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experience by immersing the user in the gameplay
or VR scene. These types of sounds at present are
still used mostly as effects rather than as authen-
tic references to the virtual landscape. Accurate
spatialization and real-time interactive sonic ele-
ments are essential if the user-experience is to be
brought to the next level in future developments.
Many of the recently developed audio tools
are based on well-established theory, but remain
limited in their implementation of true spatial
sound by hardware constraints. Some of the theory
that has been successfully implemented to varying
degrees are techniques such as Interaural Time
Difference (ITD), Interaural Intensity Difference
(IID), the Doppler Shift, and Distance Attenuation.
However, many more spatial attributes remain dif-
ficult to render in real-time, such as high fidelity
simulation of ear geometrics and head/shoulder
shadow.
As mentioned earlier, some of the basic prin-
ciples and techniques are now readily available
to developers, but the underlying theory in this
field indicates that for true spatial sound to be
delivered to the listener, individualization
1
of the
listening experience is key to its success. Despite
the advances in hardware in recent times, all of
the current spatialization techniques used within
gaming and VR environments remain focused on a
generalized listening experience, and, as of yet, no
commercially viable method has been successfully
implemented that achieves true individualized
spatial sound. The generation of individualized
Head Related Transfer Function (HRTFs) for
commercial dissemination is one of the remaining
milestones to be affected by hardware limitations.
Many in the industry argue that generic solutions
are sufficient in achieving an accurate sense of
immersion in virtual environments for most users.
This argument may well indeed hold true, except
for the fact that it cannot truly be tested until we
can compare it to individualized spatial sound on
a commercial scale.
In addition to the limitations of implement-
ing individualized spatial listening, there still
persists the problem of rendering accurate room
and outdoor acoustics. This is, again, down to
the constraints of available hardware resources.
Rendering what may be considered a simple scene
in the visual domain could easily entail several
very complex models of various acoustically
dependent elements. For example, an accurate
rendition of the listener closing a room door
would need to model the room itself, the door's
material and structure, and the change in acoustic
space during the act of closing the door (from a
coupled space to a singular space). In addition,
other very important factors such as the material
on the floor, walls and ceiling, and reflective and
absorbing objects within the space also need to be
modelled. All this, of course, in real-time!
In spite of the current limitations to imple-
menting commercial solutions for individualized
spatialization, the industry is employing very
interesting and creative workarounds. It has not
only tackled the distribution of sound in virtual
space intuitively, but it has also efficiently tackled
problems relating to large audio data file sizes and
bandwidth. Therefore, in this chapter, not only do
we review sound spatialization techniques, but in
tandem, we also discuss audio compression tech-
nology and how this theme goes hand-in-hand with
spatialized sound for VR and computer games.
PErcEPtUAL PrOcEssING
OF sOUND
The cognitive mechanisms involved in the aural
perception of space are highly evolved and com-
plex, and can be categorized into two distinct
groups-direct analyses of physical/sensory in-
formation, and higher cognitive influences (see
Figure 1). Both groups play a crucial role in our
everyday hearing processes. Even in cases of
perceived silence, background noise stimulates
auditory spatial awareness by communicating
spatial information about the surrounding environ-
ment to the listener based on both acute sensory
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