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Distortion (guitar)
Encyclopedia
Distortion effects create "warm", "dirty" and "fuzzy" sounds by compressing the peaks of a musical instrument
's sound wave and adding overtone
s. The three principal types of distortion effects are overdrive, distortion and fuzz. Distortion effects are sometimes called “gain
” effects, as distorted guitar sounds were first achieved by over-driving tube amplifiers. Distortion has long been integral to the sound of rock and roll
music, and is important to other music genres such as electric blues
and jazz
.
The terms “distortion”, “overdrive” and “fuzz” are often used interchangeably, but they have subtle differences in meaning. Overdrive effects are the mildest of the three, producing "warm" overtones at quieter volumes and harsher distortion as gain
is increased. A "distortion" effect produces approximately the same amount of distortion at any volume, and its sound alterations are much more pronounced and intense. A fuzzbox (or “fuzz box”) alters an audio signal until it is nearly a square wave
and adds complex overtones by way of a frequency multiplier
.
Distortion can be produced by effects pedals and rackmounts, pre-amplifiers, power amplifiers, speaker
s and more recently, digital amplifier modeling
devices and software.
The first amplifier
s built for electric guitar were relatively low-fidelity
, and would often produce distortion when their volume (gain
) was increased beyond their design limit or if they sustained minor damage. One of the earliest recorded examples of distortion in rock music is the 1951 Ike Turner and the Kings of Rhythm
song "Rocket 88
", on which guitarist Willie Kizart used an amplifier that had been slightly damaged in transport. In the early 1950s, pioneering rock guitarist Willie Johnson
of Howlin' Wolf
began deliberately increasing gain beyond its intended levels to produce "warm" distorted sounds. Chuck Berry
's 1955 classic "Maybellene
" features a guitar solo with warm overtone
s created by his small valve amplifier
.
By the mid 1950s rock guitarists began intentionally "doctoring" amplifiers and speakers in order to create even harsher distortion. In 1956 guitarist Paul Burlison of the Johnny Burnette Trio deliberately dislodged a vacuum tube
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. 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. The resultant sound can be heard on his highly influential 1958 instrumental
, "Rumble".
In 1961, the American instrumental rock band The Ventures
asked their friend session musician and electronics enthusiast Orville "Red" Rhodes for help recreating the “fuzz” sound caused by a faulty preamplifier
on Grady Martin
’s guitar track for the Marty Robbins
song "Don't Worry
". Rhodes offered The Ventures a fuzzbox he had made, which they used to record "2000 Pound Bee" in 1962. The first purpose-designed commercial distortion circuit was the Maestro "Fuzz Tone" Model FZ-1, released in 1962.
Distortion gained widespread popularity after guitarist Dave Davies
of The Kinks
used a razor blade to slash his speaker cones for the 1964 single "You Really Got Me
". The song was a number one hit and the first rock and roll track to feature a distorted power chord
riff. In 1966, Jim Marshall of the British company Marshall Amplification
began modifying the electronic circuitry of his amplifiers so as to achieve a "brighter, louder" sound and fuller distortion capabilities.
In May 1965 Keith Richards
used a Gibson
Maestro 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. Early fuzzboxes include the Mosrite FuzzRITE and Arbiter Group Fuzz Face
used by Jimi Hendrix
, the Electro-Harmonix
Big Muff Pi used by Hendrix and Carlos Santana
, and the Vox
Tone Bender used by Paul McCartney
on "Think for Yourself
" and other Beatles recordings.
In the late 1960s and early 1970s hard rock
bands such as Deep Purple
, Led Zeppelin
and Black Sabbath
forged what would eventually become the heavy metal
sound through a combined use of high volumes and heavy distortion.
.
Clipping is a non-linear process that produces frequencies
not originally present in the audio signal
. These frequencies can either be "harmonic
", meaning they are whole number multiples of the signal's original frequencies, or "inharmonic", meaning dissonant
odd-order overtones. Harmonic distortion produces harmonically related overtones while intermodulation distortion produces inharmonic overtones.
"Soft clipping" gradually flattens the peaks of a signal and de-emphasizes higher odd harmonics. "Hard clipping" flattens peaks abruptly, resulting in harsh-sounding, high amplitude
odd harmonics.
