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Effects are produced by modifying a signal in some way − usually in a way that improves the interest or "fullness" of the sound. This page describes some of the more commonly used effects.

The devices used to produce effects as part of a PA system are usually referred to as effects units or effects processors. Some models of mixer include one or more onboard effects processors, usually accessed via specific Aux Send controls. Floor-standing effects units used on-stage by musicians are usually referred to as pedals.

Effects may be applied to individual mixer channels, to audio groups or to entire mixes. For information on how outboard effects units may be connected into a system, please see the glossary entries for Serial effects unit and Parallel effects unit.

Note that this page does not include descriptions of dynamics processors such as compressors, expanders, limiters, noise gates or de-essers − see their respective glossary entries.


PA Effects Processors

The effects facilities used as part of a PA system are most commonly either stand-alone digital multi-functional units or are facilities built into a mixer. In either case, they are usually capable of producing most of the effects described below. Some facilities are able to produce several effects at the same time, in combination. In particular, many are able to provide all the common delay-based effects (reverberation, echo, delay, chorus, phase and flange). However, some sound engineers prefer to use stand-alone units that are dedicated to (or that specialise in) a particular type of effect, e.g. reverberation. Most stand-alone units are designed to be housed in 19 inch rack systems.


Usually referred to as 'reverb', this is an effect which simulates the ability of a room to cause a sound to die away slowly when the source of the sound ceases abruptly. Reverb units are useful in reducing the 'dryness' of a sound.

As rooms differ in the manner and degree to which they exhibit this effect, such effect units usually provide some control over the type and extent of the reverb effect which they produce. The more sophisticated digital units now available generally allow selection from a number of reverb types, for example types simulating various different sizes of room and types simulating the old analogue reverb effects such as spring-line and plate units.

Gated reverb is an effect which has the facility to automatically cut off the reverberation effect when the input signal falls below a specific level.


This is an effect which simulates a natural echoing of the sound, or which provides an artificial effect of a similar nature. Most units have the ability to provide a single echo or multiple echoes. See also Delay.


Delay is in principle the same effect as echo, because an echo is a delayed (and, usually, somewhat modified) copy of the original sound. Such a unit may also be used to provide a delayed version of a signal to 'secondary' speakers which are situated some distance in front of the main speakers (in a very large hall, or outdoors); this enables the sound heard from the secondary speakers to be synchronised with the sound heard from the main speakers − the latter having been delayed in travelling through the air to reach the location of the secondary speakers. Approximately 30 milliseconds of delay is required per 10 metres of distance between the main and secondary speakers (see Speed of sound).


This is an effect which modifies a signal in such as manner as to simulate the presence of several additional sources of the same (or similar) sound, all operating in unison − as in "a chorus of voices".


This is an effect that is sometimes used with guitars to improve the 'interest' of the sound. It may be adjusted to give a wide range of effects, a common one being a slow 'sweeping' sound.


This is similar to a more extreme version of the phase effect; a rather harsh 'sweeping' effect used with electric guitars to help give a 'heavy metal' type of sound, and for other 'special effects' purposes. (It gained its name from the fact that it was originally produced by mixing the sound with a tape-recorded version of it that was slowed down by means of friction applied to the flanges of the tape spools.)


Generally used only with electric guitars, an effect that simulates a distorting guitar amplifier. Previously known as 'fuzz'.


Generally used only with electric guitars, a more subtle version of the distortion effect, less rich in the higher harmonics. It simulates an overdriven guitar amplifier − specifically the softer clipping that would typically occur in an overdriven valve output stage.

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This page last updated 07-Jun-2019.