Sound Ledger: Noise in Three Cities

38.69: Mean number of decibels in Oklahoma City, Oklahoma, which has been judged the quietest large city in the United States 

4: Number of decibels the city of Paris hopes to cut as it tackles noise pollution

21,000: Estimated number of noise complaints about aircraft made by one Perth resident over the course of a year

Sources: Oklahoma: insidermonkey.com; Paris: msn.com; Perth: thewest.com.au.