Loudness and distance estimates for noise bursts coming from several
distances with and without visual cues to their source
Gauthier BERTHOMIEU(1) , Vincent KOEHL(1) , Mathieu PAQUIER(1)(1) Lab-STICC, University of Brest, France, gauthier.berthomieu@univ-brest.fr

Abstract
The at-ear sound pressure decreases with the distance to the source. Since pressure plays an essential part inloudness judgments, loudness could be expected to decrease similarly with the distance to the source. Yet,several studies reported conflicting results when assessing loudness as a function of sound source distance. The
present study gathers loudness judgments for noise bursts displayed from several distances from listeners in a
virtual environment. A visual representation of the distant sound sources could or could not be available to thelisteners in order to modify the perceived distance of these sounds since visual distance cues affect auditory
distance perception. Sounds were displayed in free or diffuse fields in order to also provide auditory distancecues. The results of this study show that visual cues had no significant effect on loudness estimates, even though
they significantly affected apparent source distance judgments. The discrepancy between these results and thegenerally accepted loudness constancy phenomenon could come from the instructions that were given to thelisteners, which focused on “at-ear” loudness judgments whereas loudness constancy is predominantly obtained
when asking the listeners to make loudness judgments based on the sound source power.
Keywords: Loudness, Distance, Audiovisual interactions

1

INTRODUCTION

In everyday life, humans combine information from their different senses to apprehend the world in which
they live. In auditory research, audiovisual interactions are widely investigated as they underlie many phenomena. Earlier studies assumed that visual information could significantly affect perceived loudness [12, 3, 2] andauditory localization [5]. Besides, loudness perception is also known to depend on auditory localization [16].
The present study focuses on audiovisual interactions in conditions where a sound source is located at several
distances from a listener. When a sound is emitted, it propagates in the environment and its intensity lowers as
it gets farther from its source. Thus, the apparent loudness of this sound could be expected to decrease with the
distance between the source and the listener. However, a loudness constancy phenomenon tends to demonstratethat loudness estimates can, in certain conditions, be independent of source distance [10, 21]. This phenomenon
was assumed to rely on auditory cues to the source power (such as the reverberant energy) rather than on theperceived source distance [21]. Yet, visual cues to distance were also reported to modify loudness estimatesin conditions where auditory cues were fixed [9]. Then, it is unclear to what extent perceived loudness varies
with sound source distance and visual information to the source. Moreover, determining such relations can bedifficult because of the experimental design. Indeed, it can be complicated to easily manipulate a sound source
distance while controlling the visual and auditory information provided to a listener in the real world. Then, thepresent experiment was set up in a virtual environment, which allows to control sound source distance, auditory
and visual cues independently. This was carried out in order to observe the effects of visual information on theperceived loudness and distance of noise bursts displayed at several distances from a listener.

2

MATERIAL AND METHOD

A virtual environment was created in order to allow the experimenters to manipulate source distance, source
level, source visibility and room acoustics independently while providing the participants with a natural listen-3897

ing situation. During the experiment, listeners were seated on a chair and wore a HTC Vive virtual reality
head mounted display (HMD) displaying a virtual visual environment. A loudspeaker and a large panel weredisplayed in this environment. The listener faced the loudspeaker, which could be fully obstructed by the panel
if the latter was placed between the listener and the loudspeaker. A picture of the virtual environment is given
in Fig. 1.

Figure 1. Representation of the virtual visual environment gathering the loudspeaker, the panel, and traffic
cones. The green square depicts the listener’s position in the virtual environment, whose point of view faced
the loudspeaker. The red path represents the possible positions of the loudspeaker and the blue path those of
the panel. The ground texture is patterned with 1 m2 squares.

