In trying to identify the various sources of noise, one immediately thinks of the din
that characterizes modern cities. In fact, a major emphasis has been placed on community
sound studies in urban areas (5–10). This owes to the demonstrable fact that urban
areas are generally noisier than rural areas, and because larger numbers of people live
in urban areas, where they are presumably affected by the noise, the benefits may be
expected to be proportionally larger. Urban noise levels are a complex mixture of noise
from transportation, factories, industries, machines, and people. Basically, noise sources
can be grouped into three types: transportation, industrial, and residential.