It is difficult to organize a general discussion of operating principlesof instruments because there are so many varieties, but for engineering purposeswe can divide instruments into three classes based on the style of driver thefamiliar strings, winds, and percussion instruments. Some instrumentsprovide pitch selection by duplication of tuned structures, trading flexibilityof intonation for the possibility of polyphonic performance. Pitch controllersmay modify the operation of the resonator, the driver, or both. An instrument's tuning is largely in the manufacturing process,although there is often some provision made for adjustments.
The tuning of aninstrument determines the pitch possibilities that the artist may exploit duringthe performance. Most instruments also possess some kind of pitch control mechanism.Pitch is controlled at two levels, tuning and performance. Ifthe driver supplies the energy all at once, it is an IMPULSE driver if theenergy is applied as a repeated stream of pushes, the driver is often called aSOUND GENERATOR.
The driver may be as simple asa stick (or bare hand), or it may be an elaborate resonant structure itself. If the input frequency has to match thefrequency of the resonator pretty closely before resonance occurs, the resonatoris NARROWLY TUNED.Īcoustic instruments also require some sort of DRIVER, a mechanism that appliesenergy to the resonator in the appropriate form. If the resonator responds to a wide range of inputfrequency, it is BROADLY TUNED.
A repeating series of impulses will sustain thevibrations if the frequency of the pulses matches to some degree the naturalfrequencies of the resonator. If the vibration dies away quickly, theresonator is said to be DAMPED. The frequency of vibration is determined by the size andmaterial of the resonator, and the pattern of vibration may be simple harmonicmotion or some more complex action. A structureis resonant if it responds to an energy impulse by vibrating for a noticeablelength of time. Acoustic Instruments A LOOK AT UN-ELECTRONIC MUSICAL INSTRUMENTSĪ little later in the course we will be looking at the problem of how toconstruct an electrical model, or analog, of an acoustical musical instrument.To prepare for this, we need to consider how such instruments work.Īll acoustical instruments are built around some kind of RESONATOR.
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