Music Scope Headphones: Natural User Interface for Selection of Music
Masatoshi Hamanaka

Seunghee Lee

Presto, Japan Science and Technology Agency
A.I.S.T. Mbox 604 1-1-1 Umezono,
Tsukuba, Ibaraki, 305-8568 Japanm.hamanaka@aist.go.jp

University of Tsukuba
Tennoudai 1-1-1,
Tsukuba, Ibaraki, 305-8574, Japan
lee@kansei.tsukuba.ac.jp

Abstract

given to finding songs one has an affinity for from the list.
Musicream [7], on the other hand, make it possible tointeract with many music collections by applying
operations and providing functions for the order of play.
Papipuun [8] and SmartMusicKIOSK [9] provide a musicsummary and allow quick listening in a manner similar toa stylus skipping on a scratched record. All these systems[7-9] enable us to save time by previewing songs from alist of rankings acquired from the results of music retrieval.
However, these systems also force us to listen to songs one
by one and involve many mouse operations.
In contrast, our system, called Music Scope Headphones,
make it possible to select a musical source from the many
available without the need for mouse clicks or other visual
manipulations by detecting natural movements when users
are listening to music and focusing on the particular
musical source that they want to hear. The Music Scope
Headphones provide a novel music selection interface thatenables the following three functions to be applied.
1. Scoping function: enable us to scope many musicalsources allocated in 2-dimensional space by moving
our heads left or right or by looking up or down. The
function enables us to landscape songs and save timein previewing them.
2. Focusing function: highlights a particular musicalsource that users want to hear by them placing theirhand behind an ear. This function enables us tonarrow the area in which sources are audible in 2dimensional space as if controlling the directivity of a
microphone.
3. Switching function: seamlessly changes musicalsources in 2-dimensional space through users’
gestures such as them nodding or shaking their heads,
turning them around, or leaning them to one side. For
example, when users are turning their head around,the next 10 musical sources in the order on the list
acquired from a music retrieval system will beallocated in 2-dimensional space.
We mounted three sensors to the headphones, i.e., adigital compass, a tilt sensor, and a focus sensor, which
detect natural movements, such as that of the head or theplacement of a hand behind an ear, and this allowed us to
use these three functions without the need for a display or
a computer mouse. Users are freed from mouse operations
and can select music much more actively.

This paper describes a novel audio only interface forselecting music which enables us to select songs without
having to click a mouse. Using previous music playerswith normal headphones, we can hear only one song at atime and we thus have to play pieces individually to selectthe one we want to hear from numerous new music files,
which involves a large number of mouse operations. The
main advantage of our headphones is that they detectnatural movements, such as the head or hand moving whenusers are listening to music and they can focus on aparticular musical source that they want to hear. By
moving their head left or right, listeners can hear thesource from a frontal position as the digital compass
detects the change in the direction they are facing. By
looking up or down, the tilt sensor will detect the change
in the face’s angle of elevation; they can better hear thesource that is allocated to a more distant or closer position.
By putting their hand behind their ear, listeners can adjust
the focus sensor on the headphones to focus on a particular
musical source that they want to hear.
Keywords: Headphones, music interface, digital compass,tilt sensor, infrared distance sensor.

1. Introduction
Although we have recently been able to download a huge
number of songs through Internet music delivery services,
users are only listening to a small number because
opportunities to find unfamiliar musical pieces in thecollection are limited. Our goal was to construct a systemthat would enable people to easily select musical sourcesthat they had an affinity for from many unknown ones.
Previous music retrieval methods that use queries suchas similarity-based [1-3] searching, text-based searching[4], or collaborative filtering based searching [5, 6] areuseful for narrowing the number of musical pieces, but
after the list of rankings has been provided we have to listen
to songs one by one because no consideration has been
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© 2006 University of Victoria

Previously reported headphones with sensors to detectthe direction users were facing or the location of the head
could improve the sense of musical presence and create arealistic impression, but could not highlight parts
according to their wishes [10-12]. It was difficult to clearlyhear a particular musical source from many other sources
with these headphones, including some that users may
have preferred not to hear. There are music spatialization
systems [13, 14] that allow users to control the localizationof each part in real time through a graphical interface.
However, it is difficult to control each musical source’s
location through this interface.
This paper is organized as follows. Section 2 explains
the functions of the headphones. Section 3 describes
system processing, and Section 4 discusses theimplementation. Sections 6 and 7 present the experimental
results and the conclusion.

