Methods - Soundscape Ecology: Principles, Patterns, Methods and Applications - page 219

Capturing the physical sound means to collect under a digital format the

numerical value of the sound at a precise temporal interval.
In terms of sound measurements we have to distinguish between

(a) sound pressure investigation and
(b) spectral investigation.

Sound pressure is measured using a calibrated sound meter or phonometer that
measures the sound pressure level (SPL). This measure is commonly used for the
quantification of different kinds of noise/sounds, especially for industrial and
environmental noise.
The spectral measure is obtained by recording sounds with microphones, storing
the data in digital format in memory mass storage devices (e.g., external hard disk
drive), and processing the data by applying, for instance, the Fourier transform
procedure.

9.2 Basic Elements of Acoustics

To allow the reader to fully understand the terminology adopted in this topic, we
have considered it essential to report a summary of the fundamentals of acoustics
necessary to develop our reasoning before describing some methodologies in
soundscape analysis. This fundamentals do not represent an exhaustive treatment
of acoustic terms but some essential synthetic and incomplete references.

9.2.1 The Sound

Sound is produced by a rapid variation in the average density or pressure of air
molecules above and below the current atmospheric pressure. Sound is defined by
The American Heritage Dictionary of the English Language (fourth edition, 2000)
“ as a vibration transmitted through an elastic solid or a liquid or gas, with
frequencies in the approximate range from 20 to 20,000 hertz, capable of being
detected by human organs of hearing ”.
Sound can be also defined as a sequence of waves of pressure that propagates
through compressible media such as air, water, or soil in a process of compression
and rarefaction. The changes in atmospheric pressure originated by a vibrating
device produce a sound pressure, and the fluctuations create sound waves.
Humans perceive sound from approximately a minimum threshold of 20 μ Pa

10 6 Pa) to 100 Pa (the threshold of pain) (~140 dB). The smallest percepti-
ble change in sound is about 1 dB.

(20