Overdrive (music)
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Distortion and overdrive are forms of
audio signal processing Audio signal processing is a subfield of signal processing that is concerned with the electronic manipulation of audio signals. Audio signals are electronic representations of sound waves— longitudinal waves which travel through air, consist ...
used to alter the sound of amplified electric musical instruments, usually by increasing their
gain Gain or GAIN may refer to: Science and technology * Gain (electronics), an electronics and signal processing term * Antenna gain * Gain (laser), the amplification involved in laser emission * Gain (projection screens) * Information gain in d ...
, producing a "fuzzy", "growling", or "gritty" tone. Distortion is most commonly used with the
electric guitar An electric guitar is a guitar that requires external amplification in order to be heard at typical performance volumes, unlike a standard acoustic guitar (however combinations of the two - a semi-acoustic guitar and an electric acoustic gu ...
, but may also be used with other electric instruments such as
electric bass The bass guitar, electric bass or simply bass (), is the lowest-pitched member of the string family. It is a plucked string instrument similar in appearance and construction to an electric or an acoustic guitar, but with a longer neck and ...
,
electric piano An electric piano is a musical instrument which produces sounds when a performer presses the keys of a piano-style musical keyboard. Pressing keys causes mechanical hammers to strike metal strings, metal reeds or wire tines, leading to vibrations ...
,
synthesizer A synthesizer (also spelled synthesiser) is an electronic musical instrument that generates audio signals. Synthesizers typically create sounds by generating waveforms through methods including subtractive synthesis, additive synthesis ...
and
Hammond organ The Hammond organ is an electric organ invented by Laurens Hammond and John M. Hanert and first manufactured in 1935. Multiple models have been produced, most of which use sliding #Drawbars, drawbars to vary sounds. Until 1975, Hammond organs ...
. Guitarists playing
electric blues Electric blues refers to any type of blues music distinguished by the use of electric amplification for musical instruments. The guitar was the first instrument to be popularly amplified and used by early pioneers T-Bone Walker in the late 19 ...
originally obtained an overdriven sound by turning up their
vacuum tube A vacuum tube, electron tube, valve (British usage), or tube (North America), is a device that controls electric current flow in a high vacuum between electrodes to which an electric voltage, potential difference has been applied. The type kn ...
-powered
guitar amplifier A guitar amplifier (or amp) is an electronic device or system that strengthens the electrical signal from a pickup on an electric guitar, bass guitar, or acoustic guitar so that it can produce sound through one or more loudspeakers, which a ...
s to high volumes, which caused the signal to distort. While overdriven tube amps are still used to obtain overdrive, especially in genres like blues and
rockabilly Rockabilly is one of the earliest styles of rock and roll music. It dates back to the early 1950s in the United States, especially the Southern United States, South. As a genre it blends the sound of Western music (North America), Western music ...
, a number of other ways to produce distortion have been developed since the 1960s, such as distortion
effect pedals An effects unit or effects pedal is an electronic device that alters the sound of a musical instrument or other audio source through audio signal processing. Common effects include distortion/overdrive, often used with electric guitar in el ...
. The growling tone of a distorted electric guitar is a key part of many genres, including blues and many
rock music Rock music is a broad genre of popular music that originated as "rock and roll" in the United States in the late 1940s and early 1950s, developing into a range of different styles in the mid-1960s and later, particularly in the United States and ...
genres, notably hard rock, punk rock,
hardcore punk Hardcore punk (also known as simply hardcore) is a punk rock music genre and subculture that originated in the late 1970s. It is generally faster, harder, and more aggressive than other forms of punk rock. Its roots can be traced to earlier pu ...
, acid rock, 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. Distortion, overdrive, and fuzz can be produced by
effects pedals An effects unit or effects pedal is an electronic device that alters the sound of a musical instrument or other audio source through audio signal processing. Common effects include distortion/overdrive, often used with electric guitar in ...
, rackmounts,
pre-amplifier A preamplifier, also known as a preamp, is an electronic amplifier that converts a weak electrical signal into an output signal strong enough to be noise-tolerant and strong enough for further processing, or for sending to a power amplifier ...
s, power amplifiers (a potentially speaker-blowing approach), speakers and (since the 2000s) by digital amplifier modeling devices and audio software.Aikin, Jim (2004)
''Power Tools for Synthesizer Programming''
Hal Leonard. p. 171.
These effects are used with
electric guitar An electric guitar is a guitar that requires external amplification in order to be heard at typical performance volumes, unlike a standard acoustic guitar (however combinations of the two - a semi-acoustic guitar and an electric acoustic gu ...
s,
electric bass The bass guitar, electric bass or simply bass (), is the lowest-pitched member of the string family. It is a plucked string instrument similar in appearance and construction to an electric or an acoustic guitar, but with a longer neck and ...
es ( fuzz bass),
electronic keyboard An electronic keyboard, portable keyboard, or digital keyboard is an electronic musical instrument, an electronic derivative of keyboard instruments. Electronic keyboards include synthesizers, digital pianos, stage pianos, electronic organs ...
s, and more rarely as a special effect with vocals. While distortion is often created intentionally as a musical effect, musicians and sound engineers sometimes take steps to avoid distortion, particularly when using
PA system A public address system (or PA system) is an electronic system comprising microphones, amplifiers, loudspeakers, and related equipment. It increases the apparent volume (loudness) of a human voice, musical instrument, or other acoustic sound sou ...
s to amplify vocals or when playing back prerecorded music.


