Biomedical Engineering Reference
In-Depth Information
few easily identifiable soundmarks. In her approach, this is also called minimal
ecological sound design.
Studies have shown the importance of auditory cues in virtual reality simulation,
and how they can lead to measurable enhancement in what is called the feeling of
presence. In [
86
] it is reported how sound contributes to user's sense of presence, as
evidenced by electrodermal activity and temperature measurements, as well as ques-
tionnaire's scores. Moreover, significant differences were noticed when measuring
delivered sound through headphones or surround sound (5.1) using loudspeakers.
Other studies show how ratings of presence are enhanced by either the addition of
bass or the increase of volume. On the other hand, an increase on number of chan-
nels does not increase ratings of presence [
32
]. The role of self-produced sounds to
enhance sense of presence in virtual environments has also been investigated. By
combining different kinds of auditory feedback consisting of interactive footstep
sounds created by ego-motion using the techniques described in the previous section
with static soundscapes, it was shown how a person's motion in a virtual reality
environment is significantly enhanced when moving sound sources and ego-motion
are rendered [
74
].
Concerning delivery of footstep sounds, they can be conveyed to the walker by
means of different hardware devices, such as headphones, loudspeakers or through
bone conduction. The choice of delivery methods depends on several factors, for
example if the soundscape has to be part of a mobile or augmented reality instal-
lation, or if it is part of a virtual reality laboratory setting. An ecologically valid
solution consists of placing loudspeakers at the shoes' level, since this faithfully
reproduces the equivalent situation in real life, where footstep sounds come at the
level of the interaction between a shoe and a floor. As an alternative, sounds can be
conveyed by means of a system of multichannel loudspeakers. In this case a problem
arises regarding how footstep sounds can be rendered in a 3D space, and how many
loudspeakers should be used and where they should be placed.
Sound rendering for virtual environments has reached a level of sophistication
that it is possible to render in realtime most of the phenomena which appear in the
real world [
34
]. 3D spatialized audio in immersive virtual environments remains
however still challenging. In delivering through multichannel speakers, the choice
of rendering algorithms is fundamental. As a matter of fact, various typologies of
soundscapes can be classified: static soundscapes, dynamic soundscapes and inter-
active soundscapes. Static soundscapes are those composed without rendering the
appropriate spatial position of the sound sources. In static soundscapes the same
content is delivered to every channel of the surround sound system. The main advan-
tage of this approach is the fact that the user exploring the virtual environment does
not need to be tracked, since the same content is displayed to every speaker no
matter where the user is placed. The main disadvantage is the fact that the simula-
tion does not represent a real life scenario, where different sonic cues are received
depending on where a person is placed. Dynamic soundscapes are those where the
spatial position of each sound source is taken into account, as well as their eventual
movements along three-dimensional trajectories. Finally, interactive soundscapes are
based on the dynamic ones where in addition the user can interact with the simulated
