|
If music is performed exactly
as written, a dull, machine-like performance results. When performing
music, musicians deviate slightly but significantly from what is nominally
written in the score. Some of these deviations have been described in
terms of context dependent rules.
For example, one rule states that in sequences of eighth notes, those
in stressed positions be played a little longer than those in unstressed
position. This rule is used both in jazz music and in some Baroque music,
where the phenomenon was called "inégales". Here you can listen to the
effects generated by this and other performance rules in a set of music
excerpts.
The magnitude of the effect generated by a specific rule is determined
by the rule quantity
k.
If the quantity is high,
the effect is great and salient.
Performance rules affect
not only the duration of tones. Some rules alters loudness, change the
exact pitch or the vibrato. Other rules create crescendos and diminuendos,
change the tempo, or insert minute pauses between tones. The effects
induced by a rule can be so subtle that they are very hard to perceive,
or coarse, so that they catch the ear.
To realize how a rule
affects the performance, it is often helpful first to compare a
No Rule
version of an example,
where the rule is not applied, with an Exaggerated
version, where the effect
is great. There is also a
Medium
version, which we regard
as musically preferable, and in some cases an
Inverted,
where the rule is producing
the opposite effect, for instance shortenings instead of lengthenings.
There are three different
types of rules:
Differentiation Rules
enhance the differences between scale tones such as Do Sol, La,
etc, and between note values such as quarter notes, eighth notes etc.
Grouping Rules show
which tones belong together and which do not. In music the "belonging-togetherness"
exists at several levels simultaneously. Tones constituting melodic
gestures, such as belong together, as do tones constituting phrases.
The rules mark, by means of micropauses and lengthening of tones, the
boundaries between all these tone groups.
Ensemble Rules keep
the order in ensembles. They achieve sychronization by lengthening and
shortening the individual tones in the various voices according to a
common overall strategy and they achieve fine tuning of successive and
simultaneous intervals.
The rules represent the combined results from several research projects
about music performance at KTH. Most of them are implemented in the
program Director Musices. Its manual has references to the relevant
papers for each rule, also found in the publication list.
|