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Distortion and overdrive are forms of audio signal processing used to alter the sound of amplified electric musical instruments, usually by increasing their gain, producing a "fuzzy", "growling", or "gritty" tone. Distortion is most commonly used with the electric guitar, but may be used with other instruments, such as bass guitar, electric piano, synthesizer, and Hammond organ. Guitarists playing Chicago blues originally obtained an overdriven sound by turning up their vacuum tube-powered to high volumes, which caused the signal to distort. Other ways to produce distortion have been developed since the 1960s, such as distortion effects unit. The growling tone of a distorted electric guitar is a key part of many genres, including blues and many rock music genres, notably hard rock, punk rock, hardcore punk, acid rock, grunge and heavy metal music, while the use of distorted bass has been essential in a genre of hip hop music and alternative hip hop known as "SoundCloud rap".
The effects alter the instrument sound by clipping the signal (pushing it past its maximum, which shears off the peaks and troughs of the signal waves), adding sustain and harmonic and inharmonic , 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), which has been emulated since the 1960s by a number of "fuzzbox" effects pedals.
Distortion, overdrive, and fuzz can be produced by effects pedals, rackmounts, , (a potentially speaker-blowing approach), and (since the 2000s) digital amplifier modeling devices and audio software. These effects are used with , (fuzz bass), electronic keyboards, and more rarely, special effects 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 to amplify vocals or when playing back prerecorded music.
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 song "Rocket 88", where guitarist Willie Kizart used a vacuum tube amplifier that had a speaker cone slightly damaged in transport. Electric guitarists began "doctoring" amplifiers and speakers to emulate this form of distortion.
Electric blues guitarist Willie Johnson of Howlin' Wolf′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 song "The Things That I Used to Do" (1953). Chuck Berry's 1955 classic "Maybellene" features a guitar solo with warm created by his small valve amplifier. Pat Hare produced heavily distorted on his electric guitar for records such as James Cotton's "Cotton Crop Blues" (1954) as well as his "I'm Gonna Murder My Baby" (1954), creating "a grittier, nastier, more ferocious electric guitar sound", accomplished by turning the volume knob on his amplifier "all the way to the right until the speaker was screaming."Robert Palmer, "Church of the Sonic Guitar", pp. 13-38 in Anthony DeCurtis, Present Tense, Duke University Press, 1992, pp. 24-27. .
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. 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 on releasing the sessions, arguing that "that guitar sounds like a nice horn section".
In the late 1950s, guitarist Link Wray began 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 , "Rumble" and "Rawhide".
Shortly thereafter, the American instrumental rock band The Ventures asked their friend, session musician and electronics enthusiast 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 of The Kinks used a razor blade to slash his speaker cones for the band's single "You Really Got Me".Walser 1993, p. 9
In May 1965, Keith Richards 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 Rush Pepbox (1964), 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 to play fuzz bass on "Think for Yourself" and other Beatles recordings.
In 1966, Jim Marshall of the Marshall Amplification company began modifying the electronic circuitry of his amplifiers so as to achieve a "brighter, louder" sound and fuller distortion capabilities.
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 Frequency not originally present in the audio signal. These frequencies can be harmonic, meaning they are whole number multiples of one of the signal's original frequencies, or "inharmonic" overtones, 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 .
"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 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 the amplifier.Product names may not accurately reflect the 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.
A basic triode valve (tube) contains a cathode, a plate, and a grid. When a positive voltage is applied to the plate, a Electric 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, and 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
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" 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.
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 is lowered, keeping the output volume at manageable levels.
Analog effects 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, , and diodes. Classic examples of distortion effects pedals include the Boss Corporation (overdrives), the Ibanez Tube Screamer (an overdrive), the Electro-Harmonix Big Muff Pi (a fuzz box), and the Pro Co RAT (a distortion).
Although the terms are sometimes used interchangeably, guitarists and manufacturers typically distinguish between overdrive, distortion, and fuzz. Generally, overdrive pedals aim to simulate the sound of a tube amplifier pushed into saturation, providing a dynamic response to picking intensity. The first effects pedals strictly marketed as "overdrive" were aimed at players who wanted the characteristic "amp breakup" tone without having to play at very high volume levels or risk damaging their equipment. Distortion pedals produce a coloured, more compressed and heavily saturated tone, less dependent on playing dynamics; as such, they are often paired with relatively clean amplifiers so that the pedal provides the bulk of the distortion. Fuzz pedals, which date back to the 1960s, use extreme clipping to generate a buzzy, harmonically rich sound that can resemble a square wave.
Classic examples of overdrive pedals include the Ibanez Tube Screamer and the Boss Corporation OD series. Distortion pedals include the Pro Co RAT and Boss DS-1, which both found use in heavier guitar based music like grunge and alternative rock, while fuzz pedals like the Big Muff create a sustaining, harmonically rich sound.
Most distortion effects 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 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, guitarists (and keyboardists) using these effects may restrict their playing to single notes and simple "" (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 player (Hammond organs do 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; additionally, lighter overdrive allows more control of dynamics.
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 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 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. Power amplifier distortion may damage speakers.
A DI unit 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.
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 much clean headroom, while others are designed to break up early to deliver grit and growl.
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.
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; use attenuation "pads" (a button on audio console channel strips, DI unit and some ); and use electronic audio compressor effects and limiters to prevent sudden volume peaks from vocal mics causing unwanted distortion.
Though some bass guitar 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 jazz and traditional country music, 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 or use keyboard amplifiers that are designed to reproduce the audio signal with as little distortion as possible. The exceptions with keyboards are the Hammond organ 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 or fiddle in a Folk music or Bluegrass music style.
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