PROCEEDINGS of the
23rd International Congress on Acoustics
9 to 13 September 2019 in Aachen, Germany

Soundscape reproduction using headphones for web-based
listening test
Anugrah Sabdono SUDARSONO1; Joko SARWONO1
1

Kelompok Keahlian Fisika Bangunan Institut Teknologi Bandung, Indonesia

ABSTRACTOne of the methods to analyse a soundscape is by reproducing the acoustic environment. The acoustic
environment reproduction usually conducted using multi-speaker systems in a laboratory. The experimentusually conducted individually resulting limited respondent of the experiment. A web-based experiment is
one of the alternatives to do the soundscape study. By using the internet, the experiment can be done easierwith more respondents.
The experiment using the internet usually conducted using an online questionnaire which can play a stereo
sound or a video. In this study we are testing the validity of XY, Mid-Side, and Head Tracking decoders to
reproduce acoustic environments using headphones. The XY and Mid-Side decoders were used to decode
B-Format signals to stereo signal which can be played directly by the online questionnaire. The head tracking
system is used to represent the experiment conducted using Youtube 360 of Facebook 360.
Analysis based on semantic score indicates that the listening test conducted using stereo decoders can gives
the similar score with the listening test conducted using ambisonic reproduction system. Further analysis
using semantic differential analysis shows that the experiment conducted using Mid-Side decoders candeliver the same soundscape dimensions with the in-situ experiment.
Keywords: Soundscape Reproduction, Headphones, Internet, Stereo Decoder

1. INTRODUCTION
Soundscape analysis is conducted using three methods: in-situ experiment, laboratory experimentand recalled in memory (1). The in situ experiment gives the best result in term of the validity of theexperiment although it has the problem in the repeatability of the research (2).
The laboratory experiment has become another alternative for soundscape experiment. It usuallyconducted in three methods: by reproducing the acoustic environment (3), by simulating the acoustic
environment (4,5), and by composing the acoustic environment (6,7). Those three methods implement
ambisonic reproduction system to reproduce the sound in the lab.
Soundscape experiment using soundscape reproduction has been validated using semantic
categorisation (8,9) and semantic differential analysis (3,10). The reproduction system verified bycomparing the response in the laboratory condition to the original soundscape. Using semantic
categorisation, Guastavino et al. compare stereo reproduction, two-dimensional ambisonic system andthree-dimensional ambisonic system and suggest that the two dimensional ambisonic system issuitable for acoustic environment reproduction (8).
Another study also compares the soundscape dimension from ambisonic reproduction system.
Davies et al. reproduce urban acoustic environment using three dimensional ambisonic (10) resulting
the same dimension from Kang’s experiment(11): Relaxation, Dynamic, Communication, and Space.
Sudarsono et al. use the same method to compare the soundscape dimension in situ and in thelaboratory experiment using two-dimensional ambisonic system resulting three soundscape dimension,
which is consistent on both of the experiment: Relaxation, Dynamic, and Communication (12).
The laboratory experiment has an advantage in the repeatability of the experiment. However, since
the sonic environment needs to be reproduced using the many speakers, a room with acoustic treatment
is needed to build the system. The experiment must also be conducted individually in the room where
the system is installed.
Another alternative of conducting soundscape research is by using headphones (13–16). The study
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anugrah@tf.itb.ac.idusing headphones has some advantages: the experiment can be conducted everywhere, theparticipation of the study can get higher than the laboratory experiment, and the system set up issimpler than the experiment using ambisonic reproduction system. Furthermore, the soundscapeexperiment using headphone open the possibility to do the experiment using the internet using online
questionnaire (17).
There are two ways to reproduce the acoustic environment by the interne t: stereo reproduction, andvirtual reality. The stereo reproduction is a common method to reproduce sound in an online
questionnaire and the virtual reality reproduction can be done using Youtube 360 or Facebook 360.
In this study, comparison between XY, Mid-Side, and Head Tracking is done in order to understandwhich decoders are suitable to do web-based listening test using headphone. The XY and Mid-Side
decoders are used to decode B-Format signals to stereo signal which can be played directly by the
online questionnaire. The head tracking system is used to represent the experiment conducted using
Youtube 360 of Facebook 360.

