Electric and Electronic Instruments

Canadian singer-songwriter Lights sings and plays a Roland RD-300GW keyboard synthesizer on stage. In the background there is a drum set and a metal strut forming part of the stage structure. Canadian singer-songwriter Lights performs in Ancaster, Ontario in 2012.
(Shandi-lee Cox | CC BY-NC-ND 2.0)

At the beginning of the 20th century, the construction of power grids caused electrical appliances to become more commonplace, and instrument manufacturers began experimenting with using electricity to create new types of musical instruments.

Electric Instruments

Electric instruments produce sound by translating vibrations into electrical impulses, which are then amplified and played through a speaker.

Electromagnetism

Electric instruments rely on a physical phenomenon called electromagnetism: the ways in which magnetism and electricity interact.

When a magnetic field moves near a conductive wire, it causes the movement of electrons in that wire. This movement of electrons is called a current. Similarly, when a current is run through a wire — for example, by connecting it to a battery — the current creates a magnetic field around the wire.

Figure 1: The motion of a magnetic field around and within a coiled wire — called a solenoid — causes current to flow in the wire. In this diagram, the magnet can be moved with the mouse or left and right arrow keys. Note that the speed of the magnet's motion affects the strength of the current.

This property can be harnessed in a useful way by configuring coiled wires on a rotor inside a magnet-lined housing so that running a current through the wires causes the rotor to spin. This mechanism, called an electric motor, is used to spin discs inside the resonance tubes of a vibraphone, creating a vibrato which gives the instrument its name.

A photograph of a vibraphone with two low keys lifted and laid to the side, revealing the tops of the resonance tubes beneath. Inside the top of the resonance tubes are metal discs which are attached to an axle that bisects the row of tubes.
Figure 2: A vibraphone showing the discs inside the resonance tubes. The discs are mounted on an axle which is attached to a small variable-speed motor. By controlling the speed of the motor, the vibraphonist can change the speed of the instrument's characteristic vibrato.
(Adapted from TPvibes | Pubic Domain)

Microphones and speakers

Simple electromagnetism also forms the foundation of speakers and dynamic microphones. In their most basic form, these devices use a diaphragm attached to a wire coil which is placed within a magnetic housing. When configured as a dynamic microphone, sound waves move the diaphragm and the resulting movement of the coil within the magnetic field creates a variable current in the wire.

When reversed, the same apparatus becomes a speaker; when a rapidly changing current sent through the wire will cause the diaphragm to vibrate, vibrating the air around it and generating sound waves.

A diagram showing a simple public address system. On the left, soundwaves approach a large shape representing a microphone. Inside the microphone is a flat diaphragm attached to a protrusion wrapped with coiled wire. The protrusion sits inside the hole of a doughnut-shaped magnet. Wires connected to the coil feed through a rectangle representing an amplifier. On the right side, the wires connect to the same diaphragm-magnet-coil assembly in mirror image, shown inside a large shape representing a speaker, and soundwaves are shown emanating from the speaker.
Figure 3: A simple public address system. Waves of sound cause a microphone's diaphragm to move. The diaphragm is attached to a coiled wire which, when moved inside a hollow magnet, cause a current in the wire as shown in Figure 1. The current is amplified with a separate amplifier and sent to a speaker. Inside the speaker, the changes in current cause the diaphragm assembly to move inside the magnet, which vibrates the air to create sound.

Actual speakers and microphones refine this process in specific ways to maximize efficiency and fidelity, and other types of microphones — electret microphones and ribbon microphones, for example — use slightly different arrangements to capture sound waves. While theoretically, a simple microphone connected to a simple speaker should work without additional power, in reality the amount of current generated by a microphone is not enough to generate audible sound, so public address systems require the use of an amplifier.

Electric Guitars

In the 1920s and 1930s, acoustic guitar makers began experimenting with electromagnetic processes, eventually creating the modern electric guitar. Rather than using a diaphragm, electric guitars place electromagnetic pickups underneath each metal string. Each pickup consists of a wire coiled around a magnet, so the vibrating string causes fluctuations in the magnet's field which are translated to the wire as a current.

A close-up photograph of an electric guitar, showing two sets of pickups underneath the strings. The flat ends of the cylidrical metal pickups are set flush with the surface of black metal housing; ends of the pickups themselves have slight concentric circular ridges. In the photograph, the second string is blurred, having just been plucked.
Figure 5: Two rows of pickups on an electric guitar. When the guitar's strings vibrate, like the A string in this photo, the variations in the magnetic field create current in the wires coiled around the guitar's pickups.
(Earl Sod | CC BY-NC-ND-2.0)

Because they have a solid body instead of a resonating chamber, electric guitars must be connected to an amplifier for performance; playing an unamplified guitar produces a very quiet acoustic sound.