Distortion circuits distort a signal before it reaches the main amplifier. Overdrive circuits do not create distortion themselves but rather boost signals to levels that cause distortion to occur at the main amplifier's front end stage.
or “valve” distortion is achieved by “overdriving” the valves in an amplifier.Valve amplifiers--particularly those using triode
s--tend to produce asymmetric soft clipping that creates "warm"-sounding even-order harmonics.
A basic triode valve contains a cathode, a plate and a grid. When a positive voltage
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, 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 1. the saturation region: the voltages at which plate current stops responding to positive increases in grid voltage and 2. 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 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.
s and/or op amps and are prone to produce hard clipping and symmetrical distortion when overdriven. This adds additional high-amplitude odd harmonics, creating a "dirty" or "gritty" tone. Electronically, this is usually achieved by either amplifying the signal to a point where it must be clipped to the supply rails, or by clipping the signal across 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.
and the Electro-Harmonix Big Muff
.
To reduce unwanted dissonance, single notes and simple power chord
s (root, fifth, and octave) are often used when using fuzzboxes, rather than triads (root, third, and fifth) or four-note chords (root, third, fifth, and seventh).
and gain
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, many amps featured a "master volume" control, an adjustable attenuator between the preamp section and the power amp. When the preamp is set up to generate high distortion levels the master volume can be used to divert most of the resulting signal away from the power valves, keeping the output volume at manageable levels.
Power valves 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 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, 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. 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
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
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.
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.
sits between the power valves and the speaker, serving to match impedance
. When a transformer's ferromagnetic core becomes electromagnetically saturated, it will clip symmetrically. This adds additional odd-order distortion to the signal delivered to the speakers.
supply was simply a rectifier
, an inductor and a capacitor
. When the valve amplifier was operated at high volume
, the power supply
voltage
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. In a Class A amplifier, current draw is constant, so sag does not occur.
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.
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 lots of clean headroom, while others are designed to break up early to deliver grit and growl.
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.
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 in to 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.
Musical instrument
A musical instrument is a device created or adapted for the purpose of making musical sounds. In principle, any object that produces sound can serve as a musical instrument—it is through purpose that the object becomes a musical instrument. The history of musical instruments dates back to the...
's sound wave and adding overtone
Overtone
An overtone is any frequency higher than the fundamental frequency of a sound. The fundamental and the overtones together are called partials. Harmonics are partials whose frequencies are whole number multiples of the fundamental These overlapping terms are variously used when discussing the...
s. The three principal types of distortion effects are overdrive, distortion and fuzz. Distortion effects are sometimes called “gain
Gain
In electronics, gain is a measure of the ability of a circuit to increase the power or amplitude of a signal from the input to the output. It is usually defined as the mean ratio of the signal output of a system to the signal input of the same system. It may also be defined on a logarithmic scale,...
” effects, as distorted guitar sounds were first achieved by over-driving tube amplifiers. Distortion has long been integral to the sound of rock and roll
Rock and roll
Rock and roll is a genre of popular music that originated and evolved in the United States during the late 1940s and early 1950s, primarily from a combination of African American blues, country, jazz, and gospel music...
music, and is important to other music genres such as electric blues
Electric blues
Electric blues is a type of blues music distinguished by the amplification of the guitar, bass guitar, drums, and often the harmonica. Pioneered in the 1930s, it emerged as a genre in Chicago in the 1940s. It was taken up in many areas of America leading to the development of regional subgenres...
and jazz
Jazz
Jazz is a musical style that originated at the beginning of the 20th century in African American communities in the Southern United States. It was born out of a mix of African and European music traditions. From its early development until the present, jazz has incorporated music from 19th and 20th...
.
The terms “distortion”, “overdrive” and “fuzz” are often used interchangeably, but they have subtle differences in meaning. Overdrive effects are the mildest of the three, producing "warm" overtones at quieter volumes and harsher distortion as gain
Gain
In electronics, gain is a measure of the ability of a circuit to increase the power or amplitude of a signal from the input to the output. It is usually defined as the mean ratio of the signal output of a system to the signal input of the same system. It may also be defined on a logarithmic scale,...
is increased. A "distortion" effect produces approximately the same amount of distortion at any volume, and its sound alterations are much more pronounced and intense. A fuzzbox (or “fuzz box”) alters an audio signal until it is nearly a square wave
Square wave
A square wave is a kind of non-sinusoidal waveform, most typically encountered in electronics and signal processing. An ideal square wave alternates regularly and instantaneously between two levels...
and adds complex overtones by way of a frequency multiplier
Frequency multiplier
In electronics, a frequency multiplier is an electronic circuit that generates an output signal whose output frequency is a harmonic of its input frequency. Frequency multipliers consist of a nonlinear circuit that distorts the input signal and consequently generates harmonics of the input signal...
.
Distortion can be produced by effects pedals and rackmounts, pre-amplifiers, power amplifiers, speaker
Loudspeaker
A loudspeaker is an electroacoustic transducer that produces sound in response to an electrical audio signal input. Non-electrical loudspeakers were developed as accessories to telephone systems, but electronic amplification by vacuum tube made loudspeakers more generally useful...
s and more recently, digital amplifier modeling
Amplifier modeling
Amplifier modeling is the process of digitally emulating a physical amplifier such as a guitar amplifier. Amp modeling may appear as software, such as plugins for DAWs which may be aided by computer hardware accelerators, or may be part of a standalone device or amplifier...
devices and software.
History
Guitar amplifier
A guitar amplifier is an electronic amplifier designed to make the signal of an electric or acoustic guitar louder so that it will produce sound through a loudspeaker...
s built for electric guitar were relatively low-fidelity
High fidelity
High fidelity—or hi-fi—reproduction is a term used by home stereo listeners and home audio enthusiasts to refer to high-quality reproduction of sound or images, to distinguish it from the poorer quality sound produced by inexpensive audio equipment...
, and would often produce distortion when their volume (gain
Gain
In electronics, gain is a measure of the ability of a circuit to increase the power or amplitude of a signal from the input to the output. It is usually defined as the mean ratio of the signal output of a system to the signal input of the same system. It may also be defined on a logarithmic scale,...
) was increased beyond their design limit or if they sustained minor damage. One of the earliest recorded examples of distortion in rock music is the 1951 Ike Turner and the Kings of Rhythm
Ike Turner
Isaac Wister Turner was an American musician, bandleader, songwriter, arranger, talent scout, and record producer. In a career that lasted more than half a century, his repertoire included blues, soul, rock, and funk...
song "Rocket 88
Rocket 88
"Rocket 88" is a rhythm and blues song that was first recorded at Sam Phillips' recording studio in Memphis, Tennessee, on 3 March or 5 March 1951...
", on which guitarist Willie Kizart used an amplifier that had been slightly damaged in transport. In the early 1950s, pioneering rock guitarist Willie Johnson
Willie Johnson
Willie Johnson was an American blues guitarist. He is best known as the principal guitarist in Howlin' Wolf's band from 1948 to 1953. His raucous, distorted guitar playing features on Howlin' Wolf's Memphis recordings of 1951-3, including the 1951 hit "How Many More Years"...
of Howlin' Wolf
Howlin' Wolf
Chester Arthur Burnett , known as Howlin' Wolf, was an influential American blues singer, guitarist and harmonica player....
began deliberately increasing gain beyond its intended levels to produce "warm" distorted sounds. Chuck Berry
Chuck Berry
Charles Edward Anderson "Chuck" Berry is an American guitarist, singer, and songwriter, and one of the pioneers of rock and roll music. With songs such as "Maybellene" , "Roll Over Beethoven" , "Rock and Roll Music" and "Johnny B...
's 1955 classic "Maybellene
Maybellene
"Maybellene" is a song recorded by Chuck Berry, adapted from the traditional fiddle tune "Ida Red" that tells the story of a hot rod race and a broken romance. It was released in July 1955 as a single on Chess Records of Chicago, Illinois. It was Berry's first single release and his first hit...
" features a guitar solo with warm overtone
Overtone
An overtone is any frequency higher than the fundamental frequency of a sound. The fundamental and the overtones together are called partials. Harmonics are partials whose frequencies are whole number multiples of the fundamental These overlapping terms are variously used when discussing the...
s created by his small valve amplifier
Valve amplifier
A valve amplifier or tube amplifier is a type of electronic amplifier that makes use of vacuum tubes to increase the power and/or amplitude of a signal. Low to medium power valve amplifiers for frequencies below the microwaves were largely replaced by solid state amplifiers during the 1960s and...
.
By the mid 1950s rock guitarists began intentionally "doctoring" amplifiers and speakers in order to create even harsher distortion. In 1956 guitarist Paul Burlison of the Johnny Burnette Trio deliberately dislodged a vacuum tube
Vacuum tube
In electronics, a vacuum tube, electron tube , or thermionic valve , reduced to simply "tube" or "valve" in everyday parlance, is a device that relies on the flow of electric current through a vacuum...
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. Guitarist Link Wray
Link Wray
Fred Lincoln "Link" Wray Jr was an American rock and roll guitarist, songwriter and occasional singer....
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. The resultant sound can be heard on his highly influential 1958 instrumental
Instrumental
An instrumental is a musical composition or recording without lyrics or singing, although it might include some non-articulate vocal input; the music is primarily or exclusively produced by musical instruments....
, "Rumble".
In 1961, the American instrumental rock band The Ventures
The Ventures
The Ventures is an American instrumental rock band formed in 1958 in Tacoma, Washington. Founded by Don Wilson and Bob Bogle, the group in its various incarnations has had an enduring impact on the development of music worldwide. With over 100 million records sold, the group is the best-selling...
asked their friend session musician and electronics enthusiast Orville "Red" Rhodes for help recreating the “fuzz” sound caused by a faulty preamplifier
Preamplifier
A preamplifier is an electronic amplifier that prepares a small electrical signal for further amplification or processing. A preamplifier is often placed close to the sensor to reduce the effects of noise and interference. It is used to boost the signal strength to drive the cable to the main...
on Grady Martin
Grady Martin
Thomas Grady Martin was one of the most renowned, inventive and historically significant American session musicians in country music and rockabilly....
’s guitar track for the Marty Robbins
Marty Robbins
Martin David Robinson , known professionally as Marty Robbins, was an American singer, songwriter, and multi-instrumentalist...
song "Don't Worry
Don't Worry (Marty Robbins song)
"Don't Worry" is a 1961 country/pop single written and recorded by Marty Robbins. "Don't Worry" was Marty Robbins seventh number one on the country chart and stayed at number one for ten weeks...
". Rhodes offered The Ventures a fuzzbox he had made, which they used to record "2000 Pound Bee" in 1962. The first purpose-designed commercial distortion circuit was the Maestro "Fuzz Tone" Model FZ-1, released in 1962.
Dave Davies
David Russell Gordon "Dave" Davies is an English rock musician best known for his role as lead guitarist and vocalist for the English rock band The Kinks....
of The Kinks
The Kinks
The Kinks were an English rock band formed in Muswell Hill, North London, by brothers Ray and Dave Davies in 1964. Categorised in the United States as a British Invasion band, The Kinks are recognised as one of the most important and influential rock acts of the era. Their music was influenced by a...
used a razor blade to slash his speaker cones for the 1964 single "You Really Got Me
You Really Got Me
"You Really Got Me" is a rock song written by Ray Davies and performed by his band, The Kinks. It was released on 4th August 1964 as the group's third single, and reached Number 1 on the UK singles chart the next month, remaining for two weeks...
". The song was a number one hit and the first rock and roll track to feature a distorted power chord
Power chord
In music, a power chord is a chord consisting of only the root note of the chord and the fifth interval, usually played on electric guitar, and typically through an amplification process that imparts distortion...
riff. In 1966, Jim Marshall of the British company Marshall Amplification
Marshall Amplification
Marshall Amplification is a British company, founded by drummer Jim Marshall, that designs and manufactures music amplifiers, brands personal headphones/earphones , and, after acquiring Natal Drums, drums and bongos. Marshall amplifiers, and specifically their guitar amplifiers, are among the most...
began modifying the electronic circuitry of his amplifiers so as to achieve a "brighter, louder" sound and fuller distortion capabilities.
In May 1965 Keith Richards
Keith Richards
Keith Richards is an English musician, songwriter, and founding member of the Rolling Stones. Rolling Stone magazine said Richards had created "rock's greatest single body of riffs", and placed him as the "10th greatest guitarist of all time." Fourteen songs written by Richards and songwriting...
used a Gibson
Gibson Guitar Corporation
The Gibson Guitar Corporation, formerly of Kalamazoo, Michigan and currently of Nashville, Tennessee, manufactures guitars and other instruments which sell under a variety of brand names...
