A power Attenuator enables a player to obtain power-tube distortion independently of listening volume.  Examples of power attenuators are the Marshall PowerBrake, THD HotPlate and Weber MASS.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.

A Power-Tube pedal contains a power tube and optional dummy load, or a preamp 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.

Hi-Gain is the sound most used in Heavy metal. High gain in normal electric guitar playing simply references a thick sound produced by heavily overdriven amplifier tubes, a distortion pedal, or some combination of both–the essential component is the typically loud, thick, harmonically rich, and sustaining quality of the tone. However, the Hi-Gain sound of modern pedals is somewhat distinct from, although descended from, this sound.  Many extreme distortions are either hi-gain or the descendents of such. The Mesa Boogie Triple Rectifier Series of amps are an example.The distortion often produces sounds not possible any other way.

Fuzz was originally intended to recreate the classic 1960’s tone of an overdriven tube amp combined with torn speaker cones. Since the original designs, more extreme fuzz pedals have been designed and produced, incorporating octave-up effects, oscillation, gating, and greater amounts of distortion.Oldschool guitar players would use a screwdriver to poke several holes through the paperboard part of the guitar amp speaker to achieve a similar sound.

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.Used in conjunction with an amplifier, especially a tube amplifier, driven to the point of mild tonal breakup short of what would be generally considered distortion or overdrive, or along with another, stronger overdrive or distortion pedal, these can produce extremely thick distortion sounds much like those used by Carlos Santana or Eddie Van Halen. 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.  Today there is a huge variety of overdrive pedals.

Overdrive distortion is a well-known distortion. While the general purpose is to emulate classic “warm-tube” sounds, distortion pedals such as the ones in this list can be distinguished from overdrive pedals in that the intent is to provide players with instant access to the sound of a high-gain Marshall amplifier such as the JCM800 pushed past the point of tonal breakup and into the range of tonal distortion known to electric guitarists as “saturated gain.” Although most distortion devices use solid-state circuitry, some “tube distortion” pedals are designed with preamplifier vacuum tubes. Some guitarists will use these pedals along with an already distorted amp or along with a milder overdrive effect to produce radically high-gain sounds. In some cases, tube distortion pedals use power tubes or a preamp tube used as a power tube driving a built-in “dummy load.” Pedals designed specifically for bass guitar are also available.

Guitar effects are electronic devices that modify the tone, pitch, or sound of an electric guitar, or condition or reroute the signal in some fashion. Effects can be housed in small effects pedals, guitar amplifiers, guitar amplifier simulation software, and in rackmount 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.Electric bass players use bass effects, which are designed to work with low-frequency tones of the bass.

The overdriven sound of distortion, which alters a signal’s waveform by “clipping” the signal, is an important part of an electric guitar’s sound in many genres, particularly for rock, hard rock, and metal. Filtering-related effects such as equalizers are used to adjust the frequency response in a number of different frequency bands, either for subtle sound shaping, to notch out unwanted resonance, or to enhance certain frequencies. Some filtering effects are used for creating more pronounced effects such as the “crying” sound of the wah pedal, the funky tone of the auto-wah, or the vocal-like sounds of the “Talk box. Volume-related effects such as volume pedals are used to adjust the volume of an instrument, make notes or chords fade in and out, or create a tremolo effect by rapidly increasing and decreasing the volume. A more complex volume-related effect is the compressor, which acts as an automatic volume control and smoothes out the peaks and valleys in the signal.

Time-based effects such as delay or echo pedals create a copy of an incoming sound which can be used for reverb effects; very long delay times can be used as a looping pedal. Modulation-related effects include the swirling sound of rotary speakers such as the Leslie speaker, the “whooshing” sound of the electronic Phase shifter, the psychedelic rock-style flanger, or the shimmering sound of a chorus effect. Pitch-related effects includes octave effects and pitch shifting pedals which can be used with an expression pedal to give a smooth bend-like effect or to add a parallel harmony part to a melody. Other pedals include switcher pedals; noise gates; and multi-effect pedals, which contain many different effects in a single chassis.

Feedbacker/Sustainer
While audio feedback in general is undesirable due to the high frequency overtone, when controlled properly, it can provide true sustain of the sound (instead of using a distortion/compressor to make quiet notes louder, or a feedback of a signal in a circuit as in a delay unit). Several approaches have been used to produce Guitar feedback effects, which sustain the sound from the Guitar. The most primitive form, as used by Jimi Hendrix, is to use the feedback created when the Guitar is played in front of an instrument amplifier’s loudspeaker when it is set to a high volume.

The neck pickup can be used as a driver to push the strings based on the bridge pickup, such as the Sustainiac Sustainer and Fernandes Sustainer. A signal amplifier can be used to powers headstock transducer, which in turn sends feedback vibration down the string, as in Sustainiac’s Model C. A handheld string driver can contain a pickup and driver, as in the EBow, which uses a small electromagnet to vibrate the string, creating a bow-like sustained sound. A dedicated high-gain Guitar amp can be used in the control room, without a microphone, as a footswitch-controlled string feedback driver. The microphone is placed on the speaker cabinet of the main Guitar amp in the isolation booth or live room.

