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BELL SYSTEM TECHNICAL JOURNAL 



of an observer, for the reason that the number articulation decreases 

 very rapidly as the sounds approach the threshold of hearing. As 

 may be seen from Fig. 14, the number articulation passes from practi- 

 cally 100 per cent to per cent in the short range of 10 or 15 db. 

 It is evident that such lists give a critical measure of the point at which 



100 



80 



60 



40 



20 



t------- 



m 



20 40 



SENSATION LEVEL- db 



60 



Fig. 14 — Number articulation vs. sensation level 



an observer fails to hear the sounds. Lists of this type have been 

 used extensively in testing the hearing of school children. 



Summary 



The standard testing technique is primarily a means of determining 

 the articulation or recognizability of the individual speech sounds 

 when they are spoken in a way that is representative of conversational 

 speech, and in a way which facilitates the carrying out of articulation 

 tests. The articulations of the individual sounds may be converted 

 into an index which indicates the speech capabilities of a system. 

 Other types of lists which yield either the recognizability of speech 

 sounds, or the intelligibility of discrete English words and sentences 

 containing thought, have been described and experimentally correlated 

 with the syllable technique. 



It should be emphasized that there may not be a one to one corre- 