2. METHODS
2.1 Acoustic Environment Recording
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Four acoustic environment recordings were recorded in a stationary position using Soundfield
ST-250 microphone and Roland R-44 digital recorder in Manchester city centre area. The entire
acoustic environment is recorded in B-Format which consist of four outputs (W, X, Y, and Z). The
location and description of the recording used in the experiment are shown in Table 1.
Table 1-Description of recording's locations
LocationsMarket Street

St Ann Square

Piccadilly Garden

Food Market at Piccadilly Garden

Descriptions
Outdoor shopping lane surrounded by two
floors shopping building; selected because thespace represents urban soundscape without
traffic noise.
Pedestrianized square; away from traffic;
mixed-use building around the space; twonatural sound objects appear: water fountainand birds chirping; selected because this space
has natural sound objects
Open public space; main bus and tram stops;
selected because the space represents urban
soundscape with traffic noise;Open public space; main bus and tram stops;
busy food market; selected because in thisspace, the traffic noise is masked by the soundof hubbub.

Dominant Sound Sources
Hubbub and live music

Water fountainLive music, hubbub, and trafficnoise
Hubbub, live music, and trafficnoise

2.2 Experiment
The experiment was conducted to analyse the soundscape reproduced by a different decoder s,
which could be implemented in web-based listening test. Three decoders were used in this experiment:
Mid-Side decoder, XY decoder and head tracking decoder. The Mid-Side decoder used in this study is
the Voxengo MSED VST Plug-in (18), the XY decoder used in this study is Soundfield SurroundZone2
VST Plug-in(19), and the head tracking decoder used Nx Ambisonic head tracker system from Waves(20). The sound level of reproduction is calibrated to the level 9.5 dB lower than the actual sound level.

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Figure2 -Signal Decoding implemented in the experiment
The experiment was conducted using AKG K550 headphones in a quiet room. Fifteen participants(eight males and seven females, average age: 24.8, SD: 5.3) joined the experiment voluntarily. The
entire participants were bachelor, master, and post-graduate students of Engineering Physics
Department of Institut Teknologi Bandung. The experiment was conducted individually and last for
about 45 minutes.
The entire participant listened to four recordings (decoded using three decoders) through theheadphones and requested to fill the semantic scales made by Microsoft Excel as shown in Figure 3.

Figure 3-The interface of questionnaire
The semantic scales are the scale used in the previous study about the validation of soundscape
reproduction using ambisonic reproduction system (12). The scale was developed based on the study
conducted by Kang et al. (21).
The calibration of the reproduction system was done using Dummy Head GRAS 45BB KEMAR
Head and Torso to the level that represents -9.5 dB below the actual level. The calibration concept isbased on the previous study about the effect of the sound level ad justment to the perception of theacoustic environment reproduction (12). This method has been validated in the previous study (22)

3. ANALYSISThe effect of stereo decoder variation to the soundscape is analysed using two methods: scorecomparison and principal component analysis. The result of this study then compared to the previous
experiment result using two-dimensional ambisonic system (12).
The first score is analysed using Analysis of Variance (ANOVA) between the score of semantic
scales from four recordings reproduced using three stereo decoders. ANOVA shows that the difference
between three stereo decoders (XY, Mid-Side, and Head Tracking) in general are not significant. Only
the score of the scale of quiet from Piccadilly Garden (sig. 0.024), the scale of hard from Food Market(sig. 0.011) and the scale of directional from Food Market (sig. 0.032) indicate significant difference
due to the stereo decoder variation.

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Further analysis is conducted by comparing the average value of the perception according to thedecoder variation with the result from the perception of the same acoustic environment reproduced by
two-dimensional ambisonic reproduction. The mean comparison is shown in Figure 4. In general, theperception of the headphones reproduction and ambisonic reproduction is similar.

