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There are numerous effects options available to the guitarist, especially the electric guitarist. This question is intended to gather and cultivate a set of answers to questions in the form of:

What is insert guitar effect here for? How does it sound?

Please create a single answer for each effect and feel free to edit answers to make them more comprehensive and / or accurate.

It might also make each answer more useful if there were an example listed of a good representative recording of the effect.

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I am creating some "stub" answers intended to be improved and updated by those more expert than I. This question is a result of discussion in the comments of another question. –  gomad Apr 29 '11 at 20:28
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Converting to Community Wiki, this is quite a wiki based question. –  Ali Maxwell Apr 29 '11 at 20:53
    
Thanks, Alistair! I figured this was destined to be CW, but some people are saying that CW is deprecated now, so I didn't want to put that in the question itself. –  gomad Apr 29 '11 at 21:52
    
could we also make tags fro these that have this info? maybe effects-compression, or more hierarchicallike: effects-modulation-chorus. –  InternalConspiracy Apr 30 '11 at 4:43
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It would be extremely useful to have at least one example of a good example of each effect and, where appropriate, of some combined effects. That way, perhaps people could work backwards from "I want to sound like insert guitarist here. –  Steve Ross Nov 26 '11 at 0:03

19 Answers 19

Gate / Noise Cancellation

A gate filters silences the output if the input signal is quieter than a configured level.

Noise Cancellation is a common application of a gate. By setting the cutoff level to a level that is louder than the buzz and noise when no note is being played, yet quieter than the quietest note that you will play, it suppresses the buzz and noise when you are not playing.

A poor quality device, or one with the cutoff set too high, can cause notes that you wanted to be heard, to be suppressed.

More sophisticated gates will allow you to adjust the response curve -- how the volume ramps up around the cutoff point -- and its response time -- how quickly it turns the volume up when it detects a loud enough signal.

It can sometimes be useful to trigger the gate using a different signal from the one it is gating. For example you might have a guitar line pulsate in time to a drum.

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One type of "effect" I've thought would be useful to have in a multi-pedal, though I've not seen it, would be to have a configurable automatic gain control (level compression) which would be applied before a distortion effect, followed by a gain adjustment after the distortion which would undo some or all of the effect of the previous AGC. For example, things might be set up so that playing at a level of -20dBm would boost the signal by 21dB (clipping slightly) and then reduce volume by 20dB, while playing at -10dBm would boost by 12dB (clipping a bit more) and then reduce by 12dB. –  supercat Apr 30 '13 at 22:01
    
As it is, it seems most distortion effects have a fairly small "sweet spot" of levels where they work well, and cause dynamics in one's playing to translate primarily into changes in timbre rather than volume. –  supercat Apr 30 '13 at 22:02

Delay

Delay is an effect in itself, and also the basis of some of the other effects1.

Delay is simply the effect of playing the input signal some time later than it was fed into the device. Delays can be as short as a couple of milliseconds, as long as a bar, or more.

Usually, but not always, the delayed signal is combined with the original signal, because players want to hear what they play the moment they play it. Often it is mixed such that the original signal is louder than the delayed signal.

Originally delay was achieved using a loop of magnetic tape - first on improvised arrangements with a reel-to-reel recorder, and later on dedicated machines. The tape would pass through a record head, then a playback head, then an erase head. The timing of the delay could be adjusted by moving the heads, or changing the speed of the tape. Tape adds its own colour to sound, so the echo would have that added warmth.

Later, analogue circuits were developed to achieve delay, first with tubes, then with transistors, each of these adding a certain colour to the delayed signal.

Digital delay inevitably followed, and of course now we have digital delays which attempt to model the effects of the analogue devices of history.

When the delay is very short, the signals tend to interfere with each other in interesting ways -- see Phaser and Flanger.

When the delay is slightly longer -- close enough to still be considered "on the beat" -- you get what is known as doubling echo. This sounds similar to having two instruments playing in unison. The delay is simulating the slight difference in timing two human players would have.

Chorus is a variation on doubling echo, in which the delay varies -- the tape loop speeding up and slowing down continually. This means your "virtual" duet partner is slightly off time by a varying degree, and also slightly off-pitch by a varying degree. See the separate answer on chorus.

When the delay is longer still -- long enough that you begin to be able to hear it as a distinct note -- this is known as slapback echo. It's an effect frequently heard in rockabilly guitar, and the "skanking" guitar parts of reggae.