Maestro Fuzz-Tone to record "(I Can't Get No) Satisfaction
(I Can't Get No) Satisfaction
" Satisfaction" is a song by the English rock band The Rolling Stones, released in 1965. It was written by Mick Jagger and Keith Richards and produced by Andrew Loog Oldham. Richards's throwaway three-note guitar riff — intended to be replaced by horns — opens and drives the song...
". The song's success greatly boosted sales of the device, and all available stock sold out by the end of 1965. Early fuzzboxes include the Mosrite FuzzRITE and Arbiter Group Fuzz Face
Fuzz Face
The Fuzz Face is an effects pedal used mainly by electric guitarists, and by some bass players. It is a stompbox designed to produce a distorted sound from an electric guitar. This "fuzz" sound is sometimes compared to the sound of a damaged speaker...
used by Jimi Hendrix
Jimi Hendrix
James Marshall "Jimi" Hendrix was an American guitarist and singer-songwriter...
, the Electro-Harmonix
Electro-Harmonix
Electro-Harmonix is a New York-based company that makes high-end electronic audio processors. The company was founded by Mike Matthews in 1968. They are most famous for a series of popular guitar effects pedals introduced in the 1970s and 1990s....
Big Muff Pi used by Hendrix and Carlos Santana
Carlos Santana
Carlos Augusto Alves Santana is a Mexican rock guitarist. Santana became famous in the late 1960s and early 1970s with his band, Santana, which pioneered rock, salsa and jazz fusion...
, and the Vox
Vox (musical equipment)
Vox is a musical equipment manufacturer which is most famous for making the Vox AC30 guitar amplifier, the Vox Continental electric organ, and a series of innovative but commercially unsuccessful electric guitars and bass guitars...
Tone Bender used by Paul McCartney
Paul McCartney
Sir James Paul McCartney, MBE, Hon RAM, FRCM is an English musician, singer-songwriter and composer. Formerly of The Beatles and Wings , McCartney is listed in Guinness World Records as the "most successful musician and composer in popular music history", with 60 gold discs and sales of 100...
on "Think for Yourself
Think For Yourself
"Think for Yourself" is a song by British rock band The Beatles which first appeared on their 1965 album Rubber Soul. Written and sung by George Harrison, it is a warning against listening to lies. In his book I Me Mine he writes, "But all this time later, I don't quite recall who inspired that tune...
" and other Beatles recordings.
In the late 1960s and early 1970s hard rock
Hard rock
Hard rock is a loosely defined genre of rock music which has its earliest roots in mid-1960s garage rock, blues rock and psychedelic rock...
bands such as Deep Purple
Deep Purple
Deep Purple are an English rock band formed in Hertford in 1968. Along with Led Zeppelin and Black Sabbath, they are considered to be among the pioneers of heavy metal and modern hard rock, although some band members believe that their music cannot be categorised as belonging to any one genre...
, Led Zeppelin
Led Zeppelin
Led Zeppelin were an English rock band, active in the late 1960s and throughout the 1970s. Formed in 1968, they consisted of guitarist Jimmy Page, singer Robert Plant, bassist/keyboardist John Paul Jones, and drummer John Bonham...
and Black Sabbath
Black Sabbath
Black Sabbath are an English heavy metal band, formed in Aston, Birmingham in 1969 by Ozzy Osbourne , Tony Iommi , Geezer Butler , and Bill Ward . The band has since experienced multiple line-up changes, with Tony Iommi the only constant presence in the band through the years. A total of 22...
forged what would eventually become the heavy metal
Heavy metal music
Heavy metal is a genre of rock music that developed in the late 1960s and early 1970s, largely in the Midlands of the United Kingdom and the United States...
sound through a combined use of high volumes and heavy distortion.
Theory and circuits
The word distortion literally refers to any modification or addition to the wave form of a signal by any kind of equipment. In the context of music amplification distortion is equated with clippingClipping (audio)
Clipping is a form of waveform distortion that occurs when an amplifier is overdriven and attempts to deliver an output voltage or current beyond its maximum capability...
.
Clipping is a non-linear process that produces frequencies
Frequency
Frequency is the number of occurrences of a repeating event per unit time. It is also referred to as temporal frequency.The period is the duration of one cycle in a repeating event, so the period is the reciprocal of the frequency...
not originally present in the audio signal
Audio signal
An audio signal is an analog representation of sound, typically as an electrical voltage. Audio signals may be synthesized directly, or may originate at a transducer such as a microphone, musical instrument pickup, phonograph cartridge, or tape head. Loudspeakers or headphones convert an electrical...
. These frequencies can either be "harmonic
Harmonic
A harmonic of a wave is a component frequency of the signal that is an integer multiple of the fundamental frequency, i.e. if the fundamental frequency is f, the harmonics have frequencies 2f, 3f, 4f, . . . etc. The harmonics have the property that they are all periodic at the fundamental...
", meaning they are whole number multiples of the signal's original frequencies, or "inharmonic", meaning dissonant
Consonance and dissonance
In music, a consonance is a harmony, chord, or interval considered stable, as opposed to a dissonance , which is considered to be unstable...
odd-order overtones. Harmonic distortion produces harmonically related overtones while intermodulation distortion produces inharmonic overtones.
"Soft clipping" gradually flattens the peaks of a signal and de-emphasizes higher odd harmonics. "Hard clipping" flattens peaks abruptly, resulting in harsh-sounding, high amplitude
Amplitude
Amplitude is the magnitude of change in the oscillating variable with each oscillation within an oscillating system. For example, sound waves in air are oscillations in atmospheric pressure and their amplitudes are proportional to the change in pressure during one oscillation...
odd harmonics.
Distortion circuits distort a signal before it reaches the main amplifier. Overdrive circuits do not create distortion themselves but rather boost signals to levels that cause distortion to occur at the main amplifier's front end stage.
Valve overdrive
Vacuum tubeVacuum tube
In electronics, a vacuum tube, electron tube , or thermionic valve , reduced to simply "tube" or "valve" in everyday parlance, is a device that relies on the flow of electric current through a vacuum...
or “valve” distortion is achieved by “overdriving” the valves in an amplifier.Valve amplifiers--particularly those using triode
Triode
A triode is an electronic amplification device having three active electrodes. The term most commonly applies to a vacuum tube with three elements: the filament or cathode, the grid, and the plate or anode. The triode vacuum tube was the first electronic amplification device...
s--tend to produce asymmetric soft clipping that creates "warm"-sounding even-order harmonics.
A basic triode valve contains a cathode, a plate and a grid. When a positive voltage
Voltage
Voltage, otherwise known as electrical potential difference or electric tension is the difference in electric potential between two points — or the difference in electric potential energy per unit charge between two points...
is applied to the plate, a current
Electric current
Electric current is a flow of electric charge through a medium.This charge is typically carried by moving electrons in a conductor such as wire...
of negatively charged electrons flows to it from the heated cathode through the grid. This increases the voltage of the audio signal, 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 1. the saturation region: the voltages at which plate current stops responding to positive increases in grid voltage and 2. 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 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 amplifiers incorporate discrete transistorTransistor
A transistor is a semiconductor device used to amplify and switch electronic signals and power. It is composed of a semiconductor material with at least three terminals for connection to an external circuit. A voltage or current applied to one pair of the transistor's terminals changes the current...
s and/or op amps and are prone to produce hard clipping and symmetrical distortion when overdriven. This adds additional high-amplitude odd harmonics, creating a "dirty" or "gritty" tone. Electronically, this is usually achieved by either amplifying the signal to a point where it must be clipped to the supply rails, or by clipping the signal across 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.
Guitar distortion 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.Overdrive/distortion pedals
Because they are often designed to operate with low voltages (such as 9 volt batteries), overdrive and distortion pedals typically use transistors to generate distortion. Classic examples include the Ibanez Tube ScreamerIbanez Tube Screamer
The Ibanez Tube Screamer is a guitar overdrive pedal, made by Ibanez. The pedal has a characteristic mid-boosted tone popular with blues players...
and the Electro-Harmonix Big Muff
Big Muff
The Big Muff is a fuzzbox produced in New York City by the Electro-Harmonix company, along with their Russian sister company Sovtek, primarily for use with the electric guitar...
.
