Speech and Audio Signal Processing: Processing and Perception of Speech and Music, Second Edition

CHAPTER 12

MUSICAL INSTRUMENT ACOUSTICS

12.1 INTRODUCTION

In Chapter 10, we analyzed wave motion on strings and in acoustic tubes. In Chapter 11, we applied these concepts to model speech production. In this chapter, these ideas will be applied to the study of some musical instruments.

Many instruments use vibrating strings, whereas others use the human breath stream. In the case of speech or singing, the sound we hear is created by the resonances of the vocal tract. Thus, the breath stream represents the excitation that creates the traveling wave that is then modified by the vocal tract resonances. Similarly, the vibrating strings in a string instrument excite the body of the instrument, causing it to vibrate to produce the sounds we hear.

String instruments can be further classified as plucked (guitars, banjos, and harps), bowed (violins, violas, and cellos), or struck (piano), and these differences in excitation have a significant effect: Plucking involves a sudden perturbation of some small section of a string; the subsequent string vibrations can be represented as a straightforward source-filter model. Bowing is a more complex operation. Friction allows the bow to drag the string along horizontally (in the plane of the strings); when the restoring force of string tension becomes large enough, the string snaps back to its quiescent state, only to be again captured by the bow. ...