When the delay is even longer, delay becomes a melodic tool -- you are effectively duetting with your earlier self. Many U2 songs, e.g. "Where the Streets Have No Name", are built around this effect.

It's common to feed the delayed signal back into itself, so that you get echoes of echoes, each (usually) quieter than the last.

Using this fed-back delay on short delays creates a crude reverb effect. With longer delays it becomes a rhythmic/melodic effect. For example it's common to add delay to parts of drum patterns to create a complex rhythm part.

With analogue delay (and simulations thereof), each subsequent echo is not only quieter, but also more distorted. Dub reggae tracks often make prominent use of this effect -- look out for the effect where the engineer momentarily turns a knob so that the echoes get louder instead of quieter, surging and distorting, before he turns it back down again so they can die away.


1Note that no signal processing is instantaneous, so every effect adds some small delay. For digital effects this is the measurable and sometimes notable latency of something millisecond-ish (hopefully not more than a few ms). In simple analogue effects like distortion it's at most in the nanosecond range and basically neglectable. Any equaliser/filter component also introduce phase delay, which can be interpreted as delaying various frequencies by different amounts; but this too is normally not noticable and works quite differently from a digital delay.

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Boost

Boost is an effect which boosts the volume of an input signal, in order to assure that the amplifier is driven beyond its regular dynamic range and thus will produce clipping and thereby distortion. Boosts are very useful for tube amp players who wish to increase the gain on their amplifier without having to modify the tone the way a traditional overdrive or fuzz pedal would. A boost is often measured by how transparent it is--although there are some on the market (such as the Katana by Keeley and the EarthTone by NOC3) that employ JFET designs to produce additional "dirt" when engaged to add a subtle fattening effect to the boost.

Note that any pedal with a volume knob that past unity gain* can function as a boost. For example, turning a volume control past unity gain on something as benign as a Chorus pedal will produce additional distortion from a tube based amplifier.

*Unity gain is the position on a volume control where the input level is equal to the output level. Typically this works out to be at about 1 O'clock on most pedals.

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Octave

Octave effects take the input signal and produce synthesized tones that are one or more octaves above or below it. They can be blended in with the input signal to harmonize with it in real time. The effect can be synthesized by monitoring the waveform of the input and multiplying or dividing the observed frequency by, for example, 2 (to go up or down an octave) or 4 (to go up or down two octaves). This takes advantage of the fact that tones that are an octave apart have a 2:1 frequency relationship; the frequency of the tone one octave higher than a root tone is always double the frequency of the root tone.

Because they're acting on the monitored waveform, octave effects sound best on, and are meant to be used for, single-note riffs. For this reason, they are popular with many bass guitarists and soloists.

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Chorus

Chorus is an effect that copies the input signal passed to it, modulates the pitch of it by some configured parameters, and stacks it back on top of the original signal.

Originally, the motivation would have been to simulate the sound of two singers -- the second being very slightly delayed by a gently varying amount, and at not precisely the same pitch, by a gently varying amount.

However once the technology had been created, people experimented with the parameters, and by varying the speed faster, and by a greater degree, achieved a distinctive sound all of its own.

Choruses (Chori?) come in mono, stereo, and true stereo versions, and a good one will provide lots of control across the depth and speed of the modulation desired. In the case of a mono unit, the aggregate tone produced by the circuit is flattened and passed through a single jack, where as a stereo (sic) unit will pass wet and dry signals through different jacks. A true stereo chorus unit will produce a true stereo signal, where the effect is mixed properly into left and right channels.

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Reverb

Reverb is the effect of playing a sound in an enclosed space, or a simulation of that effect. The sound travels from the source to your ear directly, but it also bounces off surfaces in the room to reach your ear, each reflection arriving at a different time, with different frequencies lost.

If you play with no effects, in a room full of soft surfaces which absorb sound, it can sound very lifeless and unnatural. Indeed, such a room is described as acoustically "dead".

If you play in a room full of hard surfaces, the reverberations add interest and colour to the sound. Such a room is often described as "lively". However, taken too far, the reverberations can overpower the original sound and make everything sound mushy.

The ideal is to find the sweet spot between these two extremes.

Clearly, when playing live rather than recording, the room you are in will create its own reverb. However it is still often desirable to apply artificial reverb as an artistic effect. Think of the lead guitar in Chris Isaac's Wicked Game; drenched in reverb.

Chamber reverb is how "artificial" reverb was originally achieved. The signal is played through a loudspeaker in a dedicated, soundproofed room, and picked up by microphones in that room. Chambers like this are a feature of high-end recording studios.

Plate reverb and spring reverb were the first attempts to simulate reverb in a portable device. The plate and the spring, respectively, are made of metal and attached to a transducer. The signal is fed to the transducer, which causes the plate or spring to vibrate. Reverberations bounce around the plate or spring. A pickup at the other end, converts the spring or plate's vibrations back into an electrical signal.

Plate and spring reverb, of course, are distant approximations of room reverb, but as with many artificial effects, they became popular in their own right.

Early Digital reverb used a large number of digital delays, at a mixture of volumes and timings.

Today, digital delays can simulate real rooms, and of course they also simulate plate reverb and spring reverb.

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Compressor/Limiter

Compression is used to reduce the dynamic range of a signal. It can be used at the top of the amplitude range, to reduce the volume of a specified range of inputs, or at the bottom of the amplitude range, to increase the volume of a specified range of inputs.

In the case where a compressor is used to reduce volume it may be referred to as a limiter.

A more in-depth description can be found on this question: What Does a Compressor Pedal Do?

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Fuzz

Fuzz gained much glory from the sixties and seventies when popularized by musicians such as Jimi Hendrix. Today, fuzz pedals have evolved into a staple for some bands and is capable of producing everything from a singing, warm sustain to a scratchy, velcro sound. The mainstay of a fuzz pedal's sound is produced by an electrical component called a transistor. Fuzz pedals today can be created from silicon transistors, or germanium transistors. Silicon is known to produce a slightly harsh or bright sound (some consider it sterile) while germanium typically accentuates the low end and produces a warmer sound. Just as extreme settings on a silicon fuzz pedal can easily produce a harsh, glass-like sound, extreme settings on a germanium transistor based fuzz can produce an overly warm, and muted tone.

One unique application of a fuzz pedal involves starving the pedal of voltage--which will produce a scratchy, velcro-like tone. This is desirable by some musicians because it is a highly unique sound and is often employed by more avant garde musicians. This sound can be achieved by purchasing a power supply with a sag output, or using a nearly dead battery, although the pedal won't last long when using that method.

Another application of a fuzz pedal is available when the user has control over the the amount of feedback signal routed back into the transistor loop while the pedal is engaged. By configuring the feedback to more sensitive levels, the pedal will feed back into itself causing oscillation*. As the pedal oscillates, certain frequencies will be produced, causing a singing sustained note without the guitarist playing anything at all. The player can consequently play over the note produced to cancel out the feedback loop, but once the player stops the pedal will feed back into itself producing the configured signal once again.

*The oscillation concept can be though of as exactly like a delay pedal set to infinite repeats. As the pedal feeds back into itself, the sound compounds; however unlike a delay pedal fuzz pedal oscillation is not additive.

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Distortion

One of more commonly known effects for musicians is distortion. It falls into the family of effects sometimes referred to as "dirt" boxes: Distortion, Overdrive, and Fuzz. In simple terms, it is cutting the top and bottom of the sound wave off using a technique known as "hard" clipping to create a more square shaped wave instead of the more natural sine wave formation. A solid explanation on the techniques and methods of creating different types of distortion can be found on Wikipedia.

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No offense, but I may edit this to remove the wiki reference and expand on what Distortion (more commonly referred to as overdrive) is. I sometimes feel dirty whenever I see a wiki link :D. –  Jduv May 3 '11 at 14:05
    
@Jduv - I can't imagine that he would take offense. Please update the answer - that's why this is CW, and is entirely in the spirit with which I asked the question! –  gomad May 3 '11 at 18:18
    
I like the wiki link, leave it in as Wiki is another collaborative source just like this site. –  JPM Oct 27 '11 at 17:18
    
Actually this can be merged with fuzz answer –  teodozjan Jul 11 '12 at 14:56
    
Agree - I was trying to work out what the difference between fuzz and distortion/overdrive is. They're both abouta wave getting squared owing to some degree of saturation. If there is a difference, maybe it's worth making that clearer ? I'd do this myself but i@m only familiar with the term distortion/overdrive. –  user2808054 Jul 15 at 8:52

Phaser and Flanger

Both Phaser and Flanger effects are "Comb Filters".

A comb filter combines a wave with a very slightly delayed version of itself, causing both constructive and destructive interference. The result is that some frequencies are boosted, and some are cut. A graph of the frequency response has evenly spaced spikes, hence the "comb".

In a flanger, the delay in the signal is equal for all frequencies, and is slowly varied. This causes the accentuated frequency to sweep up and down.

