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  • pDM:An Expressive Sequencer with Real-Time Control of the KTH MusicPerformance Rules
  • Anders Friberg

Experimental research in music performance is now an established field with a number of interesting advances relating to the understanding of the musical communication between performer and listener (Palmer 1997; Gabrielsson 1999). Research in this field includes the communication of structure (Friberg and Battel 2002), emotional expression (Juslin 2001), and musicians' body gestures (Davidson and Correia 2002; Wanderley et al. 2005; Dahl and Friberg forthcoming). From this research, it is evident that the performer has an important and essential role "giving life" to a composition by introducing gestural qualities, enhancing the musical structure, and providing a personal interpretation reflecting an expressive intention. For example, studies of emotional expression have shown that the same piece can communicate completely different emotions by changing the performance.

A part of this research field has attempted to find and model the underlying performance principles used by the musicians (De Poli 2004; Widmer and Goebl 2004). One such system, the KTH rule system for music performance, is a result of a long-term research project initiated by Johan Sundberg (Sundberg et al. 1983; Friberg 1991; Sundberg 1993). The KTH rule system currently consists of about 30 rules covering different aspects of music performance. The input is a symbolic score, and the output is the expressive rendering in which the performance parameters such as "microtiming," articulation, tempo, and sound level are shaped. The rules model typical performance principles such as phrasing, articulation, intonation, micro-level timing, rhythmic patterns, and tonal tension. High-level musical descriptions, such as emotional or motional expressions, can be modeled by using a selection of rules and rule parameters (Bresin and Friberg 2000). In the first development stage, rules were derived using the analysis-by-synthesis method: using the musician Lars Frydén as an expert judge, the computer was taught how to play more musically by implementing a tentative model, listen to the result, and then go back and make adjustments. Later real performance measurements were also employed later for modeling some of the rules. The project has resulted in about 60 publications, including three doctoral dissertations. (See www.speech.kth.se/ music/performance.)

The program Director Musices represents the main implementation of the rule system. It was designed primarily for research purposes and is not suitable for real-time control. However, realtime control of the rule system has a number of potential applications. It could be used for interactive expressive control of the music in, for example, a conductor style, as is suggested below. Whereas previous conductor systems primarily controlled overall sound level and tempo (e.g., Mathews 1989; Borchers et al. 2004), this system would provide macro-level control of the overall expressive character by changing the musical performance details. Recently, a combination of the Radio-Baton system by Mathews (1989) and the rule system was tested. The score was preprocessed in Director Musices using only the micro-level rules, leaving overall tempo and dynamics to the real-time control (Mathews et al. 2003). This improved the performance, but performance variations like articulation remained static during the performance.

The aim of the present work was to develop the basic tools needed for real-time expressive control of music performance. In this article, the overall method is described, followed by a detailed description of the rule application and the pDM player, the real-time control system including mappers and a gestural interface. The article concludes with a discussion of possible applications aimed toward conductor systems. [End Page 37]

Method Overview

Director Musices (DM) is the implementation containing a major part of the rules (Friberg et al. 2000a). The use of Lisp as the programming language has proven to exhibit a number of advantages for research purposes. In particular, rule prototyping is rather quick and can produce reliable results owing to a number of specialized functions and macros that constitute the programming environment. In using DM, one typically loads a score file, selects a set of rules (the rule palette), applies the rules, and then listens to the result. The resulting performance variations can also be visualized on various graphs. A further description of all the rules...

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