Sound Synthesis Theory/Physical Modelling

Physical Modelling Synthesis

Introduction

Physical Modelling synthesis is not confined to a particular technique, but rather represents a family of approaches to synthesis. Physical modelling systems attempt to model the propagation of sound energy in a system, typically starting with a mathematical model or algorithm that is often recursive. Physical modelling techniques often start by attempting to replicate the basic structure of an acoustic instrument and hence mimic the sound it makes when 'excited'. This excitation normally comes in the form of an initial impulse, typically a short burst of noise.

The main advantage of this system is that one can generate convincing acoustic sounds, such as a plucked string or drum hit. Aside from this, other advantages include the ability to tweak parameters (e.g. instrument body density, string length) in order to create specific types of instrument from a generic model. In the extremes, one can specify strange and unrealistic parameters in order to create models of instruments that are impossible to realise physically! Physical modelling systems typically employ delay lines in their structure and this can mean that the output of the system can go out of control and create unwanted feedback.

The Karplus-Strong Algorithm

Alexander Strong and Kevin Karplus developed software and hardware implementations for this algorithm, naming it "Digitar" synthesis.