Application of a Musical Robot for Adjusting Guitar String Re-Excitation Parameters in Sound Synthesis

Marek Janusz Pluta,Daniel Tokarczyk,Jerzy Wiciak

doi:10.3390/app12031659

Abstract

Sound synthesis methods based on physical modelling of acoustic instruments depend on data that require measurements and recordings. If a musical instrument is operated by a human, a difficulty in filtering out variability is introduced due to a lack of repeatability in excitation parameters, or in varying physical contact between a musician and an instrument, resulting in the damping of vibrating elements. Musical robots can solve this problem. Their repeatability and controllability allows studying even subtle phenomena. This paper presents an application of a robot in studying the re-excitation of a string in an acoustic guitar. The obtained results are used to improve a simple synthesis model of a vibrating string, based on the finite difference method. The improved model reproduced the observed phenomena, such as the alteration of the signal spectrum, damping, and ringing, all of which can be perceived by a human, and add up to the final sound of an instrument. Moreover, as it was demonstrated by using two different string plucking mechanisms, musical robots can be redesigned to study other sound production phenomena and, thus, to further improve the behaviours of and sounds produced by models applied in sound synthesis.

Highlights

Among the various methods of sound synthesis applied for musical purposes, one of the most powerful and versatile is based on numerical modelling of actual musical instruments [1,2]
In general, sound synthesis aims at the sound itself, and its parameters are related to acoustic signal or its underlying abstract model, in physical modelling synthesis, parameters have actual physical counterparts, related mostly to the geometry and material of the object in question, or to the excitation of its vibrating elements
Methods based on physical modelling, can advance towards the better reproduction of sounds of acoustic instruments only through an understanding of the underlying acoustic phenomena

Summary

Introduction

Among the various methods of sound synthesis applied for musical purposes, one of the most powerful and versatile is based on numerical modelling of actual musical instruments [1,2]. Such method is commonly referred to as physical modelling sound synthesis, and is often implemented on the basis of finite difference simulations [1], waveguides [3,4,5,6,7], or modal techniques [8]. Simplifications are common, yet, still, important instrument features need to be considered Some instruments, such as the grand piano, have been studied relatively well, to the level of subtle effects such as unison impact, inharmonicity, double decay, or reexcitation [9,10,11]. There is less data regarding some of the more subtle effects for the acoustic guitar, probably due to lack of appropriate test stands, in which a guitar could be mounted in a stable way, and excited in a repeatable, controllable manner

Methods

Discussion

Conclusion