392 



BELL SYSTEM TECHNICAL JOURNAL 



40 



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120 

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 20 

 



120 



100 



I 



I 



, 80 

 I 



I 60 



u 



Z 40 



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20 40 60 80 100 120 



INTENSITY LEVEL-DB 



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I INTENSITY LEVEL-DB j 



Fig. 2 (E to J) — Loudness levels of pure tones. 



