Previous research on non-speech audio messages called &lt;i&gt;earcons&lt;/i&gt; showed that they could provide powerful navigation cues in menu hierarchies. This work used &lt;i&gt;hierarchical&lt;/i&gt; earcons. In this paper we suggest &lt;i&gt;compound&lt;/i&gt; earcons provide a more flexible method for presenting this information. A set of sounds was created to represent the numbers 0-4 and dot. Sounds could then be created for any node in a hierarchy by concatenating these simple sounds. A hierarchy of four levels and 27 nodes was constructed. An experiment was conducted in which participants had to identify their location in the hierarchy by listening to an earcon. Results showed that participants could identify their location with over 97% accuracy, significantly better than with hierarchical earcons. Participants were also able to recognise previously unheard earcons with over 97% accuracy. These results showed that compound earcons are an effective way of representing hierarchies in sound

Brewster, S.A.

Capriotti, A.

Hall, C.V.

English

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      Brewster, S.A. and Capriotti, A. and Hall, C.V. (1998) Using compound earcons to represent hierarchies. HCI Letters 1(1):pp. 6-8.       http://eprints.gla.ac.uk/3277/     Glasgow ePrints Service http://eprints.gla.ac.uk Using Compound Earcons to Represent HierarchiesStephen Brewster, Adrian Capriotti and Cordelia HallGlasgow Interactive Systems Group, Department of Computing Science, University of Glasgow,Glasgow, G12 8QQ, UK.Tel: +44 (0)141 330 4966, Email: {stephen, capriota, cvh}@dcs.gla.ac.ukWeb: http://www.dcs.gla.ac.uk/~stephen/ABSTRACTPrevious research on non-speech audio messages calledearcons showed that they could provide powerfulnavigation cues in menu hierarchies. This work usedhierarchical earcons. In this paper we suggest compoundearcons can provide a more flexible method for presentingthis information. A set of sounds was created to representthe numbers 0-4 and dot. Sounds could then be created forany node in a hierarchy by concatenating these simplesounds. A hierarchy of four levels and 27 nodes wasconstructed. An experiment was conducted in whichparticipants had to identify their location in the hierarchy bylistening to an earcon. Results showed that participantscould identify their location with over 97% accuracy,significantly better than with hierarchical earcons.Participants were also able to recognise previously unheardearcons with over 97% accuracy. These results showed thatcompound earcons are an effective way of representinghierarchies in sound.INTRODUCTIONIn a previous experiment Brewster et al. [2] showed thatstructured audio messages could provide navigational cuesin situations where graphics were not usable, for exampletelephone-based interfaces such as phone banking, orinterfaces for blind and partially-sighted users.In this previous work hierarchical earcons were used torepresent the structure [1, 3]. By manipulating soundparameters such as instrument, rhythm and tempo soundswere constructed to represent a hierarchy of four levels and27 nodes, (see Figure 1) [2]. However, hierarchical earconshave problems. Making the hierarchy from Figure 1 deeperthan four levels is difficult because once the parametersdescribed have been used then there is nothing left tomanipulate to create new levels. How can this problem besolved? It was decided that compound earcons [1, 3] couldbe used if the hierarchy was represented in a different way.Compound earcons use short sounds for small componentsthat can be concatenated to create longer messages. Theid a of a book was used to represent the hierarchy, withchapt rs, sections and subsections, for example Chapter 1,Section 1.1, Sub-section 1.1.1. Figure 1 shows how this wasmapped on to the hierarchy.A set of simple sounds was created for each of the numbersand dot. The earcon for any node could then simply beconstructed from the concatenation of these sounds. Thismetho  of representing the hierarchy had the advantagethat, with a complete set of sounds to represent thenumbers, any hierarchy of arbitrary size and depth could becreated, overcoming the problem with hierarchical earcons.An experimental investigation was needed to assess theeffectiveness of this method.EXPERIMENTThe same hierarchy used by Brewster  t al. [2] was usedagain so that the results could be compared (see theprevious experiment for more details). Fifteen participantswere used.The main hypothesis was that participants would be able torecall their position in the hierarchy with the same accuracyas in Brewster t al. [2]. Participants should also be able tolisten to an earcon and position it in the hierarchy even ifthey have not heard it before by using the rules from whichMainApplications Word ProcessingGamesGraphics Microsoft WordGeneral programsExperimentsLetters Reports & papersManuals EarconsButtons ExperimentScrollbar Experiment DoomAdventure Arcade GamesPaintWord filesBusiness LettersSeminars Parallel EarconsExperiment dataMystSpace InvadersAB01 2 3 41.1 1.2 1.3 