Market Street
XY

Mid-Side

St Ann Square

Track

Ambisonic

Comfort
4,00
Directional
Quiet
Far
Pleasant
2,00
Reverberant
Natural0,00
Varied

-2,00

Like

Sharp

-4,00

GentleFast

BoringHard
SmoothCalming

Mid-Side

Track

Ambisonic

Comfort
4,00
Directional
Quiet
Far 2,00
Pleasant
Reverberant

0,00

NaturalVaried

-2,00

Like

Sharp

-4,00

GentleFast

BoringHard
SmoothCalming

SocialCommunal
Meaningfull

Mid-Side

Track

Ambisonic

Comfort
3,00
Directional
Quiet
Far 2,00
Pleasant
1,00
Reverberant
Natural0,00-1,00
Varied
Like
-2,00
-3,00
Sharp
GentleFast

BoringHard
SmoothCalming

SocialCommunal
Meaningfull

Piccadilly Garden
XY

XY

SocialCommunal
Meaningfull

Food Market at Piccadilly
GardenXY

Mid-Side

Track

Ambisonic

Comfort
4,00
Directional
Quiet
Far 2,00
Pleasant
Reverberant
Natural0,00
Varied
Like
-2,00
Sharp

-4,00

GentleFast
Hard
SmoothCalmingBoringSocialCommunal
Meaningfull

Figure 4-The average rating of soundscape dimension for different decoders
The semantic differential analysis is implemented to analyse the soundscape dimensions from thesonic environment recording. The Principal Component Analysis (PCA) from XY decoder experimentshows three reliable (Cronbach Alpha > 0.7) soundscape dimensions as shown in Table 2:x The dimension related to the perception of dynamic and communication (33%). The dimension
is represented by the semantic scale of Quiet, Gentle, Social, Communal, Calming, Smooth,Hard, Fast, Sharp, Varied, and Far.
x The dimension related to the perception of relaxation (21%). The dimension is represented by
the semantic scale of Comfort, Pleasant, Natural, Like, Gentle, Calming.
x The dimension related to the perception of meaningful (10%). The dimension is represented by
the semantic scale of Boring, and Meaningful.
The soundscape dimensions from the experiment using XY decoders shows a different result fromthe in-situ experiment and the laboratory experiment using ambisonic system (3). The in-situ
experiment shows three reliable soundscape dimensions: Relaxation (24%), Dynamic (14%), andCommunication (11%). The laboratory experiment using the ambisonic system also shows three6117

reliable soundscape dimensions: Relaxation (32%), Dynamic (18%), and Communication (12%).
The first dimension in the experiment using XY decoder is a combination of the dimension of
dynamic and communication in the in-situ experiment. This dimension also represents the perception
related to the sound object. The result indicates that the participant mainly relates the perception to
the sound reproduced by the headphones and not the emotional aspect.
The experiment using the XY decoder shows that although the ANOVA shows the variation ofdifferent headphones is not affecting the perception much, the PCA shows different soundscapedimension. This result indicates that people react differently compared to the in -situ condition.
Table 2-Principal Component Analysis result of XY, Mid-Side, and Head Tracking Decoders
Component
33%

21%

10%

7%

34%

13%

12%

8%

PCA XY Decoder (N= 84, KMO index 0.762,

PCA Mid-Side Decoder (N= 84, KMO index 0.781,

Bartlett’s test of sphericity sig. 0.000)

Bartlett’s test of sphericity sig. 0.000)

Comfort
Quiet

.794
-.764

Comfort

.830

Quiet

.736
.847

Pleasant.847

Pleasant

Natural.680

Natural

Like

.869

Like

.869

.533

Gentle.873

Gentle-.610

Boring-.875

Boring

-.610

.815

Social.771

Communal.828

Communal

.756

.832

Calming-.573

SmoothMeaningfull

.691

.632

Calming

.797

-.737

Smooth

.779

Hard

.761

Hard

-.757

Fast

.723

Fast

.525

Sharp

.755

Sharp

.661

Varied.758

VariedReverberant
Far

.752
-.672

Cronbach's Alpha

0.93

.545

Reverberant

.902

Far

Directional
0.91

0.75

.668

Directional

0.28

Cronbach's Alpha

7%

-.716

SocialMeaningful

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Component

-.817
-.506
0.94

0.73

0.83

0.22

0.29

Component
23%

21%

15%

9%

8%

PCA Head Tracking Decoder (N= 84, KMO index 0.718,
Bartlett’s test of sphericity sig. 0.000)
Comfort
Quiet

