Biomedical Engineering Reference
In-Depth Information
which the relationship between relative velocity
v
of the bodies in contact and friction
force
f
is represented as a differential problem [
4
]. Assuming that friction results
from a large number of microscopic elastic bonds, also called bristles, the velocity-
to-force
f
(...,
v
,...)
relationship is expressed as:
f
(
z
,
˙
z
,
v
,
w
)
=
σ
0
z
+
σ
1
˙
z
+
σ
2
v
+
σ
3
w
(12.2)
where
z
is the average bristle deflection, the coefficient
σ
0
is the bristle stiffness,
σ
1
the bristle damping, and the term
σ
2
v
accounts for linear viscous friction. The fourth
component
σ
3
w
relates to surface roughness, and is simulated as fractal noise.
12.2.3 Walking Sounds and Soundscape Reproduction
The algorithms described in the previous section provide faithful simulations of
walking sound on different surfaces. In order to achieve realistic simulations of
virtual environments, it is important to provide a context to such sounds, i.e., to be
able to render them as delivered in specific locations.
“Spaces speak, are you listening?” asks the title of a topic by Blesser and Salter,
which explores the topic of aural architecture from an interdisciplinary perspec-
tive considering audio engineering, anthropology, human perception and cognitive
psychology [
7
]. Indeed listening to a soundscape can provide useful information
regarding the size of the space, the location, the events happening. The sounds asso-
ciated to a place can also evoke emotions and memories. Moreover, when exploring a
place by walking, at least two categories of sounds can be identified: the person's own
footsteps and the surrounding soundscape. Studies on soundscape originated with
the work of Murray Schafer [
87
]. Among other ideas, Schafer proposed soundwalks
as empirical methods for identifying a soundscape for a specific location. During
a soundwalk it is important to pay attention to the surrounding environment from
an auditory perspective, while physically blocking the input from strong sensorial
modality like vision, by walking blindfolded. Schafer claimed that each place has a
soundmark, i.e., sounds which one identifies a place with.
When reproducing real soundscapes in laboratory settings several challenges are
present, both from the designer's point of view and from the technologist's point
of view. From the designer's point of view, the main challenge is how to select the
different sonic events that combined together produce a specific soundscape. From
this perspective the scientific literature is rather scarce. The approach usually adopted
is merely based on the artistic skills and intuitions of the sound designer. However, an
exception is the work of Chueng [
11
], who suggested to design soundscapes based on
users' expectations. Her methodology consists of asking people which sounds they
associate to specific places, and then use their answers as a starting point to create
soundscapes. Chueng also proposes discrimination as an important parameters in
soundscape design. Discrimination is defined as the ability of a soundscape to present
