Parameter Estimation of a Plucked String Synthesis Model Using a Genetic Algorithm with Perceptual Fitness Calculation
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Parameter Estimation of a Plucked String Synthesis Model Using a Genetic Algorithm with Perceptual Fitness Calculation Janne Riionheimo Laboratory of Acoustics and Audio Signal Processing, Helsinki University of Technology, P.O. Box 3000, FIN-02015 HUT, Espoo, Finland Email: [email protected]
¨ ¨ Vesa Valim aki Laboratory of Acoustics and Audio Signal Processing, Helsinki University of Technology, P.O. Box 3000, FIN-02015 HUT, Espoo, Finland Pori School of Technology and Economics, Tampere University of Technology, P.O. Box 300, FIN-28101, Pori, Finland Email: [email protected] Received 30 June 2002 and in revised form 2 December 2002 We describe a technique for estimating control parameters for a plucked string synthesis model using a genetic algorithm. The model has been intensively used for sound synthesis of various string instruments but the fine tuning of the parameters has been carried out with a semiautomatic method that requires some hand adjustment with human listening. An automated method for extracting the parameters from recorded tones is described in this paper. The calculation of the fitness function utilizes knowledge of the properties of human hearing. Keywords and phrases: sound synthesis, physical modeling synthesis, plucked string synthesis, parameter estimation, genetic algorithm.
1. INTRODUCTION Model-based sound synthesis is a powerful tool for creating natural sounding tones by simulating the sound production mechanisms and physical behavior of real musical instruments. These mechanisms are often too complex to simulate in every detail, so simplified models are used for synthesis. The aim is to generate a perceptually indistinguishable model for real instruments. One workable method for physical modelling synthesis is based on digital waveguide theory proposed by Smith [1]. In the case of the plucked string instruments, the method can be extended to model also the plucking style and instrument body [2, 3]. A synthesis model of this kind can be applied to synthesize various plucked string instruments by changing the control parameters and using different body and plucking models [4, 5]. A characteristic feature in string instrument tones is the double decay and beating effect [6], which can be implemented by using two slightly mistuned string models in parallel to simulate the two polarizations of the transversal vibratory motion of a real string [7].
Parameter estimation is an important and difficult challenge in sound synthesis. Usually, the natural parameter settings are in great demand at the initial state of the synthesis. When using these parameters with a model, we are able to produce real-sounding instrument tones. Various methods for adjusting the parameters to produce the desired sounds have been proposed in the literature [4, 8, 9, 10, 11, 12]. An automated parameter calibration method for a plucked string synthesis model has been proposed in [4, 8], and then improved in [9]. It gives the estimates for the fundamental frequency, the decay parameters, and the excitation signal
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