As a very junior member of the Rolls Royce Hucknall Flight Test Establishments staff in the 1970's working in the Noise Department we struggled to reduce noise emissions. With the introuduction of RB 211 we made real inroads into the problem. Forty years downstream I can still recall my introductory notes.
Public reaction to 'noise' is dependent on several variables
- Frequency as in an emitted frequency
- Duration
- Pitch
In the very broadest of terms the higher frequencies, particulaly of longer durations are the more annoying.
Atmosphere does attneuate to a greater degree than you might think. Wet draggy misty conditions acting as an efficient muffler