2.1 2.2 2.31.1.1 1.2.1 2.1.1 2.2.13.13.1.1 3.2.13.23.3.13.3 4.14.1.14.24.2.14.34.3.1Figure 1: The hierarchy used in the experiment. The numbers by each node show the position in thehierarchy. A and B mark the new earcons presented to the participants during testing.the earcons were constructed. This would be demonstratedby high rates of recognition when participants werepresented with new earcons.Training and testing were the same as in Brewster et al.’previous experiment so that the results could be directlycompared. Participants had the set of sounds described tothem once and then had five minutes to learn the soundsthemselves. During testing the same set of 14 questions wasused as in Brewster et al.’s experiment. This included thenew, unheard earcons for nodes A and B shown in Figure 1.Sounds usedSimple sounds were constructed to represent the numbers0-4. These were single notes (1 sec. duration) played at C3(261Hz). They were created on a Yamaha TG100synthesiser and played back via HyperCard. The sound for0 was a sitar, 1 was a piano, 2 an orchestral hit, 3 a bell, 4 aflute and marimba for dot. These instruments were chosenbecause each one sounded distinctive and different from allof the others. Earcons for each node in the hierarchy werecreated by concatenating the required sound components.For numbers greater than 4 the instruments would be re-used but the note played two octaves higher. For example, 5would be a note played at C1 (1046Hz) on the sitar. Fornumbers greater than 9 the two motives would be addedtogether, for example 10 would be a piano followed by asitar. This would allow the differentiation of 11 from 1.1because 11 would not have the separator dot between thetwo piano notes. Thus there were five sounds for 0-4, a ruleindicating 5-9, and a sound for dot. This meant that the totalnumber of rules was within the range of 7±2 making themas easy to remember as possible.RESULTSThe overall recall rate of the 12 trained earcons was verygood, with 97% recalled correctly (see Figure 2). This wassignificantly better than the 80% recall rate in [2](F1,22=13.89, p=0.001). The results indicated that compoundearcons were a successful method of presenting hierarchyinformation. The recognition rate of the new, unheardearcons was also good with an average of 97% againrecognised correctly (questions 13-14 in Figure 2). Thisindicates that participants could recognise the newcompound earcons well.DISCUSSIONThis new design for the earcons was significantly betterthan the hierarchical earcons in Brewster et al. [2],indicating that compound earcons can provide effectivenavigation information in hierarchies of information. Theadvantage of using this type of earcons is the possibility ofcreating arbitrarily sized hierarchies The results alsoshowed that new, unheard earcons could be recognised bythe listeners with a high degree of accuracy. This isimportant as it means that users could understand newsounds without being trained on them.One problem that compound earcons have is that they getlonger the deeper one gets into the hierarchy. This maycause several problems. The first is that the user has tolisten to the full earcon before he/she gets the locationinformation. If only part of the earcon is heard, for examplethe user is on node 1.1.1 but decides to move on afterhearing only 1.1, then he/she may become confused aboutthe location. In addition, the longer the sound gets theharder it is to recall. The user will remember the latter partsof the earcon but forget the former, again leading toconfusions about location. Part of the problem of the lengthof compound earcons has been addressed by parallelearcons [4]. These allow the component parts of acompound earcon to be played simultaneously, rather thansequentially. Initial results with compound earcons lookvery promising but more investigations are needed to findthe maximum size of hierarchy that could be representedwith such sounds.REFERENCESSound samples and references by Brewster are availablefrom http://www.dcs.gla.ac.uk/~stephen/1. Blattner, M., Sumikawa, D. and Greenberg, R. Earconsand icons: Their structure and common designprinciples. Human Computer Interaction 4, 1 (1989),11-44.2. Brewster, S.A., Raty, V.-P. and Kortekangas, A.Earcons as a method of providing navigational cues in amenu hierarchy. In Proceedings of BCS HCI'96(London, UK) Springer, 1996, pp. 169-183.3. Brewster, S.A., Wright, P.C. and Edwards, A.D.N. Anevaluation of earcons for use in auditory human-computer interfaces. In Proceedings of ACM/IFIPINTERCHI'93 (Amsterdam) ACM Press, Addison-Wesley, 1993, pp. 222-227.4. Brewster, S.A., Wright, P.C. and Edwards, A.D.N.Parallel earcons: Reducing the length of audiomessages. International Journal of Human-ComputerStudies 43, 2 (1995), 153-175.Question01020304050607080901001 2 3 4 5 6 7 8 9 10 11 12 13 14Compound earconsHierarchical earconsFigure 2: Recall rates for the compound earcons inthis experiment compared to the hierarchical onesfrom Brewster et al. [2]. Questions 1-12 are thetrained earcons and 13-14 are A and B, the newearcons.