History


Early uses of amplified distortion

The first guitar amplifiers were relatively low-fidelity, and would often produce distortion when their volume (
gain Gain or GAIN may refer to: Science and technology * Gain (electronics), an electronics and signal processing term * Antenna gain * Gain (laser), the amplification involved in laser emission * Gain (projection screens) * Information gain in d ...
) was increased beyond their design limit or if they sustained minor damage. Around 1945, Western-swing guitarist Junior Barnard began experimenting with a rudimentary humbucker pick-up and a small amplifier to obtain his signature "low-down and dirty" bluesy sound. Many
electric blues Electric blues refers to any type of blues music distinguished by the use of electric amplification for musical instruments. The guitar was the first instrument to be popularly amplified and used by early pioneers T-Bone Walker in the late 19 ...
guitarists, including Chicago bluesmen such as
Elmore James Elmore James ( Brooks; January 27, 1918 – May 24, 1963) was an American blues guitarist, singer, songwriter, and bandleader. Noted for his use of loud amplification and his stirring voice, James was inducted into the Rock and Roll Hall of Fa ...
and Buddy Guy, experimented in order to get a guitar sound that paralleled the rawness of blues singers such as
Muddy Waters McKinley Morganfield (April 4, 1913 April 30, 1983), known professionally as Muddy Waters, was an American blues singer and musician who was an important figure in the post- war blues scene, and is often cited as the "father of modern Chicag ...
and
Howlin' Wolf Chester Arthur Burnett (June 10, 1910January 10, 1976), better known by his stage name Howlin' Wolf, was an American blues singer and guitarist. He is regarded as one of the most influential blues musicians of all time. Over a four-decade car ...
, replacing often their originals with the powerful Valco "Chicagoan" pick-ups, originally created for lap-steel, to obtain a louder and fatter tone. In early
rock music Rock music is a broad genre of popular music that originated as "rock and roll" in the United States in the late 1940s and early 1950s, developing into a range of different styles in the mid-1960s and later, particularly in the United States and ...
, Goree Carter's "Rock Awhile" (1949) featured an over-driven electric guitar style similar to that of Chuck Berry several years later,
Robert Palmer Robert Allen Palmer (19 January 1949 – 26 September 2003) was an English singer and songwriter. He was known for his powerful, soulful voice and wikt:sartorial, sartorial elegance, and his stylistic explorations, combining Soul music, so ...
, "Church of the Sonic Guitar", pp. 13-38 in Anthony DeCurtis, ''Present Tense'',
Duke University Press Duke University Press is an academic publisher and university press affiliated with Duke University. It was founded in 1921 by William T. Laprade as The Trinity College Press. (Duke University was initially called Trinity College). In 1926 Du ...
, 1992, p. 19. .
as well as Joe Hill Louis' " Boogie in the Park" (1950). In the early 1950s, guitar distortion sounds started to evolve based on sounds created earlier in the decade by accidental damage to amps, such as in the popular early recording of the 1951 Ike Turner and the Kings of Rhythm song " Rocket 88", where guitarist Willie Kizart used a vacuum tube amplifier that had a speaker cone slightly damaged in transport. Electric guitarists began intentionally "doctoring" amplifiers and speakers in order to emulate this form of distortion. Electric blues guitarist Willie Johnson of
Howlin' Wolf Chester Arthur Burnett (June 10, 1910January 10, 1976), better known by his stage name Howlin' Wolf, was an American blues singer and guitarist. He is regarded as one of the most influential blues musicians of all time. Over a four-decade car ...
′s band began deliberately increasing gain beyond its intended levels to produce "warm" distorted sounds. Guitar Slim also experimented with distorted overtones, which can be heard in his hit
electric blues Electric blues refers to any type of blues music distinguished by the use of electric amplification for musical instruments. The guitar was the first instrument to be popularly amplified and used by early pioneers T-Bone Walker in the late 19 ...
song " The Things That I Used to Do" (1953).
Chuck Berry Charles Edward Anderson Berry (October 18, 1926 – March 18, 2017) was an American singer, songwriter and guitarist who pioneered rock and roll. Nicknamed the "Honorific nicknames in popular music, Father of Rock and Roll", he refined a ...
's 1955 classic " Maybellene" features a guitar solo with warm overtones created by his small valve amplifier. Pat Hare produced heavily distorted power chords on his electric guitar for records such as James Cotton's "
Cotton Crop Blues Cotton is a soft, fluffy staple fiber that grows in a boll, or protective case, around the seeds of the cotton plants of the genus ''Gossypium'' in the mallow family Malvaceae. The fiber is almost pure cellulose, and can contain minor perce ...
" (1954) as well as his own "I'm Gonna Murder My Baby" (1954), creating "a grittier, nastier, more ferocious electric guitar sound,"
Robert Palmer Robert Allen Palmer (19 January 1949 – 26 September 2003) was an English singer and songwriter. He was known for his powerful, soulful voice and wikt:sartorial, sartorial elegance, and his stylistic explorations, combining Soul music, so ...
, "Church of the Sonic Guitar", pp. 13-38 in Anthony DeCurtis, ''Present Tense'',
Duke University Press Duke University Press is an academic publisher and university press affiliated with Duke University. It was founded in 1921 by William T. Laprade as The Trinity College Press. (Duke University was initially called Trinity College). In 1926 Du ...
, 1992, pp. 24-27. .
accomplished by turning the volume knob on his amplifier "all the way to the right until the speaker was screaming." In 1956, guitarist Paul Burlison of the Johnny Burnette Trio deliberately dislodged a
vacuum tube A vacuum tube, electron tube, valve (British usage), or tube (North America), is a device that controls electric current flow in a high vacuum between electrodes to which an electric voltage, potential difference has been applied. The type kn ...
in his amplifier to record " The Train Kept A-Rollin" after a reviewer raved about the sound Burlison's damaged amplifier produced during a live performance. According to other sources Burlison's amp had a partially broken loudspeaker cone. Pop-oriented producers were horrified by that eerie "two-tone" sound, quite clean on trebles but strongly distorted on basses, but Burnette insisted to publish the sessions, arguing that "that guitar sounds like a nice horn section". In the late 1950s, Guitarist Link Wray began intentionally manipulating his amplifiers' vacuum tubes to create a "noisy" and "dirty" sound for his solos after a similarly accidental discovery. Wray also poked holes in his speaker cones with pencils to further distort his tone, used electronic echo chambers (then usually employed by singers), the recent powerful and "fat" Gibson humbucker pickups, and controlled "feedback" ( Larsen effect). The resultant sound can be heard on his highly influential 1958
instrumental An instrumental is a recording normally without any vocals, although it might include some inarticulate vocals, such as shouted backup vocals in a big band setting. Through semantic widening, a broader sense of the word song may refer to instr ...
, "
Rumble Rumble or Rumbling may refer to: Sounds and vibrations * Rumble (noise), a form of low frequency noise * Rumble, a haptic feedback vibration feature in video game controllers * Rumbling, a quality of a heart murmur * Stomach rumble, or borbory ...
" and Rawhide.