In a phaser, the delay is achieved by an "all pass filter", which delays some frequencies more than others. This creates an other-worldly "wooshy" effect.

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Pitch Pedal / Whammy Pedal

Although this might fit in the octaver pedal, it deserves a category of its own. This pedal raises or lowers the pitch of the incoming sound. Most models and emulation go from one octave below to two octave above. Lowering the pitch by an octave enables you to simulate dive-bombing without a floating tremolo for example.

The opposite, going up one or two octaves, is famously used by Tom Morelo (Audioslave's "Like a stone" solo, among others), Matthew bellamy ("Fury" and "Muscle Museum"), and Johnny Greenwood("Subterranean homesick alien"). Other famous users from the top of my head: Satriani, Buckethead, Steve Vai.

Although it's less frequently used, the Whammy pedal can go to intermediate intervals, minor second, fifth etc.

Harmonizer

This unit can play the harmony to any lead you're playing: it's fifth, or third. The difference with a whammy pedal is that it respect the interval of the scale you're in. Of course you'ld have to tell the unit the tonality and scale type before-hand.

Tremolo

Modulate the volume of the sound at a given rate and intensity.

Wha-wha/Auto-filter/Enveloppe filter

Those are basicaly moving low-pass filter or high-pass filter. It can either be controled by foot or by an enveloppe follower: the effect intensity is controlled by the intensity of your playing. Used mostly on guitar and in Funk, but also on keyboards or bass (RATM's "Calm like a bomb").

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Amp Simulator

Although it is not really an effect in the sense it changes the sound before it enters the speaker, it is found more and more by digital guitar effect units.

An amp simulator does what it says: it simulates a guitar amplifier, mimicing mostly famous guitar amps by adding a combination of effects mentioned earlier (like boost, distortion).

The sound output from an amp simulator can be used to be directed to a normal amplifier, PA system etc.

Some advantages of using an amp simulator are:

  • easy switching between different simulated guitar amps
  • usually cheaper than the original (let alone the sum of possible simulations)
  • effective at low volumes (some amplifiers only produce their best sounds when cranked up loud)
  • effective in 100% microphone-free applications -- can output direct to a mixing desk, DAW or PA.

The main disadvantage is that some people consider the simulated sounds inferior to a real amplifier.

When used in conjunction with a real guitar amplifier, there's a complicated interplay between the tone created by the real amp, atop the tone create by the simulation. It makes more sense to use amp simulation with a PA amp or a HiFi amp, designed to faithfully reproduce its input: the amp simulation provides tone; the real amp provides volume.

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I would argue against "The main disadvantage is the quality is not as good as the original". I think some of the current advanced units such as AxeFX II and Kemper Profiling Amp can sound essentially and practically indistinguishable from their source amp and may offer subjective improvements. –  cadmium Apr 29 '13 at 21:43
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Ok I will remove it ... I'm not a guitarist but keyboardist (sssh) –  Michel Keijzers Apr 30 '13 at 1:43

Looper

A looper pedal or "phrase looper" allows a performer to record and later replay a phrase or passage from a song. Loops can be created on the spot during a performance or they can be pre-recorded. Some units allow a performer to layer multiple loops. The first loop effects were created with reel-to-reel tape using a tape loop. High-end boutique tape loop effects are still used by some studios who want a vintage sound. Digital loop effects recreate this effect using an electronic memory.

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There's an obsolete recording technology using magnetic wire. I wonder if you could make a "tape looper" that uses a guitar string?! –  luser droog Jan 1 at 6:53

Envelope Filter

This effect gives a guitar that ska/reggae sound. It works by varying the cutoff frequency of a low-pass or bandpass filter (the same filter that's in a Wah-Wah effect, hence the Envelope Filter is also called an Auto-Wah) using an envelope follower which watches the signal for amplitude changes. So it wahs your attack, and then gives less and less wah as the signal attenuates. So the sound has a crunchier attack and the tone is very sensitive to varying dynamics.

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I don't know enough about the specifics to answer to its fullest but I'm pretty sure this is missing a lot, such as the filter part –  Basstickler Dec 30 '13 at 16:38
    
Thanks, @Basstickler. I read-up a little more and made some corrections. –  luser droog Dec 31 '13 at 6:50

Multi-Effects (Multi-FX or MFX unit)

A multi-effects unit can offer a broad range of effects in one unit, including Amp emulation and speaker simulation.