To reduce unwanted dissonance, single notes and simple power chord
Power chord
In music, a power chord is a chord consisting of only the root note of the chord and the fifth interval, usually played on electric guitar, and typically through an amplification process that imparts distortion...
s (root, fifth, and octave) are often used when using fuzzboxes, rather than triads (root, third, and fifth) or four-note chords (root, third, fifth, and seventh).
Pre-amplifier distortion
The pre-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 equalizationEqualization (audio)
Equalization is the process commonly used in sound recording and reproduction to alter the frequency response of an audio system using linear filters. Most hi-fi equipment uses relatively simple filters to make bass and treble adjustments. Graphic and parametric equalizers have much more...
and gain
Gain
In electronics, gain is a measure of the ability of a circuit to increase the power or amplitude of a signal from the input to the output. It is usually defined as the mean ratio of the signal output of a system to the signal input of the same system. It may also be defined on a logarithmic scale,...
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, many amps featured a "master volume" control, an adjustable attenuator between the preamp section and the power amp. When the preamp is set up to generate high distortion levels the master volume can be used to divert most of the resulting signal away from the power valves, keeping the output volume at manageable levels.
Power amplifier distortion
Push-pull output
A push–pull output is a type of electronic circuit that can drive either a positive or a negative current into a load. Push–pull outputs are present in TTL and CMOS digital logic circuits and in some types of amplifiers, and are usually realized as a complementary pair of transistors, one...
configuration in their power section, with matched pairs of tubes driving the output transformer. Power amplifier distortion is 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, allow the player to generate power valve distortion without excessive volume. These include built-in or separate power attenuators
Power attenuator (guitar)
In conjunction with an electric guitar amplifier, a power attenuator is used to divert and dissipate some or all of the amplifier's excess or unneeded power in order to reduce the volume of sound produced by the speaker.- Explanation :...
and power-supply-based power attenuation. Lower-power valve amps (such as a quarter-watt or less), speaker isolation cabinets
Isolation cabinet (guitar)
The characteristic sound of a tube guitar amplifier as heard on the majority of professional recordings is achieved by playing the amplifier at high volumes, and using one or more microphones to capture the sound. Turning the volume up causes the pre-amplifier to drive the power amplifier into...
, 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
19-inch rack
A 19-inch rack is a standardized frame or enclosure for mounting multiple equipment modules. Each module has a front panel that is wide, including edges or ears that protrude on each side which allow the module to be fastened to the rack frame with screws.-Overview and history:Equipment designed...
preamp, a rackmount valve power amp, and a rackmount dummy load
Dummy load
A dummy load is a device used to simulate an electrical load, usually for testing purposes.-Radio:In radio this device is also known as a dummy antenna or a radio frequency termination. It is a device used in place of an antenna to aid in testing a radio transmitter...
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
12AX7 is a miniature dual triode vacuum tube with high voltage gain. It was developed around 1946 by RCA engineers in Harrison, New Jersey, under developmental number A-4522. It was released for public sale under the 12AX7 identifier on September 15, 1947. The 12AX7 was originally intended as...
in a power-valve circuit configuration (as in the Stephenson's Stage Hog), or use a conventional power valve, such as the EL84
EL84
The EL84 is a vacuum tube of the power pentode type. It has a 9 pin Noval base and is found mainly in the final output stages of amplification circuits, most commonly now in guitar amplifiers, but originally in radios and many other devices of the pre-transistor era.It was developed to eliminate...
(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.
A Direct Inject
DI unit
A DI unit, DI box, Direct Box, or simply DI , is a device typically used in recording studios to connect a high-impedance, line level, unbalanced output signal to a low-impedance microphone level balanced input, usually via XLR connector...
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 transformerTransformer
A transformer is a device that transfers electrical energy from one circuit to another through inductively coupled conductors—the transformer's coils. A varying current in the first or primary winding creates a varying magnetic flux in the transformer's core and thus a varying magnetic field...
sits between the power valves and the speaker, serving to match impedance
Electrical impedance
Electrical impedance, or simply impedance, is the measure of the opposition that an electrical circuit presents to the passage of a current when a voltage is applied. In quantitative terms, it is the complex ratio of the voltage to the current in an alternating current circuit...
. When a transformer's ferromagnetic core becomes electromagnetically saturated, it will clip symmetrically. This adds additional odd-order distortion to the signal delivered to the speakers.