1960s: fuzz, distortion, and introduction of commercial devices

In 1961, Grady Martin scored a hit with a fuzzy tone caused by a faulty preamplifier that distorted his guitar playing on the Marty Robbins song " Don't Worry". Later that year Martin recorded an instrumental tune under his own name, using the same faulty preamp. The song, on the Decca label, was called "The Fuzz." Martin is generally credited as the discoverer of the "fuzz effect." The recording engineer from Martin's sessions, Glenn Snoddy, partnered with fellow WSM radio engineer Revis V. Hobbs to design and build a stand-alone device that would intentionally create the fuzzy effect. The two engineers sold their circuit to Gibson, who introduced it as the Maestro FZ-1 Fuzz-Tone in 1962, one of the first commercially-successful mass-produced guitar pedals. Shortly thereafter, the American instrumental rock band
The Ventures The Ventures are an American instrumental rock band formed in Tacoma, Washington, in 1958, by Don Wilson and Bob Bogle. The band, which was a quartet for most of its existence, helped to popularize the electric guitar across the world during the ...
asked their friend, session musician and electronics enthusiast Orville "Red" Rhodes for help recreating the Grady Martin "fuzz" sound. Rhodes offered The Ventures a fuzzbox he had made, which they used to record "2000 Pound Bee" in 1962. In 1964, a fuzzy and somewhat distorted sound gained widespread popularity after guitarist
Dave Davies David Russell Gordon Davies (born 3 February 1947) is an English guitarist, singer and songwriter. He was the lead guitarist and backing vocalist for the English rock band the Kinks, which also featured his elder brother Ray Davies. He was ...
of
The Kinks The Kinks were an English rock band formed in Muswell Hill, north London, in 1963 by brothers Ray and Dave Davies. They are regarded as one of the most influential rock bands of the 1960s. The band emerged during the height of British rhyt ...
used a razor blade to slash his speaker cones for the band's single "
You Really Got Me "You Really Got Me" is a song written by Ray Davies for English rock band the Kinks. The song, originally performed in a more blues-oriented style, was inspired by artists such as Lead Belly and Big Bill Broonzy. Two versions of the song ...
". In May 1965
Keith Richards Keith Richards (born 18 December 1943), often referred to during the 1960s and 1970s as "Keith Richard", is an English musician and songwriter who has achieved international fame as the co-founder, guitarist, secondary vocalist, and co-princi ...
used a Maestro FZ-1 Fuzz-Tone to record " (I Can't Get No) Satisfaction". The song's success greatly boosted sales of the device, and all available stock sold out by the end of 1965. Other early fuzzboxes include the Mosrite FuzzRITE and Arbiter Group Fuzz Face used by Jimi Hendrix, the
Electro-Harmonix Electro-Harmonix (also commonly referred to as EHX) is a New York City-based company that makes electronic audio processors and sells rebranded vacuum tubes. The company was founded by Mike Matthews in 1968. It is best known for a series of g ...
Big Muff Pi used by Hendrix and
Carlos Santana Carlos Humberto Santana Barragán (; born July 20, 1947) is an American guitarist who rose to fame in the late 1960s and early 1970s with his band Santana, which pioneered a fusion of Rock and roll and Latin American jazz. Its sound feature ...
, and the Vox Tone Bender used by
Paul McCartney Sir James Paul McCartney (born 18 June 1942) is an English singer, songwriter and musician who gained worldwide fame with the Beatles, for whom he played bass guitar and shared primary songwriting and lead vocal duties with John Lennon. On ...
to play fuzz bass on " Think for Yourself" and other Beatles recordings. In 1966, Jim Marshall of the British company
Marshall Amplification Marshall is a British company that designs and manufactures music amplifiers, speaker cabinets, brands personal headphones and earphones, drums and bongos. The company also owns a record label called Marshall Records. It was founded in Lon ...
began modifying the electronic circuitry of his amplifiers so as to achieve a "brighter, louder" sound and fuller distortion capabilities. Also in 1966,
Syd Barrett Roger Keith "Syd" Barrett (6 January 1946 – 7 July 2006) was an English singer, songwriter, and musician who co-founded the rock band Pink Floyd in 1965. Barrett was their original frontman and primary songwriter, becoming known for his ...
of
Pink Floyd Pink Floyd are an English rock band formed in London in 1965. Gaining an early following as one of the first British psychedelic groups, they were distinguished by their extended compositions, sonic experimentation, philosophical lyrics an ...
created the song Interstellar Overdrive, a song made entirely in electric distortion. It was released a year later in modified form on their debut album The Piper at the Gates of Dawn. In the late 1960s and early 1970s hard rock bands such as Deep Purple,
Led Zeppelin Led Zeppelin were an English rock band formed in London in 1968. The group comprised vocalist Robert Plant, guitarist Jimmy Page, bassist/keyboardist John Paul Jones, and drummer John Bonham. With a heavy, guitar-driven sound, they are c ...
and
Black Sabbath Black Sabbath were an English rock band formed in Birmingham in 1968 by guitarist Tony Iommi, drummer Bill Ward, bassist Geezer Butler and vocalist Ozzy Osbourne. They are often cited as pioneers of heavy metal music. The band helped de ...
forged what would eventually become the heavy metal sound through a combined use of high volumes and heavy distortion.


