TABLE OF CONTENTS Defining the timbre of an instrument is no simple task. The literature on the subject is as abundant as it is diverse, with such important works in the 20 th century as the Trait des objets musicaux [SCH 66] by P. Schaeffer ( A treatise on musical objects). In this chapter, we will simply write down and describe two characteristics that allow (sometimes not completely) to tell different instruments apart:
the nature of the sound's spectrum, which depends on the one hand on the vibrator (string, reed, bar, membrane), and on the other on the resonator (sounding board, pipe) which will amplify and 'give color' to the sound produced;
the sound's envelope, which defines the way a given musical sound is born, lives and dies.
Many other elements have to be considered, such as the vibrato, the intensity of the air flow for wind instruments or the initial impact for percussion instruments, the reverberation of the other strings in a piano, or also the phase shift (Doppler effect, Leslie effect) used for example by jazz musicians by moving around or spinning their instruments. Viola players also share this strange custom, sometimes making their audience seasick! We will discuss some of these aspects in Chapter 6.
Music instruments produce sounds that basically have a discrete spectrum. Hence these sounds can be expressed as
an approximation valid at least over a relatively short interval of time. As a result,...
