Electronic Musical Instruments

musical instruments in which a generator of one kind or another produces electric oscillations, controlled by the performer, that activate a loudspeaker. Also classified as electronic instruments are ordinary instruments the mechanical oscillations of whose vibrators (for example, the strings of an electric guitar) are converted into electric oscillations with the aid of a pickup. Electronic instruments are used primarily in variety-stage ensembles.

Some electronic instruments use oscillators whose frequency can be varied over a continuous range. The performer determines the precise pitch of each sound, which he can alter smoothly by sliding a finger along a special neck with graduations or, as in the theremin, the first instrument of this type, by moving his hand in front of a special antenna. Instruments in this category are monophonic or, more rarely, duophonic. Their advantage lies in the ability to perform melodies in a very expressive manner; their drawback is low pitch stability.

Other electronic instruments, usually polyphonic keyboard instruments, have a number of oscillators, each operating at a given frequency; these are fixed-pitch instruments. In addition to electronic generators, such instruments may also use mechanical generators with notched wheels that rotate in close proximity to electromagnets. Some instruments of this type use photoelectric generators that direct a beam of light onto a photoelectric cell; when the beam is interrupted or fluctuates in intensity, the ensuing oscillations are translated into musical sounds. Volume is generally controlled by means of a pedal. Electronic instruments are equipped with special devices that allow the performer to impart a variety of musical characteristics to the tone, such as soft attack and decrescendo (the gradual building up and fading away of the tone), and legato (the smooth passage from one tone to another).

Timbre may be achieved in two ways. In one approach the relationships between the amplitudes of the various harmonic overtones are held constant. In order to maintain this fixed relationship, it is necessary to select, for example, some form of vibration curve that varies for tones of different pitches only in its duration and for tones of different volumes only in its amplitude. It is also possible to synthesize a timbre by mixing the oscillations of the fundamental frequency with oscillations that are produced by generators belonging to the same instrument and that correspond to the various harmonic overtones.

The second means of creating timbre is to introduce resonant circuits (filters) that amplify the overtones of the generated oscillations in a certain frequency range—the formant. The construction of the different instruments makes it possible to create in each a range of timbres that the musician can alter in the course of his performance. In order to imitate the vibration of the human voice and the vibrato of stringed instruments, the pitch of a tone is modified by a frequency change of 5–6 hertz. The popping noises that occur when a tone is abruptly turned on or off are damped either by a volume regulator (pedal) or by special devices that regulate transients in the generators.