Information Technology Reference
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What is normally missing in music metadata
is a textual description of the document content
other than its musical structure, which is a peculiar
situation of the music language that is due to the
fact that music is not aimed at describing some-
thing with a known semantic—like text, images,
speech, video or 3D models. This is probably the
main limitation of the use of metadata for music
indexing, and it is the motivation for the number
of content-based approaches proposed in the last
years, compared to textual metadata approaches.
Moreover, it has to be considered that music
representation is aimed at giving directions to
performers and, at least for Western music, is
biased by the characteristics of the music scores
that allows a limited representation of high level
characteristics (Middleton, 2002).
dimensions, in particular the ones that may have
a symbolic representation, which is more suitable
for the creation of an index of a music collection.
For any chosen dimension, the indexing scheme
has to be based on a suitable definition of the
particular lexical units of the dimension and their
representation. A taxonomy of the characteristics
of music and their potential interest for users is
reported in Lesaffre, Leman, Tanghe, De Baets,
De Meyer and Martens (2003).
The representation of the melody can build
upon traditional score representation, which is
based on the drawing of a sequence of notes, each
one with a given pitch and a duration relative to the
tempo of the piece. This symbolic representation
is particularly suitable for indexing, providing
that the melodic lexical units are highlighted.
This is a more difficult task also for musicians
and music scholars; the results of a perceptual
study on manual segmentation are presented in a
following section. The representation of rhythm
can be considered as a variation of melodic
representation, where pitch information can be
discarded or substituted with the information of
the particular percussive instrument that plays
each rhythmic element. Also the indexing of
the harmonic dimension can be based on com-
mon chord representation. In this case there are
alternative representations, from figured bass to
functional harmony and chord names. An over-
view of chord representations, aimed at their an-
notation, is presented in Harte, Sandler, Abdallah
and Gómez (2005). The segmentation of chords
in their lexical units can be based on notions of
harmony, including modulations, cadences, and
the use of particular chord progressions in dif-
ferent music genres.
The analysis of different dimensions and
their representation as building blocks of music
documents may be of interest also for musicolo-
gists, composers and performers. To this end, it
is interesting to cite Humdrum (Huron, 1995),
which apart from retrieval allows a number of
manipulations for analyzing music scores.
music dimensions
Music has a multidimensional nature. Rhythm,
melody and harmony are all well-known dimen-
sions that capture distinctive features of a music
document. These dimensions are conveyed ex-
plicitly by music scores and recognized easily by
listeners of audio recordings, and can be defined
as the
canonical dimensions
of music, because
they are used extensively by music theorists and
musicologists as tools to describe, analyze, and
study music works. Another perceptually relevant
music dimension is timbre, which is related to the
quality of sounds and is conveyed only by audio
recordings. Yet timbre is a multidimensional
feature by itself, and can be described using a
set of continuous parameters, such as spectral
power energy or Mel-Cepstrum Coefficients, and
by perceptually based features such as spectral
centroid, roughness, and attack time. As stated
by Krumhansl (1989), timbre remains a difficult
dimension to understand and represent, though
studies have been carried out on the perception
of timbre similarity (Berenzweig, Logan, Ellis
& Whitman, 2004). The discussion on content-
based music indexing will be limited to canonical
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