Switcher/Mixer (or “A/B” pedal)
A switcher pedal (also called an “A/B” pedal) enables players to run two effects or two effects chains in parallel, or switch between two effects with a single press of the pedal. Some switcher pedals also incorporate a simple mixer, which allows mixing the dry Guitar signal to be mixed with an effected signal. This is useful to make overly processed effects more mild and natural sounding. One example of the way this mixer can be used is to mix a “wah-wah” pedal can be mixed with dry Guitar to make it more mild and full-bandwidth, with less volume swing, or a strong phaser effect can be mixed with dry Guitar sound to make the phaser effect more subtle and musical. . Alternatively, a compressor can be mixed with dry Guitar to preserve the natural attack of the dry signal as well as the sustain of the compressor. For metal or hard rock Guitar sounds, the mixer can be used to blend a “warm” overdrive pedal and a metallic hard-edged distortion pedal.

Examples include:

Dunlop A/B pedal
Loop Master
Boss LS-2 Line Selector (also contains a mixer)

Noise Gate
Main article: Noise gate
A noise gate allows a signal to pass through only when the signal’s intensity is above a set threshold, which opens the gate. If the signal falls below the threshold, the gate closes, and no signal is allowed to pass. A noise gate can be used to control noise. When the level of the ’signal’ is above the level of the ‘noise’, the threshold is set above the level of the ‘noise’ so that the gate is closed when there is no ’signal’. While some people think that a noise gate is some type of filter that removes noise from the signal, this is not the case. When the gate is open, both the signal and the noise will pass through. However, when a chord or note is being played, listeners do not tend to notice hum or noise that is present, even though this hum might be quite distracting during a pause or rest in the music.

Noise gates are also used as an effect to modify the envelope of signals, removing gradual attacks and decays. For example, if a noise gate is used with a very resonant instrument such as a hollow-bodied Guitar, which normally has a long, sustained sound, the sound of the notes and chords can be substantially shortened.

Examples include:

Boss NS-2 Noise Suppressor
MXR M-135 Smart Gate

Multi-Effects Pedals
A multi-FX pedal is a single effects device that can perform several Guitar effects simultaneously. Such devices generally use digital processing to simulate many of the above-mentioned effects without the need to carry several single-purpose units. In addition to the classic effects, most have amplifier/speaker simulations not found in analog units. This allows a Guitarist to play directly into a recording device while simulating an amplifier and speaker of his choice.

A typical digital multi-effects pedal is programmed, with several memory locations available to save custom user settings. Many lack the front-panel knobs of analog devices, using buttons instead to program various effect parameters. Multi-effects devices continue to evolve, some gaining MIDI or USB interfaces to aid in programming. Examples include:

Tech 21 Sans Amp - A line of simulated analog effects with distortion and speaker simulation capability.
Line 6 POD range
Behringer V-Amp Pro
DigiTech RP series
DigiTech GNX series
BOSS ME-20, ME-50, GT-6, GT-8, GT-10
Zoom G2 series
Vox Tonelab series
Roland VG series
Korg AX series

Other pedals, effects, and accessories
Miscellaneous pedals and effects include power supply pedals, which can power a number of effects pedals and electronic tuner pedals. Guitarists who use a number of Guitar effects pedals may transport the pedals in a Guitar pedalboard, which is a flat board or panel which serves as a container, patch bay and power supply for effects pedals for the electric Guitar. Some pedalboards contain their own transformer and power cables, in order to power up to 12 (or more) different pedals. Pedalboards assist the player in managing multiple pedals. The entire pedalboard can be packed up and transported to the next location without the need for disassembly.

Pedalboards often have a cover which protects the effects pedals during transportation. There are many varieties of pedalboard cases, including homemade DIY pedalboard cases, store-bought pedalboard cases, and, for professional musicians, custom-made pedalboard cases. Hard shell pedalboard-cases have foam padding, reinforced corners, and locking latches which protect the pedals during transport; during onstage performance, with the lid removed, the bottom of the case serves as the pedalboard. Most pedalboards have a flat surface where pedals and their power supplies are attached using Velcro or other techniques, and they often have a removable lid or padding to protect the pedals when they are not being used. Some pedalboards have handles or wheels to facilitate transportation.

Octaver
Main article: Octave effect
An octaver mixes the input signal with a synthesised signal whose musical pitch is an octave lower or higher than the original. Effects that synthesize intervals besides octaves are referred to as harmonizers or pitch shifters, shown below. Octave up pedals are often used by lead Guitarists to add additional edge and clarity to their solo sound. Octave down pedals are used by Guitarists in bands without a bassist who want to add a lower-end sound, or by bassists who want an extended low range without having to buy a 5-string or 6-string bass.

Octave up pedals include:

Ampeg Scrambler
Electro Harmonix POG (Polyphonic Octave Generator)
Electro Harmonix HOG (Harmonic Octave Generator)
Octave down pedals include:

Boss OC-3 Super Octave
Electro-Harmonix Octave Multiplexer
MXR M-103 Blue Box

Pitch Shifter
Main article: Pitch shifting
A pitch shifter is a device that alters the pitch of the instruments. They are generally used with an expression pedal to give a smooth bend-like effect. Pitch shifters can also be used to electronically “detune” the instrument. Some examples are:

Digitech Whammy
Boss PS-5 Super Shifter
Electro Harmonix Harmonic Octave Generator

Rotary Speaker
Rotary speaker effects are created by accomplished by amplifying a sound through spinning speakers or horns and/or by placing a rotating baffle in front of a speaker. This creates a doppler effect, and depend on the speed of the rