164 



BELL SYSTEM TECHNICAL JOURNAL 



the 400-cycle tone and the 200-cycle tone as is evident from the 

 curves. It would be necessary to raise the 300-cycle tone above 16 

 units for it to be heard in the presence of 400 cycles of loudness 50. 

 However, if the sound is magnified without distortion 30 loudness 

 units, so that these three frequencies have loudness values of 80, 40 



Binaural Masking 



$60 



~%20 



PS 



20 40 60 '80 100 120 M 

 Loudness of Fp 



$60 

 "§20 



20 1 "40 60 80 100 1101% 



Loudness of Fp 



$60 



^40 



i.20 



^60 

 % 40 

 §20 



20 40 60 80 100 110 140 



Loudness of Fp 



20 40 60 80 100 120 140 

 Loudness of Fp 



$60 



^40 

 izo 



20 40 60 80 100 120 140 



Loudness of Fp 



20 40 60 80 100 120 140 

 Loudness of Fp 



120 



20 40 60 80 100 120 140 



Loudness of Fp 



■60 

 [40 



$20 



^40 



20 40 60 80 100 110 140 



Loudness of Fp_ 



J 40 



20 40 60 80 100 120 140 

 Loudness of Fp 



^601 f,= 1200 

 ^40 

 §20 



£-4000 



20 40 60 80 100 120 140 

 Loudness of Fp 



Fig. 10 



and 40, respectively, then the 400-cycle tone and 300-cycle tone only 

 will be heard. Under such conditions, the 300-cycle tone could be 

 attenuated approximately 15 units before it would disappear. This 

 means that the sensation produced by a complex sound is different in 

 character as well as intensity when the sound is increased or decreased 

 in intensity without distortion. In general, as the tone becomes 

 more intense the low tones become more prominent because the high 