An evaluation of earcons for use in auditory humancomputer interfaces.

Earcons and icons: Their structure and common design principles.

Earcons as a method of providing navigational cues in a menu hierarchy.

Parallel earcons: Reducing the length of audio messages.

Sound samples and references by Brewster are available from http://www.dcs.gla.ac.uk/~stephen/

Using compound earcons to represent hierarchies

Enlighten: Publications

 
 
 
 
 
 
Brewster, S.A. and Capriotti, A. and Hall, C.V. (1998) Using compound 
earcons to represent hierarchies. HCI Letters 1(1):pp. 6-8.
 
 
 
 
 
 
 
http://eprints.gla.ac.uk/3277/ 
 
 
 
 
Glasgow ePrints Service 
http://eprints.gla.ac.uk 
Using Compound Earcons to Represent Hierarchies
Stephen Brewster, Adrian Capriotti and Cordelia Hall
Glasgow Interactive Systems Group, Department of Computing Science, University of Glasgow,
Glasgow, G12 8QQ, UK.
Tel: +44 (0)141 330 4966, Email: {stephen, capriota, cvh}@dcs.gla.ac.uk
Web: http://www.dcs.gla.ac.uk/~stephen/
ABSTRACT
Previous research on non-speech audio messages called
earcons showed that they could provide powerful
navigation cues in menu hierarchies. This work used
hierarchical earcons. In this paper we suggest compound
earcons can provide a more flexible method for presenting
this information. A set of sounds was created to represent
the numbers 0-4 and dot. Sounds could then be created for
any node in a hierarchy by concatenating these simple
sounds. A hierarchy of four levels and 27 nodes was
constructed. An experiment was conducted in which
participants had to identify their location in the hierarchy by
listening to an earcon. Results showed that participants
could identify their location with over 97% accuracy,
significantly better than with hierarchical earcons.
Participants were also able to recognise previously unheard
earcons with over 97% accuracy. These results showed that
compound earcons are an effective way of representing
hierarchies in sound.
INTRODUCTION
In a previous experiment Brewster et al. [2] showed that
structured audio messages could provide navigational cues
in situations where graphics were not usable, for example
telephone-based interfaces such as phone banking, or
interfaces for blind and partially-sighted users.
In this previous work hierarchical earcons were used to
represent the structure [1, 3]. By manipulating sound
parameters such as instrument, rhythm and tempo sounds
were constructed to represent a hierarchy of four levels and
27 nodes, (see Figure 1) [2]. However, hierarchical earcons
have problems. Making the hierarchy from Figure 1 deeper
than four levels is difficult because once the parameters
described have been used then there is nothing left to
manipulate to create new levels. How can this problem be
solved? It was decided that compound earcons [1, 3] could
be used if the hierarchy was represented in a different way.
Compound earcons use short sounds for small components
that can be concatenated to create longer messages. The
id a of a book was used to represent the hierarchy, with
chapt rs, sections and subsections, for example Chapter 1,
Section 1.1, Sub-section 1.1.1. Figure 1 shows how this was
mapped on to the hierarchy.
A set of simple sounds was created for each of the numbers
and dot. The earcon for any node could then simply be
constructed from the concatenation of these sounds. This
metho  of representing the hierarchy had the advantage
that, with a complete set of sounds to represent the
numbers, any hierarchy of arbitrary size and depth could be
created, overcoming the problem with hierarchical earcons.
An experimental investigation was needed to assess the
effectiveness of this method.
EXPERIMENT
The same hierarchy used by Brewster  t al. [2] was used
again so that the results could be compared (see the
previous experiment for more details). Fifteen participants
were used.
The main hypothesis was that participants would be able to
recall their position in the hierarchy with the same accuracy
as in Brewster t al. [2]. Participants should also be able to
listen to an earcon and position it in the hierarchy even if
they have not heard it before by using the rules from which
Main
Applications Word 
Processing
Games
Graphics Microsoft 
Word
General 
programs
Experiments
Letters Reports & 
papers
Manuals Earcons
Buttons 
Experiment
Scrollbar 
Experiment Doom
Adventure Arcade 
Games
Paint
Word 
files
Business 
Letters
Seminars Parallel 
Earcons
Experiment 
data
Myst
Space 
Invaders
AB
0
1 2 3 4
1.1 1.2 1.3 2.1 2.2 2.3
1.1.1 1.2.1 2.1.1 2.2.1
3.1
3.1.1 3.2.1
3.2
3.3.1
3.3 4.1
4.1.1
4.2
4.2.1
4.3
4.3.1
Figure 1: The hierarchy used in the experiment. The numbers by each node show the position in the
hierarchy. A and B mark the new earcons presented to the participants during testing.
the earcons were constructed. This would be demonstrated
by high rates of recognition when participants were
presented with new earcons.