turned its panpot to the center, while decreasing the volume ofthe other sources and turning their panpots left or right. In
this way, a user can easily scope a particular musical source.
2.2 How motion is detected
Natural movements must be detected while the user islistening to music to control the audio mixer through them.
To enable this, we mounted the digital compass and the tilt
sensor on top of the headband to detect the direction theuser was facing and to detect the face's angle of elevation.
We also mounted the focus sensor on the outside of theright speaker to detect the distance from the hand to the ear(Figure 1). We prepared three focus sensor prototypes andevaluated how practical they were in an experiment.
(c) Focus sensor(a) Digital Compass(Infrared distance sensor)

2. Music Scope Headphones
We constructed the Music Scope Headphones that enabled
us to save time in previewing songs based on the following
three policies.
Reduced mouse operations When selecting music with acomputer, we generally have to play songs individuallywith many mouse operations and these interrupts break theprocess of listening just as if a telephone were ringing. To
solve this, we propose operations without mouse clicks
achieved by detecting natural movements when listening tomusic and using these to control the computer.
Easy preview of many songs We wanted to increase thenumber of opportunities for encountering unfamiliarmusical pieces in collections. However, the number ofsongs that can be previewed is limited within a fixedamount of time. This is because the larger the number ofsongs to be previewed, the shorter the time to listen to eachsong. To solve this, we propose a novel way of selecting
music by playing many musical sources at the same time.
No computer display We wanted the system to be usedanywhere and at any time such as at work or when riding or
walking without the need to see a computer display. We
attempted to construct a system to investigate whether it werepossible to select and manipulate songs without a display.
The Music Scope Headphones let users control an audio
mixer through natural movements, and thus enable them toselect a musical source that they want to listen to fromnumerous sound sources. We will now explain the
problems and solutions we encountered with the Music
Scope Headphones based on these policies.
2.1 How musical sources are scoped
A particular musical source that the user temporarily wants tohear must be differentiated from other musical sources to scope
it. We automatically adjusted each musical source's volume
and panpot so that it could be distinguished from othermusical sources. That is, we increased that source's volume and(b)Tilt sensor

Figure 1. Three sensors mounted to headphone.

2.3 How function and motion are linked
How usable the Music Scope Headphones are depends on
the quality of the links between the functions and theusers’ natural movements while they are listening to music.
Let us imagine the following scenario.
•
We receive several session recordings from achildhood friend.
•
It sounds like the friend is playing a saxophone on
one of these recordings.
In such a case, we would ordinarily search for songs with asaxophone part, and we then might want to hear the
saxophone playing more clearly. We used the three links
that follow to achieve this.
Link for scoping function When users move their headleft (right), the musical source normally heard from the left
(right) side can be heard from the frontal position as thedigital compass detects the change in the direction they arefacing. This allows users, through natural movements, toscope the musical source they want to hear most clearlyand hear it from the front. When there are several musicalsources at the front, users might not be able to hear thedesired source clearly even after turning their head left or
right to hear it from the front. In such a case, they canchange the mix by moving their head up or down; the tilt
sensor will detect the change in the face's angle ofelevation. By looking up or down, users can increase thevolume of sources so that instruments appear farther awayor nearer. Here, we changed each source's position in 2dimensional space, as can be seen in the graphical userinterface in Figure 2. The circle at the center indicates theposition of the user's avatar and his/her head direction, andthe circled numbers around the avatar indicate thepositions of the sources. We also had several preset
allocations for musical sources and these were easy tochange by putting one's head to one side (Figure 3).
⑤

their head around in the song selection mode, the songs
allocated in 2-dimensional space change to the next 10
songs from the list (Figure 4 (d)).
(d) Changes to the next 10 songs(b) Return to the previous mode of situation

⑥

④

⑦

(a) Select the focusing songs

Position of musical sources
⑧

③

⑨

②
①

Avatar(currently looking forward)⑩

Figure 2. GUI for locating positions of parts.
(a) Circle(b) Star(c) Band(d) Orchestra

Figure 3. Presets for allocation.

