Biomedical Engineering Reference
In-Depth Information
environment generating an auditory feedback as result of actions. This last situation
ideally represents the scenario with augmented footstep sounds, where each step
of the user must be tracked and rendered while the user is walking in the virtual
environment, without any perceivable latency, in order to recreate for example the
illusion of walking on a surface different from the one the user is actually stepping
upon, or to allow the user to interact with objects of the virtual environment.
Sound delivery using headphones can also be performed using two general
approaches: the simple mono or stereo delivery and a solution based on binaural syn-
thesis. One of the main issue in combining footstep sounds and soundscape design
is to find the right amplitude balance between the two. One approach can be empir-
ical, by asking subjects to walk freely while interactively producing the simulated
footstep sounds and hearing the reproduced soundscape through multichannel speak-
ers. Subjects are then able to adjust the volume of footstep sounds until they find a
level which they considered satisfactory. After describing the possibilities offered by
hardware technologies, the next section describes available software packages for
footstep sound design.
12.2.4 Footstep Sound Design Toolkits
A specific treatment on the use of the above models for foot-floor interaction pur-
poses has been presented by Serafin et al. [
88
], along with pointers to sources of
software, sound, and other documentation material. Implementing such models is
not straightforward, but real-time software modules realizing impact and friction
interactions are available, that are open and flexible enough for inclusion in more
general architectures for the synthesis of footstep sounds. In particular, the Sound
Design Toolkit
1
(SDT) [
21
] contains a set of physically-consistent tools for design-
ing, synthesizing and manipulating ecological sounds [
36
] in real time. SDT consists
of a collection of visual programs (or
patches
) and dynamic libraries (or
externals
)
for the software Puredata, which is publicly available, and Max/MSP, which is easier
to work with although commercial. SDT provides also examples, allowing users to
launch these patches and see them at work in both such visual environments.
Public software is also available, which implements footstep sound synthesis
models that are ready for use. Farnell accompanied his work with a patch and an
external for Puredata, both referenced in the related paper [
27
]. Fontana's crumpling
model for Puredata has been integrated in SDT: examples of this model at work can
be found, among others, in the Natural Interactive Walking project website.
2
The
same website collects sound examples resulting from alternative instantiations of
the physically-based approach, based on a sound synthesis engine that has not been
put available in the public domain [
102
]. Furthermore, it contains footstep sounds
that have been generated using the aforementioned hybrid model descending from
Cook's synthesis technique.
1
2
