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BFXL SYSTEM TECHNICAL JOURNAL 



from any one of several sources throu^di the electrical network and 

 amplifier to the electro-acoustic transducer. For single-frequency 

 measurements a heterodyne oscillator provides a convenient means for 

 obtaining the desired testing currents. As a source of speech, ad- 

 vantage can be taken of recent developments in phonograph technique 

 which make it possible to record and reproduce speech practically 

 without distortion.^ This affords a very satisfactory source of speech 

 for the artificial voice. In certain special instances where it is desired 

 to make measurements with human voices under closely controlled 

 conditions, a high quality transmitter is used as the input element of 

 the artificial voice. 



To insure proper operation under both steady-state and transient 

 conditions the electrical network employed in the artificial voice is of 



SINGLE 

 FREQUENCY 

 OSCILLATOR 



HIGH QUALITY 

 TRANSMITTER 



Fig. 1 — Schematic arrangement of artificial voice. 



the constant-resistance type.- In this network is included com- 

 pensation for deviation from uniformity of response of the electro- 

 acoustic transducer. Additional compensation may be provided in case 

 the input to the artifical voice is from a source of constant output with 

 frequency and it is desired to weight the single frequency output of the 

 artificial voice in accordance with the distribution in speech •'' of pres- 

 sure w'ith frequency. 



The amplifiers employed have high gain and high output capacity. 

 They provide, without introducing distortion, the maximum amount 

 of electrical energy that may be required to obtain the desired 

 acoustical output from the artificial mouth. 



' "\'ertical Sound Records — Recent Fundamental Advances in Mechanical 

 Records on Wax." Presented by H. A. Frederick at Swampscott, Mass., Oct., 1931, 

 before the Soc. of Motion Picture Engineers. 



-"Distortion Correction in Electrical Circuits with Constant Resistance Re- 

 current Networks," Otto J. Zobel, Bell System Technical Journal, July, 1928. 



^"Some Physical Characteristics of Speech and Music," Harvey Fletcher, Bell 

 System Technical Journal, July, 1931. 



