Biology Reference
In-Depth Information
Chapter 6
Sonic Patterns I: The Noise
6.1
Introduction
Noise is a phenomenon that has been observed in acoustic, in visual (image), and
electronic and vibrational (thermal) fields as well. Acoustic noise, in a communica-
tion perspective, is the result of a sound that is not used to communicate and that in
many occasions can reduce the efficiency of direct and remote communications.
White noise and pink noise are examples of two models of noise. The first is
characterized by a constant amplitude of pitches along the frequencies; in the
second, the amplitude is a function of 1/
f
(Fig.
6.1
). In most cases, noise has a
small amount of meaningful information and sophisticated procedures are required
to extract such information.
There is an impressive literature on noise source and propagation in different
media and on the effects of noise in animals and humans. An interesting and
abundant literature considers the possibility to reduce ambient noise from urban
areas but also in natural areas (parks, natural reserves, recreational areas; see
Chap. 10: Applications).
6.2 A Definition of Noise
Noise is an unintentional (mainly from background) sound that masks acoustic
signals and may be generated by geophonies (e.g., strong wind, volcano eruptions,
earthquakes), biophonies (e.g., urban roosting of starlings, breeding colonial birds
and mammals), antrophonies (e.g., urban traffic, oil spill, stationary machines such
as air conditioners). Noise can be generated by a continuous source, such as running
waters, or by a discrete event such as thunder.
The noise may be a random event, such as a car horn, or a regular event, such as
the sound of a bell, repetitive like the jackhammer or unique like a rifle shot. “The
noise of
. an engine, a horn, etc.” means also a sound with a reduced structure in
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