Theory and circuits

The word
distortion In signal processing, distortion is the alteration of the original shape (or other characteristic) of a signal. In communications and electronics it means the alteration of the waveform of an information-bearing signal, such as an audio s ...
refers to any modification of wave form of a
signal In signal processing, a signal is a function that conveys information about a phenomenon. Any quantity that can vary over space or time can be used as a signal to share messages between observers. The '' IEEE Transactions on Signal Processing' ...
, but in music it is used to refer to nonlinear distortion (excluding filters) and particularly to the introduction of new frequencies by memoryless nonlinearities. In music the different forms of linear distortion have specific names describing them. The simplest of these is a distortion process known as "volume adjustment", which involves distorting the amplitude of a sound wave in a proportional (or ‘linear’) way in order to increase or decrease the volume of the sound without affecting the tone quality. In the context of music, the most common source of (nonlinear) distortion is clipping in amplifier circuits and is most commonly known as overdrive. Clipping is a non-linear process that produces
frequencies Frequency is the number of occurrences of a repeating event per unit of time. It is also occasionally referred to as ''temporal frequency'' for clarity, and is distinct from '' angular frequency''. Frequency is measured in hertz (Hz) which is e ...
not originally present in the
audio signal An audio signal is a representation of sound, typically using either a changing level of electrical voltage for analog signals, or a series of binary numbers for digital signals. Audio signals have frequencies in the audio frequency range of ro ...
. These frequencies can be harmonic overtones, meaning they are whole number multiples of one of the signal's original frequencies, or "inharmonic", resulting from general intermodulation distortion. The same nonlinear device will produce both types of distortion, depending on the input signal. Intermodulation occurs whenever the input frequencies are not already harmonically related. For instance, playing a power chord through distortion results in intermodulation that produces new
subharmonic In music, the undertone series or subharmonic series is a sequence of notes that results from inverting the intervals of the overtone series. While overtones naturally occur with the physical production of music on instruments, undertones must ...
s. "Soft clipping" gradually flattens the peaks of a signal which creates a number of higher harmonics which share a harmonic relationship with the original tone. "Hard clipping" flattens peaks abruptly, resulting in higher power in higher harmonics. As clipping increases, a tone input progressively begins to resemble a
square wave A square wave is a non-sinusoidal periodic waveform in which the amplitude alternates at a steady frequency between fixed minimum and maximum values, with the same duration at minimum and maximum. In an ideal square wave, the transitions b ...
which has odd number harmonics. This is generally described as sounding "harsh". Distortion and overdrive circuits each 'clip' the signal before it reaches the main amplifier (clean boost circuits do not necessarily create 'clipping') as well as boost signals to levels that cause distortion to occur at the main amplifier's front end stage (by exceeding the ordinary input signal amplitude, thus ''overdriving'' the amplifier) Note : product names may not accurately reflect type of circuit involved - see above. A fuzz box alters an audio signal until it is nearly a square wave and adds complex overtones by way of a frequency multiplier.