.819
-.591

.552

Pleasant.829

Natural

.703

Like

.855

Gentle.761

Boring-.530

Social.651

Communal.649

Meaningful.756

Calming.572

Smooth

.831

Hard

.604

Fast

.702

Sharp

.868

Varied

.896

-.566

Reverberant

.668

Far

-.701

Directional.847

Cronbach's Alpha

0.88

0.88

0.86

0.57

0.38

The PCA from the experiment using Mid-Side decoder shows three reliable (Cronbach’s
Alpha>0.7) soundscape dimensions as shown in Table 2:x The dimension related to the perception of relaxation (34%). The dimension is represented bysemantic scale of Comfort, Quiet, Pleasant, Like, Gentle, Calming, Smooth, Hard.
x The dimension related to the perception of dynamic (13%). The dimension is represented bysemantic scale of Boring, Fast, Sharp, and Far.
x The dimension related to the perception of communication (12%). The dim ension isrepresented by the semantic scale of Social, Communal, and Varied.
The soundscape dimension from the experiment using Mid-Side Decoder shows the similarsoundscape dimension to the in-situ and the laboratory experiment using ambisonic system:
Relaxation, Dynamic, and Communication. Furthermore, the order of the dimension also consistent
with the in situ and the validated laboratory experiment.
The dimension of Relaxation in this experiment shows the similar variance to the laboratory
experiment using ambisonic system (38% in the validated laboratory experiment and 34% in our
experiment. The dimension of dynamic variance shows 5% difference in the variance of the validated
laboratory experiment. The dimension of communication shows the same variance to the dimension ofcommunication in the validated laboratory reproduction experiment.
The Mid-Side experiment shows that the reproduction system can reproduce the similar soundscapedimension to the in-situ condition and the validated laboratory experiment. This result shows that the
Mid-Side Reproduction system is adequate to be used in soundscape experiment.

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The experiment using head tracking decoder shows three reliable (Cronbach’s Alp ha > 0.7)
soundscape dimensions as shown in Table 2:x The dimension related to the perception of dynamic and communication (23%). The dimension
is represented by the semantic scale of Quiet, Boring, Social, Communal, Hard, Fast, Sharp,
and Varied.
x The dimension related to the perception of relaxation (21%). The dimension i s represented by
the semantic scale of Comfort, Quiet, Pleasant, Natural, Like, and Calming.
x The dimension related to the perception of smoothness (10%). The dimension is represented
by the semantic scale of Gentle, Smooth, and Hard.
The soundscape dimension from the experiment using head tracking decoder shows the similar
result to the experiment using XY decoder. The result shows different perception to the in -situ
experiment and the validated laboratory experiment. The result of this experiment is consistent withthe experiment using XY decoders, which are dominated by the perception related to the rating of thesound objects.
Many study regarding soundscape dimension’ study has determined several soundscape dimensions.
Although there is some soundscape dimensions difference, the first dimension always represents theemotional aspect: relaxation, pleasantness, calmness, and emotional assessment. The sonicenvironment reproduction using headphones and Mid-Side decoder shows the same characteristic withthe other soundscape dimension. Furthermore, the soundscape dimensions are consistent with thein-situ experiment conducted by Kang et al. (11) and Sudarsono et al. (3).

4. CONCLUSIONSThe study has compared three stereo decoders for soundscape reproduction using headphones: XY
decoder, Mid-Side Decoder and Head Tracking Decoder. This study shows that the Mid -Side decoderis suitable for soundscape reproduction based on the semantic scales score comparison to the validated
reproduction system. Furthermore, analysis using semantic differential analysis shows the same
soundscape dimensions with the in-situ experiment and the validated soundscape reproduction:
relaxation, dynamic, and communication. Hence, this result shows that the soundscape experimentusing headphones using Mid-Side Decoder can be a good alternative in soundscape study especiallythe experiment conducted using the internet.

ACKNOWLEDGEMENTS
This research is funded by Institut Teknologi Bandung

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