Impact of head movement on sound localization
with band-limited noise
Daisuke Morikawa1, Yuki Toyoda2, and Tatsuya Hirahara3
1-3

Toyama Prefectural University

5180 Kurokawa, Imizu, Toyama 939-0351 JAPANABSTRACTThis paper clarifies the relationship between head movement and sound localization with band-limited
noise (12-kHz high-pass, 500-Hz low-pass and 2-4-, 4-8-, 8-12-kHz band-pass filtered noise). 12-kHz
high-pass noise mainly provides interaural level difference (ILD) information, while 500-kHz low-passnoise mainly provides interaural time difference (ITD) information. Band-pass noises provide a mixture of
ILD and spectral cue information depending on the bandwidth. Four subjects listened to each band-limited
noise in head-still and head-movement conditions. Regarding horizontal plane, sound localization was
difficult in the head-still condition, while it was possible in the head-movement condition. These results
suggest that temporal variation of ITD and ILD caused by head movement impacts horizontal soundlocalization. Regarding the median plane, sound localization was also difficult in the head-still condition,
while it was sometime possible in the head-movement condition. However, improvement in soundlocalization performance varied from bandwidth to bandwidth of the stimuli. These results suggest that
temporal variation of the spectral cue caused by head movement impacts median sound localization.
Keywords: Sound localization, Signal bandwidth, Head movement

1. INTRODUCTION
Three-dimensional (3-D) sound can be reproduced by either binaural, transaural, wave-field
synthesis, or multi channel surround sound technology. It is known that the interaural time difference(ITD), interaural level difference (ILD), and spectral cues, which are involved in the head-relatedtransfer function (HRTF) or head-related impulse response, greatly contribute to 3-D soundlocalization [1]. There have been, however, few reports on how broad bandwidth is necessary toperceive reproduced sound as 3-D sound. Regarding the horizontal plane localization, Nakabayashi
reported that the signal bandwidth over 8 kHz is important [2]. In addition Arrabito et al. reported
that the signal bandwidth over 14 kHz is not necessary [3]. We have confirmed that signal bandwidthfrom 2 to 12 kHz is necessary and sufficient [4]. Regarding the median plane localization, Morimoto
et al. reported that the signal bandwidth from 4.8 to 9.6 kHz is necessary [5]; whereas, Hebrank et al.
reported that the signal bandwidth from 4 to 16 kHz is necessary [6]. All these values were obtainedin the head-still condition. However, it is known that head movement greatly impacts soundlocalization [7-11]. We clarify the impact of head movement on horizontal as well as median soundlocalization with high-pass, low-pass and band-pass noises which are difficult to localize in thehead-still condition.

2. EXPERIMENTAL SYSYEM
2.1 System
Figure 1 shows the experimental system. The system consisted of a Windows-based PC, three1

t074001@st.pu-toyama.ac.jp
t054013@st.pu-toyama.ac.jp
3hirahara@pu-toyama.ac.jp
21

