Information Technology Reference
In-Depth Information
8.3.1.
Sound representation of the hierarchical level
8.3.1.1.
Earcons
The notion of earcon was introduced by the works of Blattner
et al
. [BLA 89]
and corresponds to a sound used to carry an information in a non verbal way. The
relationship between the earcon and the meaning is posed arbitrarily and must
therefore be learned by listeners. The authors thus propose the construction of
earcons based on musical motifs of which five parameters enable the signification of
the motif to be varied: the dynamic (i.e. the range of the variation of intensity); the
rhythm (i.e. the temporal organization of sounds); the pitch (fundamental
frequency); the tone (i.e. the type of instrument used), and the register (i.e. the range
of variation in pitch).
Brewster [BRE 95a] then proposed a series of specifications for the creation of
earcons on the basis of these five parameters to which spatialization and sound
effects are added. For a given level of hierarchical depth, these different musical
parameters enable the elements that make up this level to be differentiated:
- level 1: the use of different tones of instruments, the register and spatialization
(e.g.: stereo position);
- level 2: use of different rhythms, tempos and durations;
- level 3 and lower: use of the pitch, intensity, different chords and sound effects
(e.g. reverberation) to differentiate items.
8.3.1.2.
Hierarchical earcons according to Brewster
On the basis of the parameters described above, Brewster [BRE 98a] tested
different methods to represent the hierarchical structure of a menu comprising
several levels of depth.
An initial level of earcons for a small hierarchy of files is presented in Figure
8.4. The files that come from the same family share the same tone, and the files of
the same type share the same rhythm.
Brewster then proposes a method to represent a hierarchy of files this time
comprising four levels of 27 nodes. The hierarchy and associated sounds are
represented in Figure 8.5. This figure shows that level 2 is represented through three
parameters: the tone, the stereo position and the register. For levels 1 and 2, the
sound associated with each item is continuous. Then, level 3 uses rhythm to
differentiate each sub-menu, which inherits the properties of the item above. Three
different rhythms are used, as presented in Figure 8.5. Level 4 is a replica of level 3
with a more rapid repetition of motifs.