Link for focusing function The focus sensor is used to detect
the motion of users putting their hand behind an ear while they
are listening to sound coming from the frontal position. The
distance between the hand and ear determines the area in whichsources are audible. For example, when users place their handclose to their ear, they can only hear the sources from thefrontal position. When they removes their hand, they can hear
all the sources except those behind them. When they put theirhand in the middle position, they can hear the sources located in
the front half position. By adjusting the distance between theirhand and ear in this way, they can control the focus level andhighlight the source of interest.
Link for switching function The system has two modes, asong selecting mode and a part scoping mode. We canscope and preview 10 songs in the song selecting mode
from those listed in order by a music retrieval system
allocated in 2-dimensional space. When converging on
several songs using the focusing function in the songselecting mode, users can leave focused songs and delete
unfocused songs by nodding their head (Figure 4(a)). If
they want more convergence, they only need to adjust thefocus level and nod their head again. Conversely, users candefocus by shaking their head and return to the previous
scenario (Figure 4 (b)). When they only select one songand have a sound source where the tracks for each part
have been recorded separately, the system changes to thepart scoping mode. The Music Scope Headphones provide
novel entertainment with this mode through which users
can "scope" onto the part they want to hear more clearly.
They can return to the song selection mode by shaking
their head. Users can change the preset allocation by
putting their head to one side (Figure 4 (c)) during thesong selecting mode or the part scoping mode. By turning(c) Change the allocation of themusical source by presets allocation

Figure 4. Link for switching function.

3. Processing
This section describes the processing flow for the system.
We mainly describe sound processing and have omitted
explanations for detecting gestures, nodding, shaking,putting the head to one side, and turning it around becauseof word limitations. In the following, we use θ (-π ≤ θ < π)as the facing direction detected by the digital compass, φ(-π ≤ φ < π) as the face's angle of elevation detected by
the tilt sensor, and δ (0 ≤ δ ≤ 1) as the distance between thehand and the ear detected by the focus sensor (Figure 5). We
use radians as angle units and set the starting direction andangle of elevation to zero. We normalized δ from 0 to 1, andthe focus sensor could detect a distance from 0 to 3 cm.
When the distance was 0 cm, δ was output as 0, and when
the distance was 3 cm, δ was output as 1. When the distancewas between 0 and 3 cm, δ ranged from 0 to 1.
z

y

θ φ
δ

x

Figure 5. Three sensors mounted to headphone.

Pretreatment We prepared sound source Sn by recording aseparate track for each part and allocating a position on thegraphical user interface to each part (Figure 2). Here, ln (0 ≤ln ≤ 1) indicates the distance from the avatar to each partand θn indicates the direction of each part. We normalized
ln so that the most distant part would have a value of 1.
Step 1 h nφ(0 ≤ h nφ ≤ 1) was calculated as the amplification
rate for each part, n , which changes depending on the angleof elevation, φ . We used the following formula so that whenusers looked up (down), the volumes of parts located far
from (near to) their position would increase.
~⎧0hnφ < 0⎪~(1)hnφ = ⎨hnφ0 ≤ hnφ < 1~⎪1
1 < hnφ ,
⎩
where

~
1
hnφ = 1 + l n sin φ − ∑ l m sin φm m
m: number of parts.
When we allocated the positions for all parts as in Figure
6 (a), the mixing console was as in Figure 6 (b) when φ was
zero. When φ was negative, the mixing console was as in
Figure 6 (c), indicating that the volume of parts locatednear to (far from) the avatar was increased (decreased).
(a) Position ofmusical sources(b) Looking
horizontally

When we allocated the positions of all parts as in Figure 2,
the mixing console was as in Figure 8(a) when users werelooking left, as in Figure 8(b) when they were looking straightahead, and as in Figure 8(c) when they were looking right.
(a)Looking left(b) Looking at center(c) Looking right(c) Looking down

Figure 8. Direction θ and mixing console.
⑥

⑦

⑧

⑨

We used an adjustable parameter, α (0 ≤ α < 1), to
decrease the amplification rate when users placed theirhand on their ear and δ < 1. When we allocated positions
for all parts as in Figure 2, the mixing console was as in
Figure 9 (a) when users moved their hand away from theirear, and as in Figure 9 (b) when they moved their hand
toward their ear.

⑩

① ② ③ ④ ⑤

Figure 6. Angle of elevation φ and mixing console.

(a)Removing hand from ear (δ = 0)(b) Hand approaching ear (δ > 0)δ

Step 2 h n was calculated as the amplification rate for allparts n, which changes according to the distance between
the hand and ear δ. Here, |a| indicates the absolute valueof a, and θ n ’(－π ≤ θ n ’< π) indicates the angle
between θn and θ.
⎧1π ⋅ δ ≥ θ n′⎪(2)δhn = ⎨′π ⋅δ < θn⎪0⎩For example, h nδ= 0 corresponds to the parts located behindthe user and h nδ=1 corresponds to the parts in front of theuser when θ = π/3 and δ = 0.5 (Figure 7). In this way, we
can eliminate parts the user does not want to hear.
⑤

⑥

⑦
⑧

④
③

h nδ＝1

②
①

⑨
⑩

⑪

hnδ＝0

Figure 7. Distance from hand to ear δ and h nδ.