8-channel digital-to-analog converters (DACs) (Roland, UA-101), 12 power amplifiers (BOSE,
1705II), and 17 loudspeakers (Vifa, MG10SD-09-08). The sampling frequency of the DACs was 48
kHz. The loudspeakers were placed around a chair in a horizontal and upper hemisphere in the
median of 1-m radius at 30-degree intervals. The height of these horizontal loudspeakers was 1.1 m.
The sound localization experiment was carried out in an experimental room with the walls andceiling covered with sound absorbing materials. The A-weighted sound pressure level of the roomwas 23 dB and reverberation time was less than 50 ms.
2.2 Stimuli
Broadband noise, i.e., Gaussian distributed random noise, high-pass (cut-off frequency: fc = 12kHz), low-pass (fc = 500 Hz) and band-pass (fc = 2-4, 4-8, 8-12 kHz) filtered noise were used as
stimuli. The high-, low-, and band-pass filters were 512-tap finite impulse response (FIR) filters with
60-dB stop-band attenuation. The stimulus duration and inter stimulus interval were both 3 s. A
30-ms linear taper window was applied at the beginning and end of the stimuli. As the frequency
responses of the loudspeakers are fairly flat (±8.7 dB) between 0.1 to 20 kHz, no inverse filter wasused to correct the speaker response in the experiment. The sound pressure level of the broadband
noise was 70 dB, while those of the high-pass, low-pass and band-pass filtered noises decreased
according to the filtering.
2.3 Procedure
The experimental procedure was as follows. Subjects sat on a chair placed in the center of the
speaker array and listened to stimuli reproduced from one of the loudspeakers. In the head-still
condition, subjects were instructed to close their eyes and keep their head still when a stimulus was
reproduced. In the head-movement condition, subjects were instructed to close their eyes and movetheir heads in a horizontal direction when a stimulus was reproduced.
Regarding the horizontal plane sound localization experiment, subjects were asked to localize thesound image position of real sound sources and to mark the localized angle from one of 12 directions
on an answer sheet. Each session consisted of 60 trials, and the stimuli were presented in random
order from the 12 loudspeakers. Regarding the median plane sound localization experiment, subjects
were asked to localize the sound image position of real sound sources and to speak the localized
angle from one of 7 directions on a microphone. Each session consisted of 35 trials, and the stimuli
were presented in random order from the 7 loud speakers. One experiment consisted of 4 sessions,
resulting in 20 answers from each direction. Experiments were conducted separately for eachbroadband, high-pass, low-pass and band-pass noise stimulus in the head-still and head-movement
conditions.

3300
Vifa
MG10 SD-09-08

USB
PC

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30°

1100

BOSE
RolandMODELEDIROL
UA-101 1705 II

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2.4 Subjects
Four normal-hearing males in their 20s, whose hearing thresholds had been measured,participated in the sound localization experiments.

DA

Figure 1 – Experimental system and setup

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30°
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1100
(height)

3. RESULTS

Broadband

HPN12 kHz

LPN500 Hz

BPN2-4 kHz

BPN4-8 kHz

BPN8-12 kHz

Head-movement

Head-still

360
300
240
180
120
60
0
360
300
240
180
120
60
0

0 120

240 360 0 120

240 360 0 120

240 360 0 120 240 360 0 120
Target Azimuth [ degrees ]240 360 0 120

240 360

Figure 2 – Horizontal sound localization results

Head-still condition

Head-movement condition

Improvement rate

100

100

80

80

60

60

40

40

20

20

0

Broadband

HPN12kHz

LPN500Hz

BPN2-4kHz BPN4-8kHz BPN8-12kHz

Figure 3 – Horizontal sound localization performance and improvement rate

30

Improvement rate [ % ]localization performance [ % ]Perceived Azimuth [ degrees ]3.1 Horizontal Sound Localization
Figure 2 is the pooled horizontal sound localization results for the four subjects for each stimulus.
The ordinate of each panel represents the perceived azimuth, and the abscissa, the target azimuth.
The size of each circle is proportional to the number of answers. The sound images were localized
away from the head for all stimuli. Regarding the head-still condition, localization was almost
perfect for broadband noise. However, sound localization was difficult with other stimuli. As seen in
the results of the 12-kHz high-pass noise, localization was vague. For the 500-Hz low-pass noise,many stimuli were localized with front-back confusion. From the results of the band-pass noises,
many stimuli were localized to neighboring angles and some stimuli were localized with front-backconfusion. Regarding the head-movement condition, localization was almost perfect with all stimuli.
Figure 3 plots the mean sound localization performance, i.e., the correct rate for localizing soundstimuli, and the improvement rate for the four subjects for each stimulus. Localization performancewas 96% for broadband noise in the head-still condition. In addition, localization performance waspoorer for the 12-kHz high-pass, 500-Hz low-pass, and band-pass noises than for broad band noise in
the head-still condition. Localization performance was 76, 69, 64, 69 and 70% for the 12-kHz
high-pass, 500-Hz low-pass, 2-4-, 4-8, and 8-12-kHz band-pass noises, respectively. In contrast,
localization performance was over 93% with each stimulus in the head-movement condition.
Localization performances improved 17 to 35% for band-limited noises due to head movement.

