660 



BELL SYSTEM TECHNICAL JOURNAL 



10 



20 30 40 50 



NOISE METER READINGS IN db 



60 



70 



Fig. 4 — Results of noise meter measurements of noise in business locations. 



10 



10 



20 30 40 



WARBLER READINGS 



50 60 70 



•THRESHOLD SHIFTS IN db 



80 



Fig. 5 — Results of measurements of noise in business locations by masking method. 



