Effects unit

From Academic Kids

Effects units are devices that affect the sound of an electric instrument when plugged in to the electrical signal path the instrument sends, most often an electric guitar or bass guitar. They can also be used on other instruments or sound sources, like the Rhodes Piano or standard MIDI keyboards, synths or even the human voice. While some effect units transform the sound completely, others just color the sound picture in a minor way.

An effects unit consists of one or more electronic devices which typically contain analog circuitry for processing audio signals, similar to that found in music synthesizers, for example active and passive filters, envelope followers, voltage-controlled oscillators, or digital delays.

Effects units are packaged by their manufacturers, and used by musicians, in various sizes, the most common of which are the stomp-box and the rack-mount unit. A "Stomp box" is a metal box, containing the circuitry, which is placed on the floor in front of the musician and connected in line with, say, the guitar cord. The box is typically controlled by one or more foot-pedal on-off switches and typically contains only one or two effects. A second type of effects unit may contain the identical electronic circuit, but is mounted in a standard 19" equipment rack. Usually, however, rack-mount effects units contain several different types of effects. They are typically controlled by knobs or switches on the front panel, and often by a MIDI digital control interface. "Off-boards" are used by musicians who prefer multiple stomp-boxes; these may be simply pieces of plywood with several stomp-box units fastened to the plywood and connected in series. Rackmounted effects or off-boards can combine several effects in one unit, and can include analog controls such as pedals or knobs.

Modern desktop and notebook computers often have sound processing capabilities that rival commercially available effects boxes. Some can process sound through VST-plugins. With a decent sound card, you could play any instrument through the computer, emulating any effects unit or even an amplifier in a convincing way. Many VST-plugins are freely downloadable from the World Wide Web.


Types of effects


The gain of the amplifier is varied to reduce the dynamic range of the signal.
Tremolo produces a periodic variation in the amplitude (volume) of the note. A sine wave applied as input to a voltage-controlled amplifier produces this effect.


Overdrive and distortion
The signal is cranked up past the limits of the amplifier, resulting in clipping. Example: Guitar on Spirit in the Sky by Norman Greenbaum. (see Fuzzbox)
Ring modulation


First used by Les Paul, e.g. I'm Forever Blowing Bubbles. (Modern digital delay units, the first of which was the Eventide Harmonizer, involve sound waves being converted from analog to digital signals, and clocked through large banks of RAM memory. Paul achieved time delay by stretching audiotape between two reel-to-reel tape decks spaced several feet apart.)
Uses delays to simulate an echo
Usually short delays to simulate more than one person playing at a time
Uses very short variable delays to cause a changing comb filter effect


Pitch shifter 
Also introduced by the Harmonizer which has a knob on the front to "change your pitch up." First used on Itchycoo Park by Small Faces.
Vibrato refers to a variation in frequency of a note, for example as an opera singer holding one note for a long time will varies the frequency up and down. A sine wave applied as input to a voltage-controlled oscillator produces this effect.
Guitarists often use the terms "vibrato" and "tremolo" inconsistently. A so-called vibrato unit in a guitar amplifier actually produces tremolo, while a tremolo arm on a guitar produces vibrato. However, finger vibrato is genuine vibrato. See Electric guitar, tremolo, vibrato.

Other specific effects

It simulates a fretless guitar
Acoustic guitar simulator
Rotary speaker
Pickup simulation 
Simulates either a single-coil pickup if the musician has a humbucker or vice-versa
Ambience modelling
Cabinet modelling
Amplifier modelling

Notable manufacturers

See also


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