Introduction

The term ``musical expression'' has become synonymous with those strategies used by musicians to shape their performances. Following are variables that contribute to Musical Expression:

• Changes in instantaneous tempo
• Instantaneous dynamic level
• Inflection of pitch
• Vibrato
• Overlap or separation of successive events (articulation)

A systematic musical expression model that attempts to explain dynamics and timing was suggested by Neil P. Todd circa 1992. It measures force which gives an index of dynamic level and also the times at which keys are depressed, as opposed to measuring the onset times and dynamic levels of acoustic events. In this model the terms instantaneous tempo and velocity are different from global tempo and dynamics. Instantaneous tempo is observed for instance in an actual piano performance.

Relevant to musical expression are performance rules which can also be seen as the strategies each performer has for approaching given compositions. Therefore several performances of the same piece can be correlated to extract changes in in expression.

Musical style is proportional to musical expression but it is out of scope for the purpose of this paper. More on the this topic can be found at David Cope's Experiments in Musical Intelligence.