Hammond organs

Created as a low-cost alternative to the pipe organ, a Hammond organ uses a variation on electric guitar pickups to generate sound. In place of a vibrating string, the Hammond organ uses tonewheels: spinning discs with specially-ridged edges which, when placed next to a pickup, induce a similar current.

A diagram of a tonewheel and pickup. The tonewheel is a gear-like object with many teeth. It is placed next to a pickup: a magnet which has a pointed end. Wires are coiled around the magnet to transmit the induced current.
Figure 7: A tonewheel like those found in many Hammond organs. When the metal wheel spins, the uneven edges cause regular variations in the magnetic field around the pickup, which is delivered as current to an amplifier.

Some models of Hammond organ have a built-in amplifier and speaker, and others must be connected to an external speaker cabinet. They are often used with a Leslie speaker, an amplified speaker which rotates inside its cabinet,creating a vibrato effect which can be controlled by setting the rotational speed.

A photograph of Art Neville playing a Hammond organ and singing into a microphone on an outdoor stage. The organ console is flanked on the right by large speakers and on the left by a white synthesizer keyboard. Behind Neville is a taller cabinet with a wood grain finish that matches the Hammond organ.
Figure 8: American keyboardist Art Neville performs in Savannah, Georgia in 2007. The large cabinet behind Neville is a Leslie speaker, presumably attached to the Hammond organ console in the foreground.
(Bruce Tuten | CC BY-2.0)

Other Electric Instruments

Another method of using electricity to create sound by generating two different frequencies and controlling how they interfere with one another, a process called heterodyning.

The ondes Martenot is an instrument designed around this technique, invented by French cellist and inventor Maurice Martenot after noticing the audible interference created by adjacent radio transmitters. The instrument consists of a specific type of speaker called a diffuseur connected to a console with two control surfaces: a traditional keyboard and a ring suspended from a wire which can be moved from side to side to control the pitch of the instrument's single voice.

A photograph of the keyboard console of an ondes Martenot sitting on an stage. No one is seated at the console, but photocopied pages of sheet music sit on the stand, held in place by colorful clothespins. The rear of the ondes' speaker is seen in front of the console.
Figure 9: The ondes Martenot of ondist Thomas Bloch sits on an outdoor stage in Mittersheim, France before a performance.
(Fredamas | CC BY-SA-4.0)

An instrument which uses a similar principle is the theremin: an electric instrument with which pitch and volume are controlled by moving one's hands near — but not touching — the instrument's two separate antennas.

Figure 10: German-Sorbian thereminist and singer Carolina Eyck performing her arrangement of The Ecstacy of Gold by Italian composer Ennio Morricone from the 1966 film The Good, the Bad, and the Ugly. Eyck performs the piece using a pedal-controlled digital audio workstation which records and loops passages as she performs.

Electronic Instruments

In the field of engineering, electric devices are those which convert electricity to other forms of energy like movement, heat, light, or sound; electronic devices use electricity as a means of conveying and manipulating information. Because all instruments produce sound, musicians generally use the term electronic instrument to refer to an instrument which generates sound computationally rather than through physical vibrations or field interference.

Oscillators

An oscillator is an electronic component which converts a direct current — a current flowing continuously in one direction — into a periodically alternating current. Oscillators can be used to generate AC power, but are more commonly used to create a low-power signal. Oscillators which produce audible frequencies — for example, 440 Hz for A4 — can be used to generate sound in electronic musical instruments.

Oscillators can be constructed in different ways. Early oscillators used vacuum tubes, sealed low-pressure glass containers with electrical components inside. Modern oscillators are generally manufactured as discrete electrical components designed for use on circuit boards.

A close-up photograph of an oscillator component. Seen from above, the component is a shiny metal unit with a top cover that looks like an up-turned miniature cakepan. On the top of the component is the label `BOMAR 27.000MHz VCXO`.
Figure 11: An oscillator component. This specific unit oscillates at 27MHz, a frequency generally used by CB radio.
(Mister rf | CC BY-SA-4.0)

Synthesizers

Any musical instrument which creates sound using oscillators is called a synthesizer. Physical synthesizers are commonly designed one of two configurations.

  • A keyboard synthesizer is a synthesizer with its own built-in keyboard. These instruments may have an on-board amplifier and speakers for standalone use, or may need to be connected an external sound system.
  • A console synthesizer is a component — often designed to be mounted in a standard 19-inch rack — which is meant to be controlled by external input devices and connected to an external sound system. These are often designed to be used with MIDI controllers or computers.

Software synthesizers are computer programs which emulate the sound — and often the physical interface — of physical synthesizers. These programs are generally available as plugins for digital audio workstations.

