



