Valve overdrive

Vacuum tube A vacuum tube, electron tube, valve (British usage), or tube (North America), is a device that controls electric current flow in a high vacuum between electrodes to which an electric voltage, potential difference has been applied. The type kn ...
or "valve" distortion is achieved by "overdriving" the valves in an amplifier. In layman's terms, overdriving is pushing the tubes beyond their normal rated maximum. Valve amplifiers—particularly those using class-A triodes—tend to produce asymmetric soft clipping that creates both even and odd harmonics. The increase in even harmonics is considered to create "warm"-sounding overdrive effects. A basic triode valve (tube) contains a
cathode A cathode is the electrode from which a conventional current leaves a polarized electrical device. This definition can be recalled by using the mnemonic ''CCD'' for ''Cathode Current Departs''. A conventional current describes the direction i ...
, a plate and a grid. When a positive
voltage Voltage, also known as electric pressure, electric tension, or (electric) potential difference, is the difference in electric potential between two points. In a static electric field, it corresponds to the work needed per unit of charge t ...
is applied to the plate, a current of negatively charged electrons flows to it from the heated cathode through the grid. This increases the voltage of the
audio signal An audio signal is a representation of sound, typically using either a changing level of electrical voltage for analog signals, or a series of binary numbers for digital signals. Audio signals have frequencies in the audio frequency range of ro ...
, amplifying its volume. The grid regulates the extent to which plate voltage is increased. A small negative voltage applied to the grid causes a large decrease in plate voltage. Valve amplification is more or less linear—meaning the parameters (amplitude, frequency, phase) of the amplified signal are proportional to the input signal—so long as the voltage of the input signal does not exceed the valve's "linear region of operation". The linear region falls between # The saturation region: the voltages at which plate current stops responding to positive increases in grid voltage and # The cutoff region: the voltages at which the charge of the grid is too negative for electrons to flow to the plate. If a valve is biased within the linear region and the input signal's voltage exceeds this region, overdrive and non-linear clipping will occur. Multiple stages of valve gain/clipping can be "cascaded" to produce a thicker and more complex distortion sound. In layperson's terms, a musician will plug a fuzz pedal into a tube amp that is being "cranked" to a clipping "overdriven" condition; as such, the musician will get the distortion from the fuzz which is then distorted further by the amp. During the 1990s, some Seattle grunge guitarists chained together as many as four fuzz pedals to create a thick "
wall of sound The Wall of Sound (also called the Spector Sound) is a music production formula developed by American record producer Phil Spector at Gold Star Studios, in the 1960s, with assistance from engineer Larry Levine and the conglomerate of sessio ...
" of distortion. In some modern valve effects, the "dirty" or "gritty" tone is actually achieved not by high voltage, but by running the circuit at voltages that are too low for the circuit components, resulting in greater non-linearity and distortion. These designs are referred to as "starved plate" configurations, and result in an "amp death" sound.


Solid-state distortion

Solid-state Solid state, or solid matter, is one of the four fundamental states of matter. Solid state may also refer to: Electronics * Solid-state electronics, circuits built of solid materials * Solid state ionics, study of ionic conductors and their ...
amplifiers incorporating
transistor upright=1.4, gate (G), body (B), source (S) and drain (D) terminals. The gate is separated from the body by an insulating layer (pink). A transistor is a semiconductor device used to Electronic amplifier, amplify or electronic switch, switch ...
s and/or
op amp An operational amplifier (often op amp or opamp) is a DC-coupled high-gain electronic voltage amplifier with a differential input and, usually, a single-ended output. In this configuration, an op amp produces an output potential (relative to ...
s can be made to produce hard clipping. When symmetrical, this adds additional high-amplitude odd harmonics, creating a "dirty" or "gritty" tone. When asymmetrical, it produces both even and odd harmonics. Electronically, this is usually achieved by either amplifying the signal to a point where it is clipped by the
DC voltage Direct current (DC) is one-directional electric current, flow of electric charge. An electrochemical cell is a prime example of DC power. Direct current may flow through a conductor (material), conductor such as a wire, but can also flow throug ...
limitation of the power supply rail, or by clipping the signal with diodes. Many solid-state distortion devices attempt to emulate the sound of overdriven vacuum valves using additional solid-state circuitry. Some amplifiers (notably the Marshall JCM 900) utilize hybrid designs that employ both valve and solid-state components.


Approaches

Guitar distortion can be produced by many components of the guitar's signal path, including effects pedals, the pre-amplifier, power amplifier, and speakers. Many players use a combination of these to obtain their "signature" tone.


Pre-amplifier distortion

The
pre-amplifier A preamplifier, also known as a preamp, is an electronic amplifier that converts a weak electrical signal into an output signal strong enough to be noise-tolerant and strong enough for further processing, or for sending to a power amplifier ...
section of a guitar amplifier serves to amplify a weak instrument signal to a level that can drive the power amplifier. It often also contains circuitry to shape the tone of the instrument, including equalization and
gain Gain or GAIN may refer to: Science and technology * Gain (electronics), an electronics and signal processing term * Antenna gain * Gain (laser), the amplification involved in laser emission * Gain (projection screens) * Information gain in d ...
controls. Often multiple cascading gain/clipping stages are employed to generate distortion. Because the first component in a valve amplifier is a valve gain stage, the output level of the preceding elements of the signal chain has a strong influence on the distortion created by that stage. The output level of the guitar's pickups, the setting of the guitar's volume knob, how hard the strings are plucked, and the use of volume-boosting effects pedals can drive this stage harder and create more distortion. During the 1980s and 1990s, most valve amps featured a "master volume" control, an adjustable attenuator between the preamp section and the power amp. When the preamp volume is set high to generate high distortion levels, the master volume lowered, keeping the output volume at manageable levels.


Overdrive/distortion pedals

Analog overdrive/distortion pedals work on similar principles to preamplifier distortion. Because most effects pedals are designed to operate from battery voltages, using vacuum tubes to generate distortion and overdrive is impractical; instead, most pedals use solid-state transistors,
op-amp An operational amplifier (often op amp or opamp) is a DC-coupled high- gain electronic voltage amplifier with a differential input and, usually, a single-ended output. In this configuration, an op amp produces an output potential (relative t ...
s and diodes. Classic examples of overdrive/distortion pedals include the Boss OD series (overdrives), the Ibanez Tube Screamer (an overdrive), the Electro-Harmonix Big Muff Pi (a fuzz box) and the
Pro Co RAT The Pro Co "The RAT" is a distortion pedal produced by Pro Co Sound. The original RAT was developed in the basement of Pro Co's Kalamazoo, Michigan facility in 1978. Numerous variations of the original RAT pedal are still being produced today. The ...
(a distortion). Typically, "overdrive" pedals are designed to produce sounds associated with classic rock or blues, with "distortion" pedals producing the "high gain, scooped mids" sounds associated with heavy metal; fuzz boxes are designed to emulate the distinctive sound of the earliest overdrive pedals such as the Big Muff and the Fuzz Face. Most overdrive/distortion pedals can be used in two ways: a pedal can be used as a "boost" with an already overdriven amplifier to drive it further into saturation and "color" the tone, or it can be used with a completely clean amplifier to generate the whole overdrive/distortion effect. With care—and with appropriately chosen pedals—it is possible to "stack" multiple overdrive/distortion pedals together, allowing one pedal to act as a 'boost' for another. Fuzz boxes and other heavy distortions can produce unwanted dissonances when playing chords. To get around this, guitar players (and keyboard players) using these effects may restrict their playing to single notes and simple " power chords" (root, fifth, and octave). Indeed, with the most extreme fuzz pedals, players may choose to play mostly single notes, because the fuzz can make even single notes sound very thick and heavy. Heavy distortion also tends to limit the player's control of dynamics (loudness and softness)—similar to the limitations imposed on a
Hammond organ The Hammond organ is an electric organ invented by Laurens Hammond and John M. Hanert and first manufactured in 1935. Multiple models have been produced, most of which use sliding #Drawbars, drawbars to vary sounds. Until 1975, Hammond organs ...
player (Hammond organ does not produce louder or softer sounds depending on how hard or soft the performer plays the keys; however, the performer can still control the volume with drawbars and the expression pedal). Heavy metal music has evolved around these restrictions, using complex rhythms and timing for expression and excitement. Lighter distortions and overdrives can be used with triadic chords and seventh chords; as well, lighter overdrive allows more control of dynamics.


Power amplifier distortion

Power valves (tubes) can be overdriven in the same way that pre-amplifier valves can, but because these valves are designed to output more power, the distortion and character they add to the guitar's tone is unique. During the 1960s to early 1970s, distortion was primarily created by overdriving the power valves. Because they have become accustomed to this sound , many guitar players favour this type of distortion, and thus set their amps to maximum levels in order to drive the power section hard. Many valve-based amplifiers in common use have a push-pull output configuration in their power section, with matched pairs of tubes driving the output transformer. Power amplifier distortion is normally entirely symmetric, generating predominantly odd-order harmonics. Because driving the power valves this hard also means maximum volume, which can be difficult to manage in a small recording or rehearsal space, many solutions have emerged that in some way divert some of this power valve output from the speakers, and allow the player to generate power valve distortion without excessive volume. These include built-in or separate power attenuators and power-supply-based power attenuation, such as a VVR, or Variable Voltage Regulator to drop the voltage on the valves' plates, to increase distortion whilst lowering volume. Guitarists such as Eddie Van Halen have been known to use variacs before VVR technology was invented. Lower-power valve amps (such as a quarter-watt or less), speaker isolation cabinets, and low-efficiency guitar speakers are also used to tame the volume. Power-valve distortion can also be produced in a dedicated rackmount valve power amp. A modular rackmount setup often involves a
rackmount A 19-inch rack is a standardized frame or enclosure for mounting multiple electronic equipment modules. Each module has a front panel that is wide. The 19 inch dimension includes the edges or "ears" that protrude from each side of the equ ...
preamp, a rackmount valve power amp, and a rackmount dummy load to attenuate the output to desired volume levels. Some effects pedals internally produce power-valve distortion, including an optional dummy load for use as a power-valve distortion pedal. Such effects units can use a preamp valve such as the
12AX7 12AX7 (also known as ECC83) is a miniature dual-triode 6AV6 vacuum tube with high voltage gain. Developed around 1946 by RCA engineers in Camden, New Jersey, under developmental number A-4522, it was released for public sale under the 12AX7 ident ...
in a power-valve circuit configuration (as in the Stephenson's Stage Hog), or use a conventional power valve, such as the EL84 (as in the H&K Crunch Master compact tabletop unit). However, because these are usually placed before the pre-amplifier in the signal chain, they contribute to the overall tone in a different way. Power amplifier distortion may damage speakers. A Direct Inject signal can capture the power-tube distortion sound without the direct coloration of a guitar speaker and microphone. This DI signal can be blended with a miked guitar speaker, with the DI providing a more present, immediate, bright sound, and the miked guitar speaker providing a colored, remote, darker sound. The DI signal can be obtained from a DI jack on the guitar amp, or from the Line Out jack of a power attenuator.