MIDI

While synthesizers create an audio signal which must be sent to a sound system, most synthesizers are also designed to be controlled by other devices such as keyboards or computers. The language most commonly used to send performance information is called Musical Instrument Digital Interface or MIDI.

A MIDI signal does not contain actual audio waveforms, but instead consists of simple directions, such as a signal to begin playing the note Ab3 at 72% volume. Thus, a set of MIDI directions sent to different synthesizers might yield different results, just as the performance of a certain piece of sheet music will sound different when performed by an oboist, violist, or timpanist.

A MIDI controller is a device which converts a musician's gestures into MIDI information. MIDI controllers do not create sound on their own, just as typing on a computer keyboard has no effect unless it is connected to a computer. MIDI controllers exist in many forms:

  • Keyboard controllers are the most common type of MIDI controller. They are available in many sizes, from full 88-key varieties to more portable 2-octave configurations with miniaturized keys. Keys may be touch-sensitive, detecting the velocity with which the performer presses them and sending it as a MIDI signal, and more expensive models may feature weighted keys to better mimic the feel of an acoustic piano. Most controllers support the use of a sustain pedal and include a pitch bend wheel for controlling the tuning of individual notes, and other wheels, buttons, or sliders which can be programmed to send other types of MIDI data.
  • Wind controllers are controllers which are played like wind instruments. They feature keys which can be configured to match fingering systems of instruments like flute, saxophone or clarinet or which mimic the valves of a trumpet, euphonium or tuba, and a breath controller which detects the intensity of the air being pushed through the instrument by the player.
    • A photograph of two wind controllers, an Akai EWI 3020 and a Yamaha WX5, laying on a leather cushion. Both have plastic bodies; the Yamaha instrument has sixteen visible keys in a lever configuration while the Akai instrument has thirteen touch-senstitive metal discs.
    Figure 14: Two wind controllers: a Yamaha WX5 and an Akai EWI 3020.
    (Jon Delorey | CC BY-NC-2.0)
  • Drum set controllers are systems of various separate controllers configured to match a standard drum set, including pressure-sensitive pads for snare drums, toms, and cymbals, and pedal controllers for bass drum and hi-hat.
  • Other types of MIDI controllers include keytars which provide a keyboard in a guitar-like configuration, mallet controllers which have a xylophone-like playing surface, string controllers which take the shape or guitars, violins or other string instruments, and other sensors which detect movement, light or sound.

MIDI interfaces allow computers to be connected to a MIDI system. Connected controllers can be used to provide input for music software such as scorewriters, digital audio workstations, and others. These programs can also be configured to control external synthesizers and other MIDI-compatible equipment such as lighting systems and pyrotechnics.

Figure 15: Computers can read MIDI messages when MIDI devices are connected using a MIDI interface. In compatible browsers, activity on any connected MIDI device should be displayed here.

While late-20th century MIDI setups often relied on external equipment and complicated cabling, modern electronic musicians tend to only use software-based synthesizers. As a result, modern setups often include a MIDI keyboard controller with a built-in MIDI interface connected to a desktop or laptop computer with a single USB cable.

Electric and Electronic Instruments: Summary

  • Electric Instruments produce sound by translating vibrations into electrical impulses to be sent to a speaker.
    • The electromagnetic force causes a current to move through a wire when a magnetic field moves nearby.
    • Similarly, a current is sent through a wire creates a magnetic field around the wire.
  • Microphones use this concept to translate sound waves into electrical current, and speakers use it to translate electrical current into sound waves.
  • Electric guitars use electromagnetic pickups beneath each string to convert the string's vibrations into electrical current.
  • Hammond organs use tonewheels placed near pickups to generate an electromagnetic signal.
    • Hammond organs are often used with Leslie speakers, which are speakers placed on rotating platforms to create vibrato.
  • Electric instruments like the ondes Martenot and theremin use the interference of radio transmitters set to different frequencies.
  • Electronic instruments generate sound computationally rather than through physical vibrations or interference.
  • Synthesizers create sound with oscillators, which are electrical components that convert direct current into alternating current.
    • Keyboard synthesizers are synthesizers with built-in keyboards.
    • Console synthesizers are synthesizers which are usually mounted in a cabinet, and are controller by a separate keyboard or computer system.
    • Software synthesizers are computer programs which emulate the sound and interface of physical synthesizers.
  • MIDI, which stands for Musical Instrument Digital Interface, is a language used by electronic instruments and controllers to communicate.
    • MIDI signals consist of instructions for playback, not recordings of the sound itself.
    • MIDI controllers are devices which translate human performance into MIDI signals, and include keyboard controllers, wind controllers, drum set controllers, and others.
    • MIDI interfaces allow MIDI devices to be connected to computers, allowing for software programs like scorewriters and digital audio workstations to read and control MIDI devices.

Exercises

Exercise 1: Classifying Instruments

Next: Synthesis