To prepare for this, we need to consider how such instruments work. A structure is resonant if it responds to an energy impulse by vibrating for a noticeable length of time. The frequency of vibration is determined by the size and material of the resonator, and the pattern of vibration may be simple harmonic motion or some more complex action. A repeating series of impulses will sustain the vibrations if the frequency of the pulses matches to some degree the natural frequencies of the resonator. A simple instrument Most instruments also possess some kind of pitch control mechanism.
Pitch is controlled at two levels, tuning and performance.
The tuning of an instrument determines the pitch possibilities that the artist may exploit during the performance. An instrument's tuning is largely in the manufacturing process, although there is often some provision made for adjustments. Pitch controllers may modify the operation of the resonator, the driver, or both. Some instruments provide pitch selection by duplication of tuned structures, trading flexibility of intonation for the possibility of polyphonic performance. The driver or sound generation device of the string instrument is a tightly stretched string.