CARRIER NATURE OF SPEECH 505 



there is an altering of speech frequencies as in frequency modulating 

 circuits; and finally, there is an amplitude modulation to yield a se- 

 lective transmission of the various carrier components of the voice. 

 However, the voice mechanism differs from the usual carrier circuit 

 markedly as regards complexity. In the voice mechanism there are 

 two types of carrier each with a multiplicity of partial carrier com- 

 ponents. The incoming message has a multiple nature. Finally, 

 several modulations take place including both amplitude and frequency 

 types. This multiplicity of carrier relations indicates the wide range 

 of voice phenomena possible. 



Any electrical speech synthesizer must be a functional copy of the 

 human speech synthesizer in providing the essential speech character- 

 istics sketched in the preceding paragraph. There have been devel- 

 oped two such electrical synthesizers referred to in the introduction. 

 A brief description of these will be given followed by some circuit 

 comparisons. 



These electrical synthesizers are known as the vocoder and the 

 voder. The vocoder was so named because it handles the speech in a 

 coded form ; the voder, because it serves as a Voice Operation DEmon- 

 stratoR. Considerable interest has been manifested at the public 

 showings of each of these synthesizers, the vocoder in a limited number 

 of lecture demonstrations and the voder at the San Francisco and New 

 York World 's Fairs. Circuit details have been published elsewhere.^ 



Of these two speech synthesizers the vocoder was constructed first. 

 It works on the principle of automatically remaking speech under 

 control of spoken speech instantaneously analyzed to derive the code 

 currents for the control. The vocoder as set up for demonstration is 

 shown in Fig. 4. 



The voder was derived from the vocoder by substituting manipula- 

 tive for automatic controls. The resulting voder as displayed at the 

 New York World's Fair is shown in Fig. 5. In the Fair demonstration, 

 repeated continuously at intervals of about five minutes, the male 

 announcer gives a simple running discussion of the circuit with the 

 girl operator replying to his questions by forming sounds on the voder 

 and connecting them into words and sentences. She does this by 

 manipulating fourteen keys with her fingers, a bar with her left wrist 

 and a pedal with her right foot. This requires considerable skill by 

 the operators. The vocoder, automatic in nature, presents no problem 

 of operating technique. 



' The vocoder in the Jour. Acous. Soc. Amer., Vol. 11, pp. 169-177, October 1939, 

 "Remaking Speech," Dudley; the voder in the Journal of the Franklin Institute, Vol. 

 227, pp. 739-764, June 1939, "A Synthetic Speaker," Dudley, Riesz and Watkins. 