2.1 Auditory stimuli
Three room acoustics were studied: one anechoic, one from a large sports hall and one from a small concert
hall. For creating the auditory stimuli used in the two reverberant rooms, sine sweeps were first displayed by
a Genelec 8040A loudspeaker and recorded using a mh acoustics Eigenmike ambisonics microphone in a large
sports hall (RT60 = 2 s) and in a small concert hall (RT60 = 0.5 s). Sweeps were recorded at a unique microphone
position while the loudspeaker was at a distance of 1, 2, 4, 8 and 16 m. Fig. 2 is a drawing of both rooms that
includes a representation of the loudspeaker and microphone positions during the recordings.
44.3 m

4m

8m
1.5

m

18 m

14 m

19.4 m24 m
15.75 m

15.3

a.

m

b.

Figure 2. Drawings (to scale) of the large sports hall (a.) and small concert hall (b.) in which the recordings
were made. Filled circles depict the microphone positions, empty circles depict the loudspeaker positions.
Fourth order ambisonics Room Impulse Responses (RIRs) were computed from these recordings. The final
stimuli were obtained by convolving 200 ms white noise bursts with these RIRs for the two reverberant rooms

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and with anechoic RIRs for the anechoic room.
In order to provide a realistic listening situation while reproducing the sounds over headphones, the yaw, pitch
and roll values of the HMD were used to rotate the ambisonics field according to the movements of the subject’s
head thanks to the ambiX Rotator plugin [7]. Finally, ambisonics signals were converted to binaural sounds
using the IEM BinauralDecoder plugin1 .
Virtual sound sources could display noise bursts at three different levels so that at-ear pressure level did not rely
only on the sound source distance. These levels were fixed at 0, −6 and −12 dB with respect to a reference
level. This reference source level was adjusted so that the sound pressure level reached 80 dB SPL at the
subject’s ears when the source was located at 1 m from the listener.
45 stimuli were created this way, corresponding to the 3 source levels located at each of the 5 distances in eachof the 3 rooms.
The sounds were displayed over open circum-aural headphones (Sennheiser HD 650) after the use of headphonecompensation filters as provided by the IEM BinauralDecoder plugin1 . The sounds were played in MAXMSPand were delivered to the headphones by a RME Babyface Pro sound card. Restitution levels were calibratedusing a Brüel & Kjær sound calibrator Type 4231 and a Neumann KU 100 dummy head.
2.2 Visual stimuli
In their 2013 review of studies focusing on egocentric distance perception in virtual environments, Renner et
al. [15] concluded with a list of elements that are likely to improve the quality of distance perception in
virtual environments. They reported that “to facilitate distance perception as well as possible, it is important toprovide binocular disparity, use high quality of graphics, carefully adjust the virtual camera settings, display a richvirtual environment containing a regularly structured ground texture, and enhance the user’s sensation of presence”.
The visual environment of the present experiment was designed with regard to these recommendations. The
HMD provides the subjects with most pictorial (occlusion, relative size, height in the visual field and aerial
perspective) and non-pictorial (motion parallax, convergence and binocular disparity) visual distance cues. The
3D models were created and rendered in high quality then displayed on the 2160 × 1200 px screen of the HMD
at 90 frames per second. A structured ground texture was rendered and traffic cones were added to enrich thevirtual environment with constant size objects located at several distances. The head tracking provided by the
HMD, which is known to be a component of immersion and to enhance presence [15], was linked to the headtracking of the audio stimuli so that the consistency of information across modalities was preserved, which isalso an important factor for the sensation of presence [4].
Three different-sized environments were created, corresponding to the three rooms in which sounds were rendered. For the two reverberant rooms, the virtual environments were rooms that had the exact same dimensions
and shapes as the actual rooms in which the recordings were made (see Fig. 2). For the anechoic room, nowall was represented and the environment was an infinite regularly-structured ground texture. This was achievedsince the visual impression of the room enclosing the sound source is known to affect externalization [18] andcould therefore also improve the sensation of presence.
2.3 Procedure
The experiment took place in a small, acoustically-isolated audiometric room. Participants sat in a chair which
faced a tablet computer displaying a response interface that they could see in the virtual environment. The
experiment was split in two sessions, each corresponding to one task that was either to estimate the egocentric
source distance or to estimate the apparent loudness of the sounds it displayed.
Each session was then split in three sub-sessions corresponding to each room. In each of these sub-sessions, allcombinations of distance, sound source level and visibility of the loudspeaker were presented to each subject
four times in a random order. This led to a total of 120 estimates (5 distances × 3 source levels × 2 visibility
1 Plug-in description and download available at https://plugins.iem.at3899

