PROCEEDINGS of the23rd International Congress on Acoustics
9 to 13 September 2019 in Aachen, Germany

Interactive soundscape augmentation of an urban park in a real andvirtual setting
Timothy VAN RENTERGHEM1; Kang SUN1, Karlo FILIPAN1,2, Kris VANHECKE1,3, Toon DE
PESSEMIER1,3, Bert DE COENSEL1,2, Wout JOSEPH1,3, Dick BOTTELDOOREN1
1Ghent University, WAVES research group, Department of Information Technology, Belgium
2ASAsense cvba, Bruges, Belgium
3IMEC vzw, Leuven, Belgium

ABSTRACTInappropriate soundscapes are able to strongly deteriorate the user experience in parks. A possible
remediation is adding positively perceived sounds. The case of an urban park, fully surrounded by road traffic
noise sources, was studied to explore the potential of adding natural sounds in an interactive way. A
preliminary test was conducted in the lab with Virtual Reality (VR) glasses and headphones. The audio-visualrepresentation of the real environment was obtained by combining binaural recordings with first-orderambisonics and 360-degree video camera footage. The users were allowed to mix in eight types of naturalsounds until their personal optimized soundscape was composed. This was done in a very similar setup as inthe (real) park. The loudspeaker augmenting the sound environment in the park was steered with asmartphone application. This app ensured the user’s presence near the loudspeaker and allowed to gather
more detailed assessments of the perceived sound environment through questionnaires. This combination ofexperiments allowed checking the validity of VR that is becoming increasingly popular in audio-visualinteraction studies. In addition, the most preferred natural sounds and the way they influenced environmental
noise perception were analyzed.
Keywords: Soundscape, Virtual Reality, Augmented Reality.

1. INTRODUCTION
When well designed, urban parks are able to provide multiple ecosystem services. Of major
importance for people living in city centers are the social and health related benefits (1). However,these can be jeopardized by excessive or inappropriate sound exposure. Especially the abundance of
mechanical sounds in cities might strongly deteriorate these services for citizens.
Sound levels inside parks could potentially be mitigated in a natural way e.g. by placing dense tree
belts near the borders (2) or by so-called “acoustical landscaping” (3). However, this conflicts withmany design criteria for the other park functions; visually dense or non-transparent parks might e.g.
give rise to perceived unsafety (4).
An alternative is relying on the soundscape idea (5). Instead of trying to mitigate unwanted sounds,
positive sounds are added. Obvious candidates in park environments are natural sounds. In this study,
various types of bird sounds, insects, water sounds and meteorologically induced sounds have been
considered. The question remains what types of sounds and what combinations are most suited andpreferred by the park visitors. The latter was studied in an interactive way.
Virtual reality is increasingly becoming popular in landscape and city planning. The question
remains, however, to what extent a park experience can be captured. In this work, this researchquestion is narrowed down to analyzing whether the preferred natural soundscape in a virtual setting issimilar to the one found in the real park.
The case of interest is the Zuidpark in Gent (Belgium), an urban park with an open character,surrounded by intense road traffic. Continuous sound pressure level measurements during 5 months
showed an L den value of 62.6 dBA. The Lday indicator in this same period equaled 60.4 dBA.
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timothy.vanrenterghem@ugent.be899

2. VIRTUAL REALITY (VR) EXPERIMENTThe audio-visual representation of the park environment is based on a combination of binaural
recordings with first-order ambisonics and 360-degree video camera footage (6). For visual
representation, an Oculus Rift was used. The environmental sounds from the park were reproducedwith an open headphone. The setup allowed to mix in the natural sounds played by a loudspeaker thatwas positioned roughly at the same height and distance as in the real park environment. Theparticipants could control a mixing panel (with mechanical sliders) while composing their preferredsoundscape based on the eight available natural sound samples. This test was performed in asemi-anechoic room as shown in Fig. 1. In this preliminary test, the number of participants werelimited to 10.

Figure 1 – Experimental setup for virtual reality experiment in the semi-anechoic room.

3. AUGMENTED REALITY (AR) EXPERIMENTIn the real park, the loudspeaker was hidden from sight by the vegetation (see Fig. 2). Participants
were instructed to move to a specific zone close to the single-board computer (SBC) operating theloudspeaker. The experiment could be accessed at any moment during the day hours and – in theory no instructor guiding the experiment was needed.
Environmental sound pressure levels were continuously monitored close to the loudspeaker box.
This will allow a more thorough analysis of the interaction between the soundscape composition andthe momentary (background) sound field.
3.1 Android app
Interaction with the loudspeaker box was performed by an Android app on the personal smartphone(see Fig. 3). The SBC served as a local Wi-Fi access point. This connection allowed to control theloudspeaker and to log the answers to the questionnaires and other usage statistics. When theparticipant went outside the range of the Wi-Fi access point, the session stopped. This principle
confined the participants to a limited zone and ensured that they could actually hear the sounds played.
3.2 Tasks and questionnaires
The smartphone app not only served as a mixing panel to augment the sound environment withnatural sounds, but also for sending a number of small questionnaires to the respondent .
First, each participant was instructed to listen to the current background noise for a t least one
minute. Next, a question was asked regarding the general appreciation of the sonic environment, somespecific soundscape related questions (5), and also to what extent specific environmental noise sources
could be heard.
Secondly, the user was asked to rate a random soundscape, previously composed by another900