3.2 Median Sound Localization
Figure 4 is the pooled median sound localization results for the four subjects for each stimulus.
The sound images were localized away from the head for all stimuli. Regarding the head-still
condition, localization was difficult with all stimuli. From the results of the 12-kHz high-pass and8-12-kHz band-pass noises, localization was vague with stimuli from the front. However,
localization was very difficult with stimuli from the rear. For the 500-Hz low-pass noise, localization
was impossible with the stimuli. For the 2-4-kHz band-pass noise, localization was possible only
front or back. For the 4-8-kHz band-pass noise, localization was vague with the stimuli. Regarding
the head-movement condition, localization improved with all stimuli.
Figure 5 plots the mean localization performance and improvement rate for the four subjects foreach stimulus. Localization performance was 72, 40, 17, 28, 25% and 29% for the broadband,
12-kHz high-pass, 500-Hz low-pass, 2-4-, 4-8-, and 8-12-kHz band-pass noises. In contrast,
localization performance was 92, 71, 70, 55, 83 and 70% for the broadband, 12-kHz high-pass,
500-Hz low-pass, 2-4-, 4-8-, and 8-12-kHz band-pass noises. Localization performances improved
28 to 57% for the band-limited noises due to head movement. However, localization performance
was poorer, less than 15%, for the 2-4-kHz band-pass noise than for other stimuli.
HPN12 kHz

LPN500 Hz

BPN2-4 kHz

BPN4-8 kHz

BPN8-12 kHz
Head-still

120
60
0
180

Head-movement

Perceived Azimuth [ degrees ]Broadband
180

120
60
0
0

60 120 180

060 120 180

060 120 180 0 60 120 180
Target Azimuth [ degrees ]0

60 120 180

060 120 180

Figure 4 – Median sound localization results

Head-movement condition

Improvement rate

100

100

80

80

60

60

40

40

20

20

0

Broadband

HPN12kHz

LPN500Hz

BPN2-4kHz BPN4-8kHz BPN8-12kHz

Improvement rate [ % ]localization performance [ % ]Head-still condition

0

Figure 5 – Median sound localization performance and improvement rate

4. DISCUSSION
Figure 6 shows the frequency range of the acoustical cues, ITD, ILD, and spectral cues, to be
calculated. The ITD is calculated from the low-frequency component below 1.5 kHz [1]. The ILD ismainly calculated from the high-frequency component above 1.5 kHz [1]. The spectral cues are4

calculated from the middle-frequency component, from 5 to 10 kHz [1] or 6 to 16 kHz [12].
Therefore, the 500-Hz low-pass noise mainly provides ITD information, the 12-kHz high-pass noiseand band-pass noises provide a mixture of ILD and spectral cue information depending on its
bandwidth. It is known that ITD and ILD greatly contribute to horizontal plane localization. By
contrast, spectral cues are known to be important for median sound localization.
Regarding the horizontal sound localization, localization performance was poorer, 20% or more,
for the high-pass, low-pass and band-pass noises than the broadband noise in the head-still
conditions because the 500-Hz low-pass noise does not have frequency components to calculate ILD.
Therefore, a number of front-back confusions occurred with these stimuli. Likewise, the 12-kHz
high-pass and band-pass noises do not have frequency components to calculate ITD. Therefore, anumber of localization errors to neighboring angles occurred for these stimuli. By contrast, soundlocalization was quite possible in the head-movement condition for all stimuli. Front-backconfusions and miss localization to neighboring angles disappeared almost completely. These results
clearly show that the temporal variation of ITD and ILD caused by head movement has greatly
impacts horizontal sound localization.
Regarding the median sound localization, localizations were more difficult with all median planestimuli in the head-still condition because all stimuli have the same ITD and ILD (= 0). It is the only
spectral cue that can be used for localization. Thus, the bandwidth of the stimuli is important for
localization. Localization was very difficult with the 500-Hz low-pass noise because it lacks afrequency band for calculating the spectral cues. In contrast, localization was better than those of theother band-limited noises for stimuli presented from the front for the 12-kHz high-pass and8-12-kHz band-pass noises because they have enough frequency components to calculate ILD andspectral cues.
By contrast, sound localization was possible in the head-movement condition because ΔITD and
ΔILD can be caused by head movement. Sound localization was most difficult with the 2-4-kHz
band-pass noise in the head-movement condition. This is because it does not have frequency
components to calculate spectral cues compared with the stimuli in which both ΔILD and spectral
cues are available, or the 500-Hz low-pass noise in which ΔITD is only available. These results
clearly show that temporal variation of the ITD, ILD, and spectral cues caused by head movement
impacts in median sound localization.

