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frequency composition. The masking effect of the noise on the middle 

 band was greater than that on the high and low bands. In order to 

 give an approximate interpretation of this in terms of pressures in var- 

 ious frequency regions, account must be taken of the relative magni- 

 tudes of threshold pressures in the three warbler frequency bands, since 

 the masking effects were obtained by subtracting threshold settings of 

 the attenuator from the settings made in the presence of the noise. For 



■10 



+10 +20 



NOISE METER READINGS IN db 



30 



Fig. 6 — Results of noise meter measurements of noise in residence locations. 



the middle and upper bands, threshold pressures are about the same; 

 hence, the lower values of masking for the high range indicate that com- 

 ponents in this range are in general relatively weak. As previously 

 determined,^ threshold pressures at frequencies in the low band are 

 several decibels higher than those in the other bands. Combining the 

 values of masking for the low and middle bands with the corresponding 

 threshold pressures, it is seen that the physical magnitudes of compo- 



* H. Fletcher, "Useful Numerical Constants of Speech and Hearing," Bell System 

 Tech. Jl., July 1925. 



