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BELL SYSTEM TECHNICAL JOURNAL 



articulation tests of direct speech from an individual and its repro- 

 duction by the artificial voice agree within a few per cent. The design 

 can be definitely specified and reproduced with accuracy and it is 

 rugged in structure and constant in performance. 



General experience in the use of this artificial voice over about a 

 year's time has indicated that it may be used satisfactorily in forms 

 of transmitter testing which have heretofore required the human 

 voice. 



500 1000 



FREQUENCY IN CYCLES PER SECOND 



10,000 



Fig. 9 — Effect of introducing station transmitters in sound field of artificial mouth. 



The Artificial Ear 

 The human ear is limited in its utility generally to relative or com- 

 parative measurements, and is not well adapted for measurement of 

 absolute pressure or velocity. At best, measurement with real ears 

 is a laborious procedure. In general, it has been found necessary to 

 take a large number of observations with many ears, since a measure- 

 ment with one ear is unreliable. One of the principal reasons for this 

 unreliability is the difliculty not only of securing a particular coupling 

 of a receiver held to the ear, but of duplicating this coupling in sub- 

 sequent measurements. 



