Guitar amplifier in the context of "Effects unit"

The guitar is a stringed musical instrument that is usually fretted (with some exceptions) and typically has six or twelve strings. It is usually held flat against the player's body and played by strumming or plucking the strings with the dominant hand, while simultaneously pressing selected strings against frets with the fingers of the opposite hand. A guitar pick may also be used to strike the strings. The sound of the guitar is projected either acoustically, by means of a resonant hollow chamber on the guitar, or amplified by an electronic pickup and an amplifier.

The guitar is classified as a chordophone, meaning the sound is produced by a vibrating string stretched between two fixed points. Historically, a guitar was constructed from wood, with its strings made of catgut. Steel guitar strings were introduced near the end of the nineteenth century in the United States, but nylon and steel strings became mainstream only following World War II. The guitar's ancestors include the gittern, the vihuela, the four-course Renaissance guitar, and the five-course baroque guitar, all of which contributed to the development of the modern six-string instrument.

Alternating current (AC) is an electric current that periodically reverses direction and changes its magnitude continuously with time, in contrast to direct current (DC), which flows only in one direction. Alternating current is the form in which electric power is delivered to businesses and residences, and it is the form of electrical energy that consumers typically use when they plug kitchen appliances, televisions, fans and electric lamps into a wall socket. The abbreviations AC and DC are often used to mean simply alternating and direct, respectively, as when they modify current or voltage.

The usual waveform of alternating current in most electric power circuits is a sine wave, whose positive half-period corresponds with positive direction of the current and vice versa (the full period is called a cycle). "Alternating current" most commonly refers to power distribution, but a wide range of other applications are technically alternating current although it is less common to describe them by that term. In many applications, like guitar amplifiers, different waveforms are used, such as triangular waves or square waves. Audio and radio signals carried on electrical wires are also examples of alternating current. These types of alternating current carry information such as sound (audio) or images (video) sometimes carried by modulation of an AC carrier signal. These currents typically alternate at higher frequencies than those used in power transmission.

Distortion and overdrive are forms of audio signal processing used to alter the sound of amplified electric musical instruments, usually by increasing their gain, producing a "fuzzy", "growling", or "gritty" tone. Distortion is most commonly used with the electric guitar, but may be used with other instruments, such as electric bass, electric piano, synthesizer, and Hammond organ. Guitarists playing electric blues originally obtained an overdriven sound by turning up their vacuum tube-powered guitar amplifiers to high volumes, which caused the signal to distort. Other ways to produce distortion have been developed since the 1960s, such as distortion effect pedals. The growling tone of a distorted electric guitar is a key part of many genres, including blues and many rock music genres, notably hard rock, punk rock, hardcore punk, acid rock, grunge and heavy metal music, while the use of distorted bass has been essential in a genre of hip hop music and alternative hip hop known as "SoundCloud rap".

The effects alter the instrument sound by clipping the signal (pushing it past its maximum, which shears off the peaks and troughs of the signal waves), adding sustain and harmonic and inharmonic overtones and leading to a compressed sound that is often described as "warm" and "dirty", depending on the type and intensity of distortion used. The terms distortion and overdrive are often used interchangeably; where a distinction is made, distortion is a more extreme version of the effect than overdrive. Fuzz is a particular form of extreme distortion originally created by guitarists using faulty equipment (such as a misaligned valve (tube); see below), which has been emulated since the 1960s by a number of "fuzzbox" effects pedals.

Jazz fusion (also known as jazz rock, jazz-rock fusion, or simply fusion) is a popular music genre that developed in the late 1960s when musicians combined jazz harmony and improvisation with rock music, funk, and rhythm and blues. Electric guitars and basses, amplifiers, and keyboard instruments (including electric pianos and organs) that were popular in rock began to be used by jazz musicians, particularly those who had grown up listening to rock and roll.

Jazz fusion arrangements vary in complexity. Some employ groove-based vamps fixed to a single key or a single chord with a simple, repeated melody. Others use elaborate chord progressions, unconventional time signatures, or melodies with counter-melodies, in a similar fashion to progressive rock. These arrangements, whether simple or complex, typically include improvised sections that can vary in length, much like in other forms of jazz.

