ARTICULATION TESTING METHODS 



821 



the same circumstances, the probable error for the average syllable 

 articulation is ± 2, and that for the sound articulation is ± 1. 



Control of Practice Effects 



The third factor entering into the reproducibility of articulation 

 results is practice and experience. The practice effect manifests itself 

 in various ways. An increase in articulation takes place as the 

 observers become more familiar with the vocal characteristics of the 

 speakers. Similar effects are observed as they become more accus- 

 tomed to a given technique, or to a particular type of distortion. 

 In general, these effects become smaller as the testing crew becomes 

 more experienced. 



100 



100 



24 32 40 



NUMBER OF TESTS 



24 32 40 



NUMBER OF TESTS 



Fig. 2 — Typical growth curves 



Fig. 2 shows several typical growth curves that were obtained in 

 the process of training new crew members. In this process the new 

 members observe continually on various circuits until the results 

 compare favorably with the results that are obtained by experienced 

 observers. In such tests, experienced speakers are used. The aver- 

 ages for two new observers, of the results that were obtained on a 

 high grade circuit, are shown by Curve I. Two speakers were used 

 in these tests. A limited amount of testing was done by the observers 

 prior to the above tests. Upon the completion of the tests of Curve I 

 about 30 or 40 additional tests were made on various circuits. A 

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