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 anodeAnode
An anode is an electrode through which electric current flows into a polarized electrical device. Mnemonic: ACID ....
supply was simply a rectifier
Rectifier
A rectifier is an electrical device that converts alternating current , which periodically reverses direction, to direct current , which flows in only one direction. The process is known as rectification...
, an inductor and a capacitor
Capacitor
A capacitor is a passive two-terminal electrical component used to store energy in an electric field. The forms of practical capacitors vary widely, but all contain at least two electrical conductors separated by a dielectric ; for example, one common construction consists of metal foils separated...
. When the valve amplifier was operated at high volume
Volume
Volume is the quantity of three-dimensional space enclosed by some closed boundary, for example, the space that a substance or shape occupies or contains....
, the power supply
Power supply
A power supply is a device that supplies electrical energy to one or more electric loads. The term is most commonly applied to devices that convert one form of electrical energy to another, though it may also refer to devices that convert another form of energy to electrical energy...
voltage
Voltage
Voltage, otherwise known as electrical potential difference or electric tension is the difference in electric potential between two points — or the difference in electric potential energy per unit charge between two points...
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
Rectifier
A rectifier is an electrical device that converts alternating current , which periodically reverses direction, to direct current , which flows in only one direction. The process is known as rectification...
valve. In a Class A amplifier, current draw is constant, so sag does not occur.
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
Sustain
In music, sustain is a parameter of musical sound over time. As its name implies, it denotes the period of time during which the sound remains before it becomes inaudible, or silent.Additionally, sustain is the third of the four segments in an ADSR envelope...
. 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 are designed differently from high fidelity stereo speakers or PA system speakers. While hi-fi and PA speakers are designed to reproduce the sound with as little distortion as possible, guitar speakers are usually designed so that they will shape or colour 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 lots of 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 processingDigital signal processing
Digital signal processing is concerned with the representation of discrete time signals by a sequence of numbers or symbols and the processing of these signals. Digital signal processing and analog signal processing are subfields of signal processing...
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 preampPreamplifier
A preamplifier is an electronic amplifier that prepares a small electrical signal for further amplification or processing. A preamplifier is often placed close to the sensor to reduce the effects of noise and interference. It is used to boost the signal strength to drive the cable to the main...
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
Frequency response
Frequency response is the quantitative measure of the output spectrum of a system or device in response to a stimulus, and is used to characterize the dynamics of the system. It is a measure of magnitude and phase of the output as a function of frequency, in comparison to the input...
before and after each distortion stage. This dependency of distortion voicing on frequency response can be heard in the effect that a wah pedal
Wah-wah pedal
A wah-wah pedal is a type of guitar effects pedal that alters the tone of the signal to create a distinctive effect, mimicking the human voice...
has on the subsequent distortion stage, or by using tone controls built in to 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.
See also
- DistortionDistortionA distortion is the alteration of the original shape of an object, image, sound, waveform or other form of information or representation. Distortion is usually unwanted, and often many methods are employed to minimize it in practice...
- Effects unitEffects unitEffects units are electronic devices that alter how a musical instrument or other audio source sounds. Some effects subtly "color" a sound, while others transform it dramatically. Effects are used during live performances or in the studio, typically with electric guitar, keyboard and bass...
- Guitar pedalboardGuitar pedalboardA guitar pedalboard is a flat board or panel which 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, in order to power a number of different pedals. Pedalboards assist the player in...
- Valve sound
- Guitar effects
- Effects pedal
- Guitar amplifierGuitar amplifierA guitar amplifier is an electronic amplifier designed to make the signal of an electric or acoustic guitar louder so that it will produce sound through a loudspeaker...
External links
- A Musical Distortion Primer (R.G. Keen) Article on the physics of distortion and a round-up of electronic techniques
- Guitar Distortion 101 Article on the physics of distortion, relationship of waveforms and harmonics
- Amptone.com- 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 to help readers learn to build their own guitar amps.
- Fuzz Central - Lots of Schematics and Fuzz Pedals
- History and Photos of Vintage Fuzz Pedals.
- Electro-Harmonix: Big Muff Pi
- Electro-Harmonix: Distortion, Fuzz, Overdrive effects pedals
- Tons of Tones !! : Technical site with information on distortion stages in Guitar Amplifier Models and Effect boxes
- Gibson Maestro Fuzz-Tone FZ-1 patent