An electric guitar is a guitar that requires external electric sound amplification in order to be heard at typical performance volumes, unlike a standard acoustic guitar. It uses one or more pickups to convert the vibration of its strings into electrical signals, which ultimately are reproduced as sound by loudspeakers. The sound is sometimes shaped or electronically altered to achieve different timbres or tonal qualities via amplifier settings or knobs on the guitar. Often, this is done through the use of effects such as reverb, distortion and "overdrive"; the latter is considered to be a key element of electric blues guitar music and jazz, rock and heavy metal guitar playing. Designs also exist combining attributes of electric and acoustic guitars: the semi-acoustic and acoustic-electric guitars.

Invented in 1932, the electric guitar was adopted by jazz guitar players, who wanted to play single-note guitar solos in large big band ensembles. Early proponents of the electric guitar on record include Les Paul, Eddie Durham, George Barnes, Lonnie Johnson, Sister Rosetta Tharpe, T-Bone Walker, and Charlie Christian. During the 1950s and 1960s, the electric guitar became the most important instrument in popular music. It has evolved into an instrument that is capable of a multitude of sounds and styles in genres ranging from pop and rock to folk to country music, blues and jazz. It served as a major component in the development of electric blues, rock and roll, rock music, heavy metal music and many other genres of music.

An audio power amplifier (or power amp) amplifies low-power electronic audio signals, such as the signal from a radio receiver or an electric guitar pickup, to a level that is high enough for driving loudspeakers or headphones. Audio power amplifiers are found in all manner of sound systems including sound reinforcement, public address, home audio systems and musical instrument amplifiers like guitar amplifiers. It is the final electronic stage in a typical audio playback chain before the signal is sent to the loudspeakers.

The preceding stages in such a chain are low-power audio amplifiers which perform tasks like pre-amplification of the signal, equalization, mixing different input signals. The inputs can also be any number of audio sources like record players, CD players, digital audio players and cassette players. Most audio power amplifiers require these low-level inputs, which are line level.

An electric piano is a musical instrument that has a piano-style musical keyboard, where sound is produced by means of mechanical hammers striking metal strings or reeds or wire tines, which leads to vibrations which are then converted into electrical signals by pickups (either magnetic, electrostatic, or piezoelectric). The pickups are connected to an instrument amplifier and loudspeaker to reinforce the sound sufficiently for the performer and audience to hear. Unlike a synthesizer, the electric piano is not an electronic instrument. Instead, it is an electro-mechanical instrument. Some early electric pianos used lengths of wire to produce the tone, like a traditional piano. Smaller electric pianos used short slivers of steel to produce the tone (a lamellophone with a keyboard & pickups). The earliest electric pianos were invented in the late 1920s; the 1929 Neo-Bechstein electric grand piano was among the first. Probably the earliest stringless model was Lloyd Loar's Vivi-Tone Clavier. A few other noteworthy producers of electric pianos include Baldwin Piano and Organ Company, and the Wurlitzer Company.

Early electric piano recordings include Duke Ellington's in 1955 and Sun Ra's India as well as other tracks from the 1956 sessions included on his second album Super Sonic Jazz (a.k.a. Super Sonic Sounds). The popularity of the electric piano began to grow in the late 1950s after Ray Charles's 1959 hit record "What'd I Say", reaching its height during the 1970s, after which they were progressively displaced by more lightweight electronic pianos capable of piano-like sounds without the disadvantages of electric pianos' heavy weight and moving mechanical parts. Another factor driving their development and acceptance was the progressive electrification of popular music and the need for a portable keyboard instrument capable of high-volume amplification. Musicians adopted a number of types of domestic electric pianos for rock and pop use. This encouraged their manufacturers to modify them for stage use and then develop models primarily intended for stage use.

Jazz guitar may refer to either a type of electric guitar or a guitar playing style in jazz, using electric amplification to increase the volume of acoustic guitars.

In the early 1930s, jazz musicians sought to amplify their sound to be heard over loud big bands. When guitarists in big bands switched from acoustic to semi-acoustic guitar and began using amplifiers, it enabled them to play solos. Jazz guitar had an important influence on jazz in the beginning of the twentieth century. Although the earliest guitars used in jazz were acoustic and acoustic guitars are still sometimes used in jazz, most jazz guitarists since the 1940s have performed on an electrically amplified guitar or electric guitar.