Output transformer distortion

The output
transformer A transformer is a passive component that transfers electrical energy from one electrical circuit to another circuit, or multiple circuits. A varying current in any coil of the transformer produces a varying magnetic flux in the transformer' ...
sits between the power valves and the speaker, serving to match impedance. When a transformer's ferromagnetic core becomes electromagnetically saturated a loss of inductance takes place, since the back E.M.F. is reliant on a change in flux in the core. As the core reaches saturation, the flux levels off and cannot increase any further. With no change in flux there is no back E.M.F. and hence no reflected impedance. The transformer and valve combination then generate large 3rd order harmonics. So long as the core does not go into saturation, the valves will clip naturally as they drop the available voltage across them. In single ended systems the output harmonics will be largely even ordered due to the valve's relatively non linear characteristics at large signal swings. This is only true however if the magnetic core does NOT saturate.


Power supply "sag"

Early valve amplifiers used unregulated power supplies. This was due to the high cost associated with high-quality high-voltage power supplies. The typical
anode An anode is an electrode of a polarized electrical device through which conventional current enters the device. This contrasts with a cathode, an electrode of the device through which conventional current leaves the device. A common mnemoni ...
(plate) supply was simply a rectifier, an inductor and a
capacitor A capacitor is a device that stores electrical energy in an electric field by virtue of accumulating electric charges on two close surfaces insulated from each other. It is a passive electronic component with two terminals. The effect of a ...
. When the valve amplifier was operated at high
volume Volume is a measure of occupied three-dimensional space. It is often quantified numerically using SI derived units (such as the cubic metre and litre) or by various imperial or US customary units (such as the gallon, quart, cubic inch). Th ...
, the
power supply A power supply is an electrical device that supplies electric power to an electrical load. The main purpose of a power supply is to convert electric current from a source to the correct voltage, current, and frequency to power the load. As a ...
voltage Voltage, also known as electric pressure, electric tension, or (electric) potential difference, is the difference in electric potential between two points. In a static electric field, it corresponds to the work needed per unit of charge t ...
would dip, reducing power output and causing signal attenuation and compression. This dipping effect is known as "sag", and is sought-after by some electric guitarists. Sag only occurs in class-AB amplifiers. This is because, technically, sag results from more current being drawn from the power supply, causing a greater voltage drop over the rectifier valve. Class AB amplifiers draw the most power at both the maximum and minimum point of the signal, putting more stress on the power supply than class A, which only draws maximum power at the peak of the signal. As this effect is more pronounced with higher input signals, the harder "attack" of a note will be compressed more heavily than the lower-voltage "decay", making the latter seem louder and thereby improving sustain. Additionally, because the level of compression is affected by input volume, the player can control it via their playing intensity: playing harder results in more compression or "sag". In contrast, modern amplifiers often use high-quality, well-regulated power supplies.


Speaker distortion

Guitar
loudspeakers A loudspeaker (commonly referred to as a speaker or speaker driver) is an electroacoustic transducer that converts an electrical audio signal into a corresponding sound. A ''speaker system'', also often simply referred to as a "speaker" or "l ...
are designed differently from high fidelity stereo speakers or public address system speakers. While hi-fi and public address speakers are designed to reproduce the sound with as little distortion as possible, guitar speakers are usually designed so that they will shape or color the tone of the guitar, either by enhancing some frequencies or attenuating unwanted frequencies. When the power delivered to a guitar speaker approaches its maximum rated power, the speaker's performance degrades, causing the speaker to "break up", adding further distortion and colouration to the signal. Some speakers are designed to have much clean headroom, while others are designed to break up early to deliver grit and growl.


Amp modeling for distortion emulation

Guitar amp modeling devices and software can reproduce various guitar-specific distortion qualities that are associated with a range of popular "stomp box" pedals and amplifiers. Amp modeling devices typically use
digital signal processing Digital signal processing (DSP) is the use of digital processing, such as by computers or more specialized digital signal processors, to perform a wide variety of signal processing operations. The digital signals processed in this manner ar ...
to recreate the sound of plugging into analogue pedals and overdriven valve amplifiers. The most sophisticated devices allow the user to customize the simulated results of using different preamp, power-tube, speaker distortion, speaker cabinet, and microphone placement combinations. For example, a guitarist using a small amp modeling pedal could simulate the sound of plugging their electric guitar into a heavy vintage valve amplifier and a stack of 8 X 10" speaker cabinets.


Voicing with equalization

Guitar distortion is obtained and shaped at various points in the signal processing chain, including multiple stages of preamp distortion, power valve distortion, output and power transformer distortion, and guitar speaker distortion. Much of the distortion character or voicing is controlled by the frequency response before and after each distortion stage. This dependency of distortion voicing on frequency response can be heard in the effect that a wah pedal has on the subsequent distortion stage, or by using tone controls built into the guitar, the preamp or an EQ pedal to favor the bass or treble components of the guitar pickup signal prior to the first distortion stage. Some guitarists place an equalizer pedal after the distortion effect, to emphasize or de-emphasize different frequencies in the distorted signal. Increasing the bass and treble while reducing or eliminating the centre midrange (750 Hz) results in what is popularly known as a "scooped" sound (since the midrange frequencies are "scooped" out). Conversely, decreasing the bass while increasing the midrange and treble creates a punchy, harsher sound. Rolling off all of the treble produces a dark, heavy sound.