These effects are usually produced by digitizing the audio signal and using digital processing of the original effects produced by a Digital Signal Processor or DSP.

Generally several effects can be applied and these combinations of effects may be stored as patches. Groups of patches may also be stored as banks, depending on the limitations of the system.

Some units may have limits on the number of effects, often determined by the DSP processing power, or may allow only certain effects to be applied together. More advanced units may offer fewer practical limitations.

Multi-effects units can be used in conjunction with an amp, either before the amp signal, in the effects loop of an amp, or sometimes both (this is known as the 4 Cable Method or 4CM). However, many units may also act as a usb-interface to record or play through a computer, direct sound through xlr out, or simple headphone support for practice.

Examples of multi-effects units include:

  • Digitech RP series pedals
  • Digitech DSP rackmount units
  • Line6 PodHD series pedals and desktop units
  • Avid Eleven Rack rack mount unit
  • Fractal Audio AxeFX series rack mount unit
  • Kemper Profiling Amp series desktop and rackmount units
  • TC Electronics Nova system pedals
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Boss (by Roland) also make a great range of multi-effects boards too. Bit surprised to not see them listed here. –  user2808054 Jul 15 at 9:09

Wah-wah (or just "wah")

This is effectively a foot-operated parametric equialiser.

A frequency is determined normally by the position of a foot pedal. The input signal is boosted at, and around, this frequency, above the rest of the signal. As you move the pedal, the frequency being amplified changes up or down. The frequency range is set so that it sits well with a guitar, which in turn isn't hugely dissimilar to the human voice's frequency range.

The end result is that at the lower end of the the wah-wah's frequency you get a "wwwww" kind of effect and it transposes at the higher end to a "aaaaah" sound, hence the name.

The pedal rocks forward and backward like a see-saw as you rest your foot on it. Move the pedal to get the wah effect. On some pedals, there is a switch under the toe end to switch ceon straight-through (no effect) to using the wah effect. This means that when you switch it on, it's always in the "aaaa" position. You can hear this in some of Hendrix's work.

Others just detect that the pedal has moved, and switch the effect on. When you stop moving the pedal, it switches off.

On some wah pedals, the signal-with-effect ends up slightly louder than the original signal because a portion of it is being boosted. Other (normally more modern) ones cater for this by bringing the overall signal down a little when using the effect, so that you just get the effect and not extra output.

To hear a classic example of this effect, listen to the beginning of Hendrix's Voodoo Chile (slight return)

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Ring Modulator

Ring modulation takes two separate inputted signals and multiplies those signals. A ring modulator will typically take the input signal from an instrument and mix it with a second signal generated by an internal oscillator which you can vary the frequency of.

Moderate frequencies generate eerie, bell-like tones that sound awesome beneath oceans of reverb. Higher frequencies produce ear-shredding shrieks. Meanwhile, ultra-low frequencies (under 10Hz, say) can create pretty, pulsing tremolo effects. But you always need to be careful when you adjust them, as the volume can get very quickly out of control.

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DI (Direct Injection) boxes

Like an Amp Simulator these are not considered effects however they have significance to performing musicians (connecting to an in-house PA system or studio recording rig) so I'm giving them a mention.

A DI box converts the guitar/effects output to a mic-lead connection. Besides the obvious difference in the shape of the connector there is also a difference in the signal transmitted:

<technical>

  • The guitar output (jack-lead) is a hi-Z (or high-impedance) signal
  • The DI outputs a lo-Z (or low-impedance) signal

Firstly these are both 'mic-level' or 'instrument-level' inputs (they carry very quiet signals) but hi-Z signals are more prone to interference. The lo-Z signal consists of the instrument's mono signal (hot) and it's inverted waveform (cold), the cables are twisted around one another such that any interfering signal generated in one is negated by the other (much the same as the way a humbucking pickup works).
</technical>

The result of this noise-cancellation is that the signal deteriorates less over distance.

There are two types of DI, active and passive, which have their own advantages and disadvantages a comparison can be seen here.

The next stage of signal processing is the pre-amp.

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Freeze pedal

Sometimes also called a "granular synthesizer", this effect allows guitarists to infinitely sustain what they are currently playing on their guitars.

Simple versions of this pedal are the Electro Harmonix "Freeze" pedal and the "Freeze" effect on the Boss ME-80 multi-effects pedal. A more sophisticated version is the Electro Harmonix "SuperEgo" pedal which allows control of the attack and fade of the otherwise infinitely-sustaining signal.

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