Step 3 h n θ (0 ≤ h n θ ≤ 1) is calculated as theamplification rate for all parts n, which changes according
to the direction. The h nθ output has a large value when
the part is located in front of the user and becomes smallerwhen the part is located in another direction.
~⎧0hnθ < 0(3)hnθ = ⎨ ~ θ
~θ
0
≤
,
h
h
n
⎩ n
where
δ =0
0
⎧⎪
hnθ = ⎨ α ⋅ θ n′1−
δ > 0.
⎪⎩π ⋅δ

Smooth distribution

Sharp distribution

Figure 9. Decreasing amplification rate while α > 0.

Step 4 ｐ n (0 ≤ ｐ n < 1)is calculated as the left/rightvolume ratio depending on direction θ . Here, ｐ n = 0
indicates that the ratio is 0:1 and ｐn = 0.5 indicates that itis 1:1. We used an adjustable parameter, β, to change theleft/right ratio when the users put their hand to their ear
and δ < 1. When β> 0 and δ < 1, the panpots of the parts
move to the back except for the part in the frontal position,and users can hear music as if focusing on the front part.
′1 β ⋅θn(4)pn = +
2 π ⋅δ
Step 5 The amplification rates acquired in Steps 1 to 4
are multiplied and then the sound is output by summingup the sounds of all parts.
Right-side output:(5)
S Right = ∑ S n ⋅ hnφ ⋅ hnδ ⋅ hnθ ⋅ p n andnLeft-side output:
S Left = ∑ S n ⋅ hnφ ⋅ hnδ ⋅ hnθ ⋅ (1 − p n ) .

(6)n4. Implementation
We presented the processing flow for the software in theprevious section. It worked on the Max/MSP [16]. Here,
we describe the implementation of the hardware. We
implemented the headphones with the two policies that
follow so that everyone can easily use them.

•Lightweight yet strong.
•
Easily connected to computer.
Headphones We selected headphones (Zenhizer:
HD212Pro) that had adjusters inside the headband,
because we could mount the focus sensor outside the rightheadband and this would therefore work stably even if the
speakers were moved (Figure 1).
Sensors
We mounted the attitude detection module(Aichi Micro Intelligent: AMI302-ATD) to the top of theheadband, which consisted of the digital compass (MIsensor) and tilt sensor (Figure 1 (a), and (b)). Generally,
the larger the angles of elevation, the larger the margin forerror in the digital compass, because it detect the directionof the magnetic line of force. The main advantage of using
the module was that the tilt sensor could correct the outputof the digital compass. The detection resolution for themodule was 2 degrees.
We also mounted the focus sensor to the right of theheadband. We compared three focus-sensor prototypes inthe experiments with musical novices, which are described
below, and we selected the infrared distance sensor (Sharp:
GP2S40J) (Figure 1 (c)). The infrared distance sensor
consists of illuminant and acceptance of infrared andmeasures the distance between the sensor to objects by
accepting the reflecting infrared. We prepared a circuit for
mounting the infrared distance sensor and we mounted asemi-variable resistor so that the sensor could detect from0 to 3 cm.
Protectors We made protectors for the sensor out ofacrylic resin (Figure 1). We tested several colors for the
resin and selected a light pink because this was affected
least by sunlight from the windows and it widened thedetection range of the sensor.
Circuit We integrated the information from the sensors byusing a microcomputer (Renesas: R8C/15) mounted inside theheadphone speaker housing and it output a serial signal. We
could therefore reduce the number of cores in the cable fromthe headphone to the computer. The microcomputer sent a
signal with output information from the sensors every 120 ms.
USB conversion We used a USB converter (Silicon Labs.:
CP2102), which converted the serial signal to USB. It was
mounted in the middle of the cable from the headphones toenable easy connection to the computer. We mounted LEDs
on all sensors to indicate whether they were connected to thecomputer. If there was a connection they blinked quickly
and if there was no connection they blinked slowly and we
had to re-connect the USB cable.
Power supply All the sensors and the microcomputer
worked on the bus current of the USB, which simplified
the connection of the headphones. All we needed were theheadphones and the computer.