Training and testing were the same as in Brewster et al.’
previous experiment so that the results could be directly
compared. Participants had the set of sounds described to
them once and then had five minutes to learn the sounds
themselves. During testing the same set of 14 questions was
used as in Brewster et al.’s experiment. This included the
new, unheard earcons for nodes A and B shown in Figure 1.
Sounds used
Simple sounds were constructed to represent the numbers
0-4. These were single notes (1 sec. duration) played at C3
(261Hz). They were created on a Yamaha TG100
synthesiser and played back via HyperCard. The sound for
0 was a sitar, 1 was a piano, 2 an orchestral hit, 3 a bell, 4 a
flute and marimba for dot. These instruments were chosen
because each one sounded distinctive and different from all
of the others. Earcons for each node in the hierarchy were
created by concatenating the required sound components.
For numbers greater than 4 the instruments would be re-
used but the note played two octaves higher. For example, 5
would be a note played at C1 (1046Hz) on the sitar. For
numbers greater than 9 the two motives would be added
together, for example 10 would be a piano followed by a
sitar. This would allow the differentiation of 11 from 1.1
because 11 would not have the separator dot between the
two piano notes. Thus there were five sounds for 0-4, a rule
indicating 5-9, and a sound for dot. This meant that the total
number of rules was within the range of 7±2 making them
as easy to remember as possible.
RESULTS
The overall recall rate of the 12 trained earcons was very
good, with 97% recalled correctly (see Figure 2). This was
significantly better than the 80% recall rate in [2]
(F1,22=13.89, p=0.001). The results indicated that compound
earcons were a successful method of presenting hierarchy
information. The recognition rate of the new, unheard
earcons was also good with an average of 97% again
recognised correctly (questions 13-14 in Figure 2). This
indicates that participants could recognise the new
compound earcons well.
DISCUSSION
This new design for the earcons was significantly better
than the hierarchical earcons in Brewster et al. [2],
indicating that compound earcons can provide effective
navigation information in hierarchies of information. The
advantage of using this type of earcons is the possibility of
creating arbitrarily sized hierarchies The results also
showed that new, unheard earcons could be recognised by
the listeners with a high degree of accuracy. This is
important as it means that users could understand new
sounds without being trained on them.
One problem that compound earcons have is that they get
longer the deeper one gets into the hierarchy. This may
cause several problems. The first is that the user has to
listen to the full earcon before he/she gets the location
information. If only part of the earcon is heard, for example
the user is on node 1.1.1 but decides to move on after
hearing only 1.1, then he/she may become confused about
the location. In addition, the longer the sound gets the
harder it is to recall. The user will remember the latter parts
of the earcon but forget the former, again leading to
confusions about location. Part of the problem of the length
of compound earcons has been addressed by parallel
earcons [4]. These allow the component parts of a
compound earcon to be played simultaneously, rather than
sequentially. Initial results with compound earcons look
very promising but more investigations are needed to find
the maximum size of hierarchy that could be represented
with such sounds.
REFERENCES
Sound samples and references by Brewster are available
from http://www.dcs.gla.ac.uk/~stephen/
1. Blattner, M., Sumikawa, D. and Greenberg, R. Earcons
and icons: Their structure and common design
principles. Human Computer Interaction 4, 1 (1989),
11-44.
2. Brewster, S.A., Raty, V.-P. and Kortekangas, A.
Earcons as a method of providing navigational cues in a
menu hierarchy. In Proceedings of BCS HCI'96
(London, UK) Springer, 1996, pp. 169-183.
3. Brewster, S.A., Wright, P.C. and Edwards, A.D.N. An
evaluation of earcons for use in auditory human-
computer interfaces. In Proceedings of ACM/IFIP
INTERCHI'93 (Amsterdam) ACM Press, Addison-
Wesley, 1993, pp. 222-227.
4. Brewster, S.A., Wright, P.C. and Edwards, A.D.N.
Parallel earcons: Reducing the length of audio
messages. International Journal of Human-Computer
Studies 43, 2 (1995), 153-175.
Question
0
10
20
30
40
50
60
70
80
90
100
1 2 3 4 5 6 7 8 9 10 11 12 13 14
Compound 
earcons
Hierarchical 
earcons
Figure 2: Recall rates for the compound earcons in
this experiment compared to the hierarchical ones
from Brewster et al. [2]. Questions 1-12 are the
trained earcons and 13-14 are A and B, the new
earcons.


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Using compound earcons to represent hierarchies

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