Building codes throughout the United States require a measure of sound insulation between floors of multi-family dwellings. They specify a minimum architectural design standard of privacy of 50 STC (Sound Transmission Class) and a 50 IIC (Impact Isolation Class). The codes also state that validation of the minimum noise criteria can be field measured and the field measurements shall not be less than a 45 FSTC or a 45 FIIC.

Of course, contractors sometimes find ways to cut corners. But in general, neighbor-noise is a solved problem.