Distortion effects create "warm", "dirty" and "fuzzy" sounds by compressing the peaks of a musical instrument's sound wave and adding overtones. 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, speakers and more recently, digital amplifier modeling devices and software. The process of altering an audio signal’s wave form is called “clipping”. 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.
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 recording of "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. rock band The Ventures recorded "2000 Pound Bee" using the first fuzzbox.]] 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.
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. 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.
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.
Category:Amplified instruments Category:Effects units Category:Electric guitars Category:Audio effects
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