Abstract Physical modeling and model-based sound synthesis have recently been among the most active topics of computer music and audio research. In the modeling approach one typically tries to simulate and duplicate the most prominent sound generation properties of the acoustic musical instru- ment under study. If desired, the models developed may then be modified in order to create sounds that are not common or even possible from physically realizable instruments. In addition to physically related principles it is possible to combine physical models with other synthesis and signal pro- cessing methods to realize hybrid modeling techniques. This article gives an overview of some recent results in model- based sound synthesis and related signal processing tech- niques. The focus is on modeling and synthesizing plucked string sounds, although the techniques may find much more widespread application. First, as a background, an advanced linear model of the acoustic guitar is discussed along with model control principles. Then the methodology to include inherent nonlinearities and time-varying features is intro- duced. Examples of nonlinearities are studied in the context of two string instruments, the kantele and the tanbur, which exhibit interesting nonlinear effects. 1 Introduction Physical modeling and model-based sound synthesis have been studied with increasing activity twenty-thirty years (Hiller & Ruiz, 1971; Jaffe & Smith, 1983; Smith, 1983; Smith, 1996). For sound synthesis purposes the aim of modeling is to find signal processing algorithms that imple- ment the physically and perceptually most important proper- ties of a specific instrument or of a family of instruments, enabling real-time synthesis with good fidelity. The approach has been most successful in modeling of one-dimensional acoustic resonators that can be considered as linear and time- invariant (LTI) systems. Vibrating strings and air columns are good examples thereof (Fletcher & Rossing, 1991). Two-dimensional acoustic systems, such as membranes and plates, as well as three-dimensional resonators, such as rooms, have also been modeled successfully, although com- putational complexity grows rapidly with dimensionality. Memoryless nonlinearities have been added to model- based synthesis, too. For example reed functioning in wind instruments can be realized this way fairly accurately (Smith, 1987; Välimäki et al., 1992; Cook, 1992). Also the interac- tion between piano hammer and string has been simulated with models where the nonlinearity happens in a single point and is computed as parameter changes at specific time moments only (Van Duyne et al., 1994). More general forms of nonlinearity and signal-dependent time variance, i.e., non- LTI modeling, have not yet progressed very far. There are several reasons to this: (a) nonlinear models tend to be spe- cific cases and a general methodology cannot be as system- atically formulated as for LTI systems, (b) building nonlinear models and estimating their parameters is inherently more difficult than for LTI systems, and (c) real-time computation of nonlinearities requires usually more processing power than LTI models. Due to rapid progress in processor capacity, however, the non-LTI approach is becoming increasingly attractive since it allows for improved reality and nuances in model-based sound synthesis. Accepted: 4 April, 2001 Correspondence: Matti Karjalainen, Helsinki University of Technology, P.O. Box 3000, FIN-02015, HUT, Finland. Tel. +358 9 451 2490; Fax: +358 9 460 224; E-mail: matti.karjalainen@hut.fi An Overview of New Techniques and Effects in Model-based Sound Synthesis Matti Karjalainen 1 , Tero Tolonen 2 , Vesa Välimäki 1 , Cumhur Erkut 1 , Mikael Laurson 3 and Jarmo Hiipakka 4 1 Helsinki University of Technology, Laboratory of Acoustics and Audio Signal Processing, P.O. Box 3000, FIN-02015, HUT, Finland; 2 Luxxon, 500 Ellis Street, Mountain View, CA 94043, USA; 3 Sibelius Academy, Centre for Music Technology, P.O. Box 86, 00251, Helsinki, Finland; 4 Nokia Research Center, Itämerenkatu 11-13, 00180 Helsinki, Finland Journal of New Music Research 0929-8215/01/3003-203$16.00 2001, Vol. 30, No. 3, pp. 203–212 © Swets & Zeitlinger Downloaded By: [TKK Elektroniikan Tietoliikennetekniikan &] At: 07:00 7 September 2009