participant. The minimum listening time was set to 1 minute. The same set of questions related to thebackground noise was asked afterwards.
Thirdly, the user was invited to compose their own preferred soundscape for the current
environment. The natural sounds that could be added (using a software mixing panel, see Fig. 3) were
not named as some might have a positive or negative connotation. When finished, the volume settings
were stored on the SBC, and the soundscape was added to the database and could potentially bepresented to future users.

Figure 2 –Designated location to participate in the interactive soundscape experiment in the (real) park.

Figure 3 – Some screenshots of the soundscape smartphone app.

4. RESULTS
4.1 Preferred soundscapes
The current analysis is based on 58 participants that successfully finished a complete session in thepark (see Section 3.2). The average volume setting (between 0 = mute and 1= maximum level), over allparticipants, is shown in Fig. 4. Although such preference inevitably leads to rather large interpersonalvariation, some clear trends can nevertheless be observed. Bird sounds, more specifically “song birdsmixture” and “house sparrows”, are the most preferred natural sounds in the urban park. This isconsistent with older research (see e.g. Ref. 7). “Sea gulls”, in contrast, are much less wanted,probably by a bad connotation and being less congruent with the current environment (no nearness of901

the sea-side). The “waterstream” is somewhat more preferred than the “falling water” (consistent e.g.
with Ref. 8). “Rustling leaves” and “raindrops on vegetation” are less chosen, probably given that theirspectrum is more noise-like and coincides too much with the background noise. The bird sounds, incontrast, operate in a frequency range (3-6 kHz) that easily reaches a good signal-to-noise ratio in thepark. In addition, these sounds are intermittent and thus more easily attract attention (9).
The preliminary test (with 10 participants), based on a virtual representation of the same spot in thepark, gives a more or less similar averaged set of volume settings (see Fig. 4).

Figure 4 – Averaged volume settings of the composed soundscapes over all participants. The error bars
indicate the 95% confidence intervals on the means, assuming a normal distribution of the data. For
comparison, the red line indicates the averaged channel volumes in the VR experiment.
4.2 Effect of soundscape on general appreciation of the sound environment
The use of soundscapes to improve the acoustic environment is analyzed by subtracting the rating
after listening to the background noise from the rating after being exposed to a random soundscape.
Such a relative comparison removes interpersonal differences in absolute rating level, strongly
increasing the power of the statistical analysis.
For the absolute scales, the following categories were used in the survey (“How would your rate thesound environment you just experienced?”): 1=”very bad”, 2=”bad”, 3=”neither good nor bad”,4=”good”, 5=”very good”. For the pairwise differences, 0 means staying in the same category, e.g. +2
means jumping over 2 classes (e.g. from “bad” to “good”), and -2 resulting in a worsened situation.
Figure 5 depicts the histograms showing the absolute (left, middle) and relative (right) ratings.
The overall appreciation of the sound environment is on average improved by any naturalsoundscape with 0.6 units. This improvement is statistically significantly different from 0 ( t 56=3.5189; p<0.001) with 95% confidence intervals between 0.26 and 0.94.

Figure 5 – Histograms showing the general evaluation of the sonic environment.

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4.3 Effect of soundscape on hearing traffic noise
A similar analysis (see Fig. 6) was performed for the question to which extent traffic noise washeard. Again, a 5-point scale was used, with 1=”not at all”, 2=”a little”, 3=”moderately”, 4=”a lot”,
5=”dominates completely”. Because of the soundscape, a shift of 1.33 units towards less hearing
traffic was observed in a paired t-test (t 56= 8.961, p<0.001). The 95% confidence interval ranged from1.04 to 1.63. These results show that augmenting the current environment with a natural soundscape
has a strong masking potential on road traffic noise.

Figure 6 – Histograms showing the degree at which traffic noise is heard.

5. CONCLUSIONSIn this study, the preferred soundscape composed of eight natural sounds, in a highly road traffic
noise polluted urban park, was assessed in an interactive way in VR and AR. The results show that theoptimized soundscapes mainly contain bird sounds in both the real and virtual representation of thepark. Additionally adding natural sounds improves the overall appreciation of the sound environment
in the park, and strongly enhances road traffic noise masking.

ACKNOWLEDGEMENTS
This research was part of C3PLACES (“Using ICT for co-creation of inclusive public spaces”), andreceived funding from the European Union’s Horizon 2020 research and innovation programme(Urban Europe) under grant agreement No 693443.

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