Avoiding distortion

While musicians intentionally create or add distortion to electric instrument signals or vocals to create a musical effect, there are some musical styles and musical applications where as little distortion as possible is sought. When DJs are playing recorded music in a
nightclub A nightclub (music club, discothèque, disco club, or simply club) is an entertainment venue during nighttime comprising a dance floor, lightshow, and a stage for live music or a disc jockey (DJ) who plays recorded music. Nightclubs gener ...
, they typically seek to reproduce the recordings with little or no distortion. In many musical styles, including
pop music Pop music is a genre of popular music that originated in its modern form during the mid-1950s in the United States and the United Kingdom. The terms ''popular music'' and ''pop music'' are often used interchangeably, although the former describ ...
,
country music Country (also called country and western) is a genre of popular music that originated in the Southern and Southwestern United States in the early 1920s. It primarily derives from blues, church music such as Southern gospel and spirituals, o ...
and even genres where the electric guitars are almost always distorted, such as heavy metal, punk and hard rock, sound engineers usually take a number of steps to ensure that the vocals sounding through the sound reinforcement system are undistorted (the exception is the rare cases where distortion is purposely added to vocals in a song as a special effect). Sound engineers prevent unwanted, unintended distortion and clipping using a number of methods. They may reduce the gain on microphone preamplifiers on the
audio console A mixing console or mixing desk is an electronic device for Audio mixing (recorded music), mixing audio signals, used in sound recording and reproduction and sound reinforcement systems. Inputs to the console include microphones, signals fro ...
; use attenuation "pads" (a button on audio console channel strips, DI unit and some bass amplifiers); and use electronic audio compressor effects and limiters to prevent sudden volume peaks from vocal mics from causing unwanted distortion. Though some
bass guitar The bass guitar, electric bass or simply bass (), is the lowest-pitched member of the string family. It is a plucked string instrument similar in appearance and construction to an electric or an acoustic guitar, but with a longer neck and s ...
players in metal and punk bands intentionally use fuzz bass to distort their bass sound, in other genres of music, such as pop,
big band A big band or jazz orchestra is a type of musical ensemble of jazz music that usually consists of ten or more musicians with four sections: saxophones, trumpets, trombones, and a rhythm section. Big bands originated during the early 1910s ...
jazz and traditional
country music Country (also called country and western) is a genre of popular music that originated in the Southern and Southwestern United States in the early 1920s. It primarily derives from blues, church music such as Southern gospel and spirituals, o ...
, bass players typically seek an undistorted bass sound. To obtain a clear, undistorted bass sound, professional bass players in these genres use high-powered amplifiers with a lot of " headroom" and they may also use audio compressors to prevent sudden volume peaks from causing distortion. In many cases, musicians playing stage pianos or
synthesizer A synthesizer (also spelled synthesiser) is an electronic musical instrument that generates audio signals. Synthesizers typically create sounds by generating waveforms through methods including subtractive synthesis, additive synthesis ...
s use
keyboard amplifier A keyboard amplifier is a powered instrument amplifier, electronic amplifier and loudspeaker in a wooden speaker enclosure, speaker cabinet used for amplification of electronic keyboard instruments. Keyboard amplifiers are distinct from other ...
s that are designed to reproduce the audio signal with as little distortion as possible. The exceptions with keyboards are the
Hammond organ The Hammond organ is an electric organ invented by Laurens Hammond and John M. Hanert and first manufactured in 1935. Multiple models have been produced, most of which use sliding #Drawbars, drawbars to vary sounds. Until 1975, Hammond organs ...
as used in blues and the Fender Rhodes as used in rock music; with these instruments and genres, keyboardists often purposely overdrive a tube amplifier to get a natural overdrive sound. Another example of instrument amplification where as little distortion as possible is sought is with acoustic instrument amplifiers, designed for musicians playing instruments such as the
mandolin A mandolin ( it, mandolino ; literally "small mandola") is a stringed musical instrument in the lute family and is generally plucked with a pick. It most commonly has four courses of doubled strings tuned in unison, thus giving a total of 8 ...
or fiddle in a folk or bluegrass style.


See also

*
Distortion meter A distortion meter is a type of electronic test equipment used to determine specific frequencies that cause distortion in electronic devices. The device is primarily used in audio related equipment. Features and uses A typical unit injects a sig ...
*
Guitar pedalboard A guitar pedalboard is a flat board or panel that serves as a container, patch bay, and power supply for effects pedals for the electric guitar. Some pedalboards contain their own transformer and power cables to power multiple pedals. Pedalboard ...
* Tube sound/Valve sound


References


External links


A Musical Distortion Primer
(R.G. Keen) Article on the physics of distortion and electronic techniques

(Jon Blackstone) Article on the physics of distortion, with interactive demonstrations
Amptone.com
An archived version of a website on overdriven guitar amplifier and effects, covering: tone settings, distortion voicing, simulation and modeling, processors, speakers, power-supply modifications, switching and signal routing gear, software and recording, and DIY projects.
AX84
Cooperative, non-profit website offering free schematics and plans for building guitar amps.
Fuzz Central
Many schematics and DIY fuzz pedal projects

Technical website with information on multiFX pedals {{DEFAULTSORT:Distortion (Music) Amplified instruments Effects units Electric guitars Audio effects