5. Experimental Results
We designed the Music Scope headphones to enable not only
a particular song to be selected from an ordered list acquired

from music retrievals but also to highlight a particular
instrument in the selected song that a user may want to hearmore clearly. The system allows both audio files and MIDI
files. In the experiments, we used RWC music database,which contains raw audio data before mix-down [15].
5.1 Evaluation of usability of focus sensors
Here, we discuss our evaluation of how usable the threefocus-sensor prototypes were. They were (a) a variable
resistor, (b) a bend sensor on a plastic lever, and (c) an
infrared distance sensor (Figure 10). All headphones sets
used the same digital compass and tilt sensor. We asked
three musical novices to find a particular instrument,
which we specified randomly, while listening to a songusing the headphones. We used the song RWC-MDB-J2001 No. 38 [15], which was played by 10 instruments
located around the avatar as in Figure 2. The subjects
already knew the sound of each instrument and wereallowed to use all headphones several times before theexperiment to familiarize themselves with their operation.
The adjustable parameters α and β described in Section 3
were tuned by the subjects as they wanted. The following
describes one trial of the experiment.
(1) Before the song was started we specified an
instrument to subjects.
(2) We started the song at a midpoint randomly selected
for the specified instrument.
(3) We measured the time the subjects needed to find the
instrument.
The location of all instruments were randomly changed atevery trial. The musical novices changed their headphones
after every 10 trials.
(a)Variable resistor (b) Bend sensor (c) Infrared distance sensor

Figure 10. Three types of focus sensors .

Table 1 lists the average results from 100 trials. While thebend sensor was no less accurate than the variable resistor or
the infrared sensor, it was attached to a plastic lever, which
made it difficult to precisely control. Subjects A and C could
find an instrument more quickly when using the infrared
focus sensor. Subject B, on the other hand, could find an
instrument more quickly when using the variable resistor.
We selected the infrared distance sensor because the averagetime for the three subjects was the shortest.
Table 1. Comparison of three kinds of focus sensors.
Subject A
Subject B
Subject C
Average

Variable resistance
1.84 sec.
0.72 sec.
1.02 sec.
1.19 sec.

Bend sensor
1.28 sec.
1.04 sec.
2.01 sec.
1.44 sec.

Infrared distance sensor
1.12 sec.
0.84 sec.
0.74 sec.
0.90 sec.

5.2 Evaluations of usability for selecting songs
We evaluated whether users could select a song by using theMusic Scope Headphones. We asked three musical novices tofind a song with a soprano saxophone from the RWC-MDB-J2001 database [15]. It had fifty jazz songs and only one song
had a soprano saxophone part. We measured the time thesubject needed to find the soprano saxophone. The subjects had
not heard the songs on the database before the experiment
except for RWC-MDB-J-2001 No. 38, which we had used in
the experiment in Section 5.1. After measuring the time using
the Music Scope Headphones, we measured the time for same
trial using Windows Mediaplayer, which is a standard music
player pre-installed in Windows XP. The time for each subject
to find the musical instrument was only measured one for theMusic Scope Headphones and Windows Mediaplayer.
Table 2 lists the results obtained with the Musical Scope
Headphones and Windows Mediaplayer. All the subjects could
find the song more quickly when using our Music Scope
Headphones, but Windows Mediaplayer was handicapped
because the subjects may have memorized the songs in the firsttrial with the Music Scope Headphones. As a result, ourexperiment revealed that the Music Scope Headphones weresuperior for previewing songs from an ordered list.
Table 2. Comparison of our system and standard music player.
Subject A
Subject B
Subject C
Average

Music Scope Headphones
224 sec.
423 sec.
642 sec.
429 sec.

Windows Media Player
845 sec.
1145 sec.
751 sec.
914 sec.

6. Conclusion
The Music Scope Headphones enabled wearers to control an
audio mixer through natural movements that enabled them not
only to select a song from an ordered list acquired from music
retrievals but also to highlight a particular instrument in theselected song that they wanted to hear more clearly. Three
sensors were mounted to the headphones: a digital compass, atilt sensor, and a focus sensor for detecting natural movements.
This freed users from mouse operations so they could selectmusic much more actively. We tested how usable three kinds
of focus sensors were and found that an infrared distancesensor was better than either a variable resistor or a bend sensor
from the average time it took three subjects to locate an
instrument. We also tested how efficiently the headphones werein selecting songs and the results revealed that they performed
better than the standard Windows Mediaplayer by being able toselect a particular song from fifty others.
We are now developing other applications for theheadphones. Figure 11 shows where the light’s brightness has
been controlled according to the sound level at the music
stands. This allows the user to experience all sound levels
visually as well as aurally. This should help musical novices
who do not know what individual instruments sound like tolearn the relationship between these and the entire piece. The
video is available at http://staff.aist.go.jp/m.hamanaka/video/.

We plan to use these headphones with music retrieval
based on voice recognition to construct a system in whicha display and a mouse are unnecessary.

Figure 11. Lighting depending on sound levels at music stands.

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