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An acoustic guitar is not dependent on any external device for amplification. The shape and resonance of the guitar itself creates acoustic amplification. However, the un-amplified guitar is not a loud instrument. It cannot compete with other instruments commonly found in bands and orchestras, in terms of sheer audible volume. Many acoustic guitars are available today with built-in electronics and power to enable amplification.
There are several subcategories within the acoustic guitar group: steel string guitars, which includes the flat top, or "folk" guitar, the closely related twelve string guitar, and the arch top guitar. A recent arrival in the acoustic guitar group is the acoustic bass guitar, similar in tuning to the electric bass.
The Electric Guitar
An electric guitar is a type of guitar that uses electronic pickups to convert the vibration of its steel-cored strings into electrical current. The signal may be electrically altered to achieve various tonal effects prior to being fed into an amplifier, which produces the final sound which can be either an electrical sound or an acoustic sound. Distortion, equalization, or other effects can change the sound that is emitted from the amplifier.
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The electric guitar is used extensively in many popular styles of music, including almost all genres of rock and roll, metal, country music, pop music, jazz, blues, and even contemporary classical music. Its distinctive sound and intimate association with many legendary internationally-famous musicians has made it the signature instrument of late twentieth-century music. Specialized steel guitars, although they are also electric instruments descended from the guitar, are normally not considered electric guitars but rather as a separate instrument. This distinction has important consequences on claims of priority in the history of the electric guitar.
Solid-Body Electric Guitars
Solid body electric guitars are guitars that have no hole for sound or internal cavity to accommodate vibration. They are generally made of hardwood with a lacquer coating and have 6 steel strings. The sound that is audible in music featuring electric guitars is produced by pickups on the guitar which convert the string vibrations into an electrical signal. The signal is then fed to an amplifier and speakers.
Hollow-Body Electric Guitars
These guitars have a hollow body and electronic pickups mounted on its body. They work in a similar way to solid body electric guitars except that because the hollow body also vibrates, the pickup convert a combination of string and body vibration into an electrical signal
Electric-Acoustic Guitars
Some steel-string acoustic guitars are fitted with pickups purely as an alternative to using a separate microphone. They may also be fitted with a piezoelectric pickup under the bridge, attached to the bridge mounting plate, or with a low mass microphone inside the body of the guitar that will convert the vibrations in the body into electronic signals, or even combinations of these types of pickups, with an integral mixer/pre-amp/graphic equalizer. These are called electric acoustic guitars, and are regarded as acoustic guitars rather than electric guitars because the pickups do not produce a signal directly from the vibration of the strings, but rather from the vibration of the guitar top or body. These should not be confused with hollow body electric guitars, which have pickups of the type found on solid body electric guitars.
Guitar Amplifiers
Guitar amplifiers come in two main forms. The combination amplifier contains the amplifier head and guitar speakers in a single unit. The amplifier head or amp head contains the electronic circuitry constituting the pre-amp, built-in effects processing, and power amp. In the other form, the amp head is separate from the speakers, and joined to them by cables. The separate amplifier is called an amplifier head, and is commonly placed on top of one or more loudspeaker enclosures. A separate amplifier head placed atop a guitar speaker enclosure or guitar speaker cabinet forms an amplifier stack or amp stack.
Some amplifiers used with electric guitars are solid state, because they are easy to repair, lighter-weight, and less expensive. Despite the drawbacks of vacuum tube amps, such as their heavy weight and the need to periodically pay to re-tube and re-bias the amp, many guitarists prefer the sound of vacuum tube amps, particularly in the genres of blues and rock. There are modern tube amplifier companies that are designing fixed-biased amps that require no tube biasing so long as the proper rating tube is used. There are also tube amps designed to make biasing very simple for the user. Some modern amps use a mixture of both tube and solid-state technologies, with 1960s vintage vacuum tubes next to integrated circuits. With the advent of microprocessors and digital signal processing in the late 1990s, modeling amps were developed that can simulate a variety of well-known amplifiers' vacuum tube sounds without necessarily using vacuum tubes. New amplifiers with special processors and software can emulate the sound of a classic amps almost perfectly, but due to the digital element of modeling the response of these amplifiers from the player's point of view is not quite the same. "Hard core" tube amp fans may not be able to tell the difference, in a blind auditory test, but will most always choose to play a tube amp because of its analog sensitivity.
Guitar Effects
Guitar effects are electronic devices that modify the tone, pitch, or sound of an electric guitar. Effects can be housed in effects pedals, guitar amplifiers, guitar amplifier simulation software, and rack-mount preamplifiers or processors. Electronic effects and signal processing form an important part of the electric guitar tone used in many genres, such as rock, pop, blues, and metal.
Guitar effects are also used with other instruments in rock, pop, blues, and metal, such as electronic keyboards or electric bass.
Distortion Pedals
Distortion is an important part of an electric guitar's sound in many genres, particularly for rock, hard rock, and metal. A distortion pedal takes a normal electric guitar signal and distorts the signal's waveform by "clipping" the signal. There are several different types of distortion effects, each with distinct sonic characteristics. These include regular distortion, overdrive, and "fuzz".
Although most distortion devices use solid-state circuitry, some "tube distortion" pedals are designed with preamplifier vacuum tubes. In some cases, tube distortion pedals use power tubes or a pre-amp tube used as a power tube driving a built-in "dummy load." Distortion pedals designed specifically for bass guitar are also available. Some distortion pedals include:
Overdrive Pedals
Some distortion effects provide an "overdrive" effect. Either by using a vacuum tube, or by using simulated tube modeling techniques, the top of the wave form is compressed, thus giving a smoother distorted signal than regular distortion effects. When an overdrive effect is used at a high setting, the sound's waveform can become clipped, which imparts a gritty or "dirty" tone, which sounds like a tube amplifier "driven" to its limit. Some overdrive pedals include:
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Boss SD-1
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Line 6 Crunchtone
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Power-Tube Pedals
A Power-Tube pedal contains a power tube and optional dummy load, or a pre-amp tube used as a power tube. This allows the device to produce power-tube distortion independently of volume; therefore, power-tube distortion can be used as an effects module in an effects chain. Some examples are:
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Stephenson Stage Hog
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Damage Control Demonizer
Power Attenuators
A Power Attenuator enables obtaining power-tube distortion independently of listening volume. A power attenuator is a dummy load placed between the guitar amplifier's power tubes and the guitar speaker, or a power-supply based circuit to reduce the plate voltage on the power tubes. Examples of power attenuators are:
Compressors
A compressor acts as an automatic volume control, progressively decreasing the output level as the incoming signal gets louder, and vice versa. It preserves the note's attack rather than silencing it as with an Envelope Volume pedal. This adjustment of the volume for the attack and tail of a note evens out the overall volume of an instrument. Compressors can also change the behavior of other effects, especially distortion. When applied to instruments with a normally short attack, such as drums or harpsichord, compression can drastically change the resulting sound. Some compressor pedals are:
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Boss CS-3
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Line 6 Constrictor
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T-Rex Engineering's CompNova
There are many other types of custom guitar effects boxes and pedals. It would be impossible to list all of the options available to guitarists. We can make a recommendation for the best effects brand in our opinion: Line 6.
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