These may be divided into two main categories: original electronic instruments and electronic versions of acoustic instruments.
Original electronic instruments
The most familiar electronic instruments today are synthesizers. These contain banks of sounds which are either created artificially from sine waves, noise, or (increasingly) short samples of acoustic instruments. Synthesizers may be controlled by computer, or may themselves act as keyboard controllers for other instruments, such as samplers. The enormous range and variety of timbres available on modern synthesizers make them probably the most versatile instrument in existence.
The creation of original electronic instruments has a long history, beginning with mechanical devices such as the player piano or Percy Grainger's early experiments in substituting conductors with "orchestral supervisors" operating mechanical music stands. At the turn of the 20th century, William Duddell invented the Singing Arc, made of a series of arc lamps controlled via a keyboard. In 1913, Luigi Russolo created Intonarumori, or noise instruments. Other early instruments included the Telharmonium (which transmitted electric sounds down telephone wires) and the Trautonium. A detailed account of these and many other early electronic instruments may be found here. Two of these early instruments which have achieved a lasting place in concert music are the Theremin and the Ondes Martenot.
The Theremin was invented in 1920 by Leon Thérémin (he originally called it 'the aetherophone') and has a distinctive quavering electronic sound controlled by hand motion around a central rod.
The Ondes Martenot was first called the 'ondes musicales' by its inventor Maurice Martenot in 1928. It has been used extensively by French composers, in particular Olivier Messiaen.
Electronic versions of acoustic instruments
The range of electronically modified or simulated instruments is vast, from the very familiar electric guitars through to modified clarinets and tubas. Electric keyboards deserve a special mention, in particular organs (the Wurlitzer, for example, was invented in 1946) and electric pianos. The latter include amplified pianos and sampled pianos, but also a number of instruments that have achieved a distinctive character by electronically generating sound. The Fender Rhodes piano is probably the most celebrated of these.
Most contemporary developments, however, use digital technologies to extend and develop instrumental possibilities. STEIM (the Studio for Electro-Instrumental Music) is a good site to visit to build up a picture of the current range of possibilities. Instruments may be used as controllers for other sound events, or the sounds produced by the instruments might be modified in various ways by the players. The full potential of all these developments has yet to be realised in orchestral concert music.
The Orchestra: A User's Manual is a free resource and will remain so. It still receives between 8,000 and 16,000 unique visits per month from all over the world. See the testimonials. Thanks to all the donations, I have been able to create this responsive re-design. But the movies and sound clips recorded in 2004 do show their age. I would really like to re-record everything and add many more techniques, especially for solo and ensemble writing. I estimate this will cost around £30,000. If you know a source of such funds, please contact me: a.hugill [at] bathspa.ac.uk