Introduction to the rules for music performance

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.