Biology Reference
In-Depth Information
According to a soundscape perspective, noise can be defined as the portion of the
acoustic spectrum that does not offer information per se, but the amount of noise
and its distribution in time can be used to assess natural or anthropogenic events and
to attribute a sonic quality to a landscape or to a site/location (see Fig. 4.9, page 87
as an example of environmental noise source).
Noise remains a not-clear concept that is used often to define every anthropo-
genic sound or and unwanted sound. We prefer such last definition because, for
instance, if you wish to talk at a cell phone inside an exhibition of caged birds,
immediately you realize it is not an appropriate location and it is not easy to
communicate, although each bird produces a lovely song.
If we consider noise in the physical sense, in nature the noise is a rare event when
there is no direct or indirect human intervention. But again, does a waterfall or a
wind tempest produce sounds or noise? This question remain unanswered.
From a semiotic point of view, a waterfall can be considered a sonic landmark
for some species and simply a noise for others.
When animals are engaged in dawn or dusk choruses, because of the contempo-
rary song activity we perceive such choruses as an indistinct noise. The same is true
for urban noise that is the product of road traffic, human voices, horns, bells, air
conditioners, etc.
6.3 Characteristics of Anthropogenic Noise
Humans are the major factor responsible for increasing noise pollution. Noise has
no boundaries, is difficult to be managed, and becomes chronic in urban areas and
close to the great transportation infrastructures (Barber et al.
2009
).
There is industrial noise, urban noise, ambient noise, aircraft noise, etc., and
often noise is considered at the same level of importance of chemical substances as
a source of pollution.
The transportation net is one the major sources of ambient noise, and air and road
transport are so intense worldwide that entire ecosystems are exposed to growing
chronic noise.
6.4 Active Space and Noise
Active space (AS) is defined as the distance from the sender at which a signal can be
detected by a receiver. The AS depends on the quality of the signal, the level of
noise that masks this signal, and the critical ratio of the receiver's sensory system.
The critical ratio (CR) is the lowest level of a signal (in dB) at which the signal is
detectable. The CR varies according to frequencies and across species.
Phase and time of signals are deeply modified by noise. Noises characterized by
low frequency and high amplitude are good candidates to mask acoustic signals.
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