Applications - Soundscape Ecology: Principles, Patterns, Methods and Applications - page 288

sonic sources are available, the use of a stream analysis can improve the perceptual
process. Spatial separation can help a listener to distinguish two pieces of similar
acoustic information according to the position in space from which the two
sources come.
After an auditory display is heard and streamed, it is absolutely necessary to
attribute the meaning. For this, it is necessary to reduce the ambiguity; for example,
the listener must recognize a fire from a depressurization or by the presence of toxic
substances.
To optimize the design of an acoustic display it is important to fix some
parameters such as loudness, pitch, masking, interacting dimensions, tempo and
rhythm, timbre, pain and fatigue, spatial location, and streaming.
Loudness or perceived intensity is the first acoustic approach to a sound. A
correct design should maintain this attribute in a way that can be strong enough to
communicate but not too much to damage the auditory display.
Masking is the effect by which a sound is shaded by the background noise or by
another sound. This is a well-known problem in bioacoustics where animals are
often in competition for the sonic environment.
Pitch is one of the most used auditory display dimensions for the ease with
which it can be manipulated and perceived. Pitch is less influenced by the sonic
environment than loudness. The human hearing capacity ranges from 20 to
20,000 Hz, and the optimum ranges between 80 and 10,000 Hz. The sensitivity to
pitch change is highest at 3,000 Hz, and for this reason the acoustic display is
optimized for working between 200 and 5,000 Hz.
Interacting dimensions refers for instance to the relationships between pitch and
loudness.
Tempo (from Latin, tempus: time) is the speed of music or any sequence of
sounds. Traditional tempo indications are given in Italian, ranging (from slow to
fast) as largo, adagio, andante, moderato, allegro, presto, prestissimo .
Tempo has been used for instance in the Geiger counter in which the change of
tempo is related to the increase of radioactivity.
The discrimination between periodic and aperiodic events can be easily obtained
by people with changes in temporal frequency of sounds.
Timbre refers to the properties of sound that cannot be expressed in loudness,
pitch, or tempo. The capacity to distinguish sounds with different timbres is
important for the auditory display. Timbre concurs to the completeness and effi-
ciency of the auditory display.
Pain and fatigue have to be eliminated in every auditory display, of course, but
often it is not easy to find the better threshold and connected trade-off. People in
general reduce their acoustic attention after half an hour and this is important in
auditory design.
Spatial location. The creation of artificial spatiality of sound is today a common
technique in movies. The spatiality of sound source facilitates their identification or
selection. The psychoacoustic research has established that spatial discrimination
varies with angular resolution (1-2 of azimuth in the front, and 5-6 to the side).
Differing from vision, sound perception does not requires that the listener be