BPN4-8kHz
HPN12kHz
BPN2-4kHz
BPN8-12kHz

LPN500Hz
ITD

ILD
Spectral cue
0.02 0.5

1

1.5 2
4
frequency [kHz]8

12 16 20

Figure 6 – Relationship between frequency components and localization information

5. CONCLUSION
Horizontal and median sound localization experiments for broadband, high-pass, low-pass, andband-pass noises were conducted with four subjects. The obtained results are as follows:(1) Horizontal sound localization performance was 96, 76, 69, 64, 67 and 70% for the broadband,
12-kHz high-pass, 500-Hz low-pass, 2-4-, 4-8-, and 8-12-kHz band-pass noises, respectively, inthe head-still condition.
(2) Horizontal sound localization was over 93% for all stimuli in the head-movement condition.
(3) Median sound localization performance was 72, 40, 17, 28, 25 and 29% for the broadband,
12-kHz high-pass, 500-Hz low-pass, 2-4-, 4-8-, and 8-12-kHz band-pass noises, respectively, in5the head-still condition.
(4) Median sound localization performance was 92, 71, 70, 55, 83 and 70% for the broadband,
12-kHz high-pass, 500-Hz low-pass, 2-4-, 4-8-, and 8-12-kHz band-pass noises, respectively, inthe head-movement condition.
(5) Head movement improves localization performance for all stimuli.

ACKNOWLEDGEMENTS
The authors thank the subjects who participated in the experiments. They also thank Mr. Yuki
Sawada for his great effort in building the speaker array used in the experiment. Part of this work
was supported by KAKENHI (22300061).

REFERENCES[1] J. Blauert, Spatial Hearing (The MIT press Cambridge, 1997).
[2] K. Nakabayashi, “Sound Localization on the Horizontal Plane,” J. Acoust. Soc. Jpn., 30(3), 151-160(1974).
[3] G. Arrabito and J. Mendelson, “The relative impact of generic head-related transfer functions and signal
bandwidth on auditory localization: Implications for design of three-dimensional audio displays,”
Defence and Civil Inst of Environmental Medicine, DCIEM-TR-2000-67, 1-31 (2000).
[4] D. Morikawa and T. Hirahara, “Signal bandwidth necessary for horizontal sound localization,” Proc.
20th International Congress on Acoustics, 477.1-477.4 (2010).
[5] M. Morimoto and A. Saito, “On sound localization in the median plane –Effects of frequency range andintensity of stimuli–,” Transactions on Technical Committee of Psychological and Psysioligical
Acoustics, H-40-1-3, 12-17 (1977).
[6] J. Hebrank and D. Wright, “Spectral cues used in the localization of sound sources on the medianplane,” J. Acoust. Soc. Am., 56(6), 1829-1834 (1974).
[7] H. Wallach, “The role of head movements and vestibular and visual cues in sound localization,” J. Exp.
Psychol., 27(4), 339-368 (1940).
[8] F. Wightman and D, Kistler, “Resolution of front back ambiguity in spatial hearing by listener andsource movement,” J. Acoust. Soc. Am., 105(5), 2841-2853 (1999).
[9] D. Begault, E. Wenzel and A. Lee, “Direct Comparison of the Impact of Head Tracking, Reverberation,and Individualized Head-Related Transfer Function on the Spatial Perception of a Virtual Speech
Source,” J. Audio Eng. Soc., 49(10), 904-916 (2001).
[10] Y, Iwaya, Y. Suzuki and D. Kimura, “Effects of head movement on front-back error in soundlocalization,” Acoustical Science and Technology, 24(5), 327-329 (2003).
[11] T. Hirahara, Y. sawada and D. Morikawa, “Impact of dynamic binaural signals on three dimensional
reproduction,” Proc. INTERNOISE (2011).
[12] E. Langendijk and A. Bronkhorst, “Contrivution of spectral cues to human sound localization,” J.
Acoust. Soc. Am., 112(4), 1583-1596 (2002).

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