Sound is a main mean of communication and entertainment and is also very effective alarm system for some animal. A loud and unwanted or unpleasant sound causes discomfort and is called noise.
The release of unwanted sound in the atmosphere is called noise pollution.
The unit of sound level is decibel (dB). Noise level can range from 0 to more than 120 dB. Noise beyond 120 dB cause discomfort. The intensity of normal conversation sound range between 35 dB to 60 dB.