Generative Composition with Nodal Jon McCormack, Peter McIlwain, Aidan Lane, and Alan Dorin Centre for Electronic Media Art Monash University, Clayton 3800, Australia Jon.McCormack@infotech.monash.edu.au www.csse.monash.edu.au/∼jonmc Abstract. This paper describes a new generative software system for music composition. A number of state-based, musical agents traverse a user-created graph. The graph consists of nodes (representing events), connected by edges, with the time between events determined by the physical length of the connecting edge. As the agents encounter nodes they generate musical data. Different node types control the selection of output edges, providing sequential, parallel or random output from a given node. The system deftly balances composer control with the facilitation of complex, emergent compositional structures, difficult to achieve using conventional notation software. 1 Introduction The goal of any Artificial Life (AL) or generative composition system should be to offer possibilities and results unattainable with other methods. A number of authors have suggested that the emergence of novel and appropriate macro behaviours and phenomena — arising through the interaction of micro compo- nents specified in the system — is the key to achieving this goal [1–3]. While simple emergence has been demonstrated in a number of AL systems, in the case of musical composition, many systems restrict the ability to control and direct the structure of the composition, conceding instead to the establishment of emergence as the primary goal. This focus on emergence exclusively, while interesting in terms of the emer- gent phenomena themselves, has been at the expense of more useful software systems for composition itself. The aim of the work described in this paper is to design and build a generative composition tool that exhibits complex emergent behaviour, but at the same time offers the composer the ability to structure and control processes in a compositional sense. The idea being that the com- poser works intuitively in a synergetic relationship with the software, achieved through a unique visual mapping between process construction and composi- tional representation. This paper describes a new kind of generative music composition system, which we call Nodal (Fig. 1). The system uses spatial, directed graphs that are traversed in real-time by one or more state-based agents, known as players. The players traverse the graphs moving along edges and responding to state changes J. McCormack, P. McIlwain, A. Lane & A. Dorin: "Generative Composition with Nodal", in E.R. Miranda (ed.) Workshop on Music and Artificial Life (part of ECAL 2007), Lisbon, Portugal, 2007.