conditions of the loudspeaker × 4 repetitions) per subject in each sub-session. See table 1 for a summary offactors levels and sessions. Apparent loudness was reported using a free-modulus magnitude estimation protocol[8] and apparent distance was reported in meters.
Table 1. Summary of the experimental conditions for each subject.
FactorTask (session)
Room (sub-session)
Distance
Source level
Loudspeaker
Repetition

LevelsLoudness estimate · Distance estimate
Anechoic · Concert hall · Sports hall
1 m · 2 m · 4 m · 8 m · 16 m
0 dB · −6 dB · −12 dB
Visible · Hidden
1 · 2 · 3 · 4

After each answer, the panel hid the loudspeaker while the loudspeaker moved to its position for the next trial.
Then, the panel revealed or not the loudspeaker (according to whether the loudspeaker had to be visible orhidden in the trial to come), the sound was played and the participants could type their answer. If in thecurrent trial the loudspeaker was hidden, the panel stayed in its position while the loudspeaker moved to its
next position so that the hidden loudspeaker position was not revealed2 .
Twenty subjects (5 women and 15 men aged 20 to 25 years) with normal hearing attended the experiment andwere remunerated for their participation. Instructions were given in written form within the virtual environment
and were also read by the experimenter at the beginning of each session (loudness or distance). Participants
carried out the two sessions on two different weeks and performed around ten training estimates at the beginningof each sub-session which answers were not kept. Half of the subjects began with the distance estimate session
and the other half with the loudness estimate session. Each session lasted approximately one hour.

3

RESULTS

Repeated-measures analyses of variance (ANOVA) were carried out to assess the factors effects and interactions
on loudness and distance estimates. Four factors were included in each of the two analyses: the room (3 levels),
the source distance (5 levels), the source level (3 levels) and the visibility of the source (2 levels). As this paper
focuses on the effect of the visibility of the sound source on the perceived distance and loudness, only effects
and interactions involving this factor will be analyzed and discussed. The results of these ANOVAs are given
Table 2.
3.1 Loudness estimates
Since loudness estimates were gathered using a free-modulus scale, they were first normalized using the same
method as described by Altmann et al. [1]. During this process, estimates were converted to their logarithm
which were normally distributed around the mean estimates. An ANOVA was performed on the normalized
logarithm of the loudness estimates. As indicated by the results given in the right side of Table 2, visibility did
not prove to have any significant effect on loudness estimates as well as no significant interaction with any otherfactor. The geometric means of the results are plotted in Fig. 3, which shows in each room (separated plots)
the geometric mean of loudness estimates made when the loudspeaker was either visible (solid lines) or hidden(dashed lines). Each plot gathers three lines of each type (solid and dashed), corresponding to the three source
levels (which is identified next to each line). This figure clearly shows that apparent loudness estimates weresimilar whether the loudspeaker was visible (solid lines) or hidden (dashed lines) in each of the experimental
configurations and that loudness constancy did not occur in any of these configurations.
2 Link to a video recording of the experiment: https://youtu.be/V1ifR558VO4

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Table 2. Results of the two ANOVAs. The left-side of the table shows the results of the ANOVA performed on
the logarithm of the distance estimates. The right-side of the table shows the results of the ANOVA performedon the logarithm of the loudness estimates. None of the interactions involving three or more factors was foundto be significant by one of the ANOVAs. Those interactions were therefore not displayed as a matter of clarity.
Dependent variable

Distance estimates

SourceRoomDistance
Level
Visibility
Room × Distance
Room × Level
Distance × Level
Room × Visibility
Distance × Visibility
Level × Visibility

Loudness estimates

SS

DF

MS

F

Sig.p

SS

DF

MS

F

Sig.p

9.165
163.111
16.564
.170
.693
.807
1.799
.294
1.531
1.476

1.132*

8.097
143.526
14.002
.170
.286
.390
.702
.214
.951
1.373

14.601
244.122235.614
3.543
3.948
11.13021.4647.659
13.73614.996.001< .001< .001.075.020< .001< .001.006< .001.001

1.783
36.35324.763
.017
2.059
.055
.269
.004
.014
.009

2
1.125*
1.042*
1
2.883*
2.451*
4.077*
2
2.363*
2.892
32.31623.759
.017
.714
.022
.066
.002
.006
.004

9.879
186.970217.213
2.125
37.202
1.492
5.960
.528
.712
1.230

< .001< .001< .001.161< .001.233< .001
.594
.518
.304

1.136*
1.183*
1
2.423*
2.070*
2.562*
1.374*
1.610*
1.075** A Greenhouse-Geisser correction was applied to the degree of freedom due to a sphericity assumption violation.

Visible source
Hidden source

Loudness estimate

0 dB

0 dB

10 1

0 dB
-6 dB

-6 dB

-6 dB

-12 dB-12 dB-12 dB

1

2

4

8

16

1

2

4

8

16

1

2

4

8

16

Figure 3. Geometric means of loudness estimates, with 95% confidence intervals. Means and limits of the confidence intervals were computed on the logarithm of the estimates and converted back to the original estimates.
3.2 Distance estimates
As distance estimates are approximately normally distributed along a logarithmic scale [20], each individual
distance estimate was converted to its logarithm prior to the analysis. The arithmetic mean of the four repetitionsof each trial was then computed for each participant and each trial. A repeated-measures analysis of variance
was conducted on these converted results. Results of this ANOVA are given in the left side of Table 2.
Visibility did not prove to have a significant simple effect on distance estimates, similarly to loudness, but
significantly interacted with the three other factors (level, distance and room), contrarily to loudness.
The significant “Level × Visibility” interaction shows that sound source level did not have the same effect on
distance estimates whether the loudspeaker was hidden or visible. A Bonferroni post hoc test revealed significant

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differences across source visibility conditions at the source levels −12 dB (p = .046) and 0 dB (p = .002). As
a result (see Fig. 4 a.), the distance estimate as a function of source level has a smoother slope when the
loudspeaker was visible (solid line) compared to when the loudspeaker was hidden (dashed line).
The significant “Distance × Visibility” interaction indicated that the distance estimates depended on the distanceitself and on the visibility of the loudspeaker. Bonferroni post hoc tests revealed a significant difference between
the two distances reported with or without visible loudspeaker when the latter was located at 1 m (p = .015),
8 m (p = .025) and 16 m (p = .001). For the closest distance (1 m), the estimated distance was closer when thesource was visible than when it was hidden whereas the contrary was observed at the two farthest distances.
This is shown in Fig. 4 b., where the averaged distance estimates made when the loudspeaker was either visible(solid line) or hidden (dashed line) are represented together with the actual distance of the loudspeaker.
The significant “Room × Visibility” interaction indicated that the distance estimates depended on the room andon the visibility of the loudspeaker. Bonferroni post hoc tests revealed a significant difference between the two
distances reported with or without visible loudspeaker in the anechoic room (p = .042) only, as it can be seenin Fig. 4 c., which represents the averaged distance estimates in each of the three rooms when the loudspeaker
was either visible (solid line) or hidden (dashed line).

6
Visible Source
Hidden Source
Actual distance

Visible Source
Hidden Source
Distance estimate (m)58Visible Source
Hidden Source

5

4

4
4

3

2
3

1
-12

a.

-6

0

1

source level (dB)

b.

2

4

8

16

Anechoic Concert hall Sports hallc.

Figure 4. Geometric means of distance estimates as a function of Level (a.), Distance (b.) and Room (c.) for
the two visibility conditions with 95% confidence intervals, computed in the same way as in Fig. 3.

4

DISCUSSION

The results of this study state that the loudness estimates were the same whether the loudspeaker was visibleor hidden, even though this was not the case for distance estimates.
According to the statistical analysis of the distance estimates, the “Level × Visibility” interaction was significant, and distance estimates were found to be less dependent on the source level (and then on the at-ear SPL)
when the source was visible than when it was hidden. This occurred not only in the anechoic room (wherevisual cues were the only absolute distance cues available) but also in the two reverberant rooms, which supports the prevalence of visual cues over auditory cues in distance estimates. Then, one could wonder if thesound source level still had an effect on distance estimates when the source was visible. A Bonferroni post hoc

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test revealed that this was still the case, as distance estimates were significantly different between source levels(0 dB vs. −6 dB (p < .001), −6 dB vs. −12 dB (p < .001)) even when the source was visible.
The significant “Distance × Visibility” interaction revealed that seeing the loudspeaker led to closer distanceestimates when the loudspeaker was close to the participants and to farther estimates when the loudspeaker was
distant. Since distance estimates are often overestimated for close sources and underestimated for remote sourcesin auditory and not in visual depth perception [6], this interaction proves an improvement of distance estimateswhen visual cues were available, as it can be seen in Fig. 4 b. where the averaged distance estimates madewhen the loudspeaker was visible (solid line) are closer to the actual distances (dotted line) than the averaged
distance estimates made when the loudspeaker was hidden (dashed line).
The significant “Room × Visibility” interaction and its post hoc test indicated that the distance perception
depended on the visual cues only if they were the only available distance cues. In the reverberant rooms, thediffuse field and visual cues appeared to provide the participants with similar information about distance.
Despite the effective modification of perceived distance achieved by providing the participants with visual cues
to the sound source distance, no significant effect of the visibility of the loudspeaker was found on the loudness
estimates in any experimental condition. These findings are in accordance with previous studies that found noloudness constancy with the distance of non-familiar sound sources when asking the participants to base their
judgment on the loudness “at the ear” [17, 13, 1], as opposite to judgments based on the loudness “at thesource”, which are more likely to show loudness constancy [10, 21]. However, loudness constancy had been
observed when asking participants to report apparent loudness estimates for speech [14, 19]. This might be dueto the particularities of speech, which contains intrinsic information about its source power (a whisper is known
to be less powerful than a shout), and which involves a specific perception [11]. Then, one could wonder if
apparent loudness perception relies on the source power perception. In the current study, direct information
about the source power was available in the reverberant rooms through the reverberant energy, which was not
the case in the anechoic room. However, the “Room × Level” interaction did not have a significant effecton loudness estimates. This means that apparent loudness was the same whether information about the soundsource power was available or not.

5

CONCLUSIONS

The results of the present experiment show no interaction between visual information and “at the ear” loudness
estimates for white noise bursts displayed by a loudspeaker in anechoic or reverberant virtual environments, eventhough distance estimates depended significantly on visual information. These findings support the hypothesis
that, contrarily to speech, information about the source level has no effect on “at the ear” loudness estimates fornoise. Further experiments will be carried out following this hypothesis, which will investigate “at the source”
loudness estimates for noise and both loudness estimates for speech in the environments of the present study.

ACKNOWLEDGEMENTS
The authors wish to thank the IRT b<>com, the staff of the “Image & Son” department of the University of
Brest and everyone who participated in this experiment.

REFERENCES[1] C. F. Altmann, M. Matsuhashi, M. Votinov, K. Goto, T. Mima, and H. Fukuyama. Visual distance cues
modulate neuromagnetic auditory N1m responses. Clin. Neurophysiol., 123(11):2273–2280, 2012.
[2] G. Berthomieu, V. Koehl, and M. Paquier. Directional loudness of low-frequency noises actually presented
over loudspeakers and virtually presented over headphones. J. Audio Eng. Soc., in press.
[3] H. Fastl and M. Florentine. Loudness in daily environments. In Loudness, pages 199–221. Springer, 2011.

3903

[4] R. M. Held and N. I. Durlach. Telepresence. Presence: Teleoperators Virtual Environ., 1(1):109–112, 1992.
[5] E. Hendrickx, M. Paquier, V. Koehl, and J. Palacino. Ventriloquism effect with sound stimuli varying inboth azimuth and elevation. J. Acoust. Soc. Am., 138(6):3686–3697, 2015.
[6] A. J. Kolarik, B. C. J. Moore, P. Zahorik, S. Cirstea, and S. Pardhan. Auditory distance perception
in humans: a review of cues, development, neuronal bases, and effects of sensory loss. Atten Percept
Psychophys, 78(2):373–395, 2016.
[7] M. Kronlachner. Plug-in Suite for mastering the production and playback in surround sound and ambisonics. In Proceedings of the 136th AES convention, Berlin, Germany, 2014.
[8] L. E. Marks and M. Florentine. Measurement of loudness, part I: Methods, problems, and pitfalls. In
Loudness, pages 17–56. Springer, 2011.
[9] D. H. Mershon, D. H. Desaulniers, S. A. Kiefer, T. L. Amerson, and J. T. Mills. Perceived loudness andvisually-determined auditory distance. Perception, 10(5):531–543, 1981.
[10] K. Mohrmann. Lautheitskonstanz im entfernungswechsel. Zeitschrift f. Psychol., 145:145–199, 1939.
[11] B. C. J. Moore. Speech perception. In An introduction to the psychology of hearing, pages 299–332. BRILL,
Leiden, Netherlands, 2012.
[12] E. C. Odgaard, Y. Arieh, and L. E. Marks. Brighter noise: Sensory enhancement of perceived loudness byconcurrent visual stimulation. Cogn. Affect. Behav. Neurosci., 4(2):127–132, 2004.
[13] J. Petersen. Estimation of loudness and apparent distance of pure tones in a free field. Acta Acust. unitedAc., 70:5, 1990.
[14] I. Pollack. On the measurement of the loudness of speech. J. Acoust. Soc. Am., 24(3):323–324, 1952.
[15] R. S. Renner, B. M. Velichkovsky, and J. R. Helmert. The perception of egocentric distances in virtualenvironments - A review. ACM Computing Surveys, 46(2):1–40, 2013.
[16] V. P. Sivonen and W. Ellermeier. Directional loudness in an anechoic sound field, head-related transfer
functions, and binaural summation. J. Acoust. Soc. Am., 119(5):2965–2980, 2006.
[17] S. S. Stevens and M. Guirao.
34(9B):1466–1471, 1962.

Loudness, reciprocality, and partition scales.

J. Acoust. Soc. Am.,[18] J. Udesen, T. Piechowiak, and F. Gran. The effect of vision on psychoacoustic testing with headphonebased virtual sound. J. Audio Eng. Soc., 63(7/8):552–561, 2015.
[19] R. M. Warren, E. A. Sersen, and E. B. Pores. A basis for loudness-judgments. Am. J. Psychol., 71(4):700,
1958.
[20] P. Zahorik. Auditory distance perception in humans: A summary of past and present research. Acta Acust.
united Ac., 91:12, 2005.
[21] P. Zahorik and F. L. Wightman. Loudness constancy with varying sound source distance. Nat. Neurosci.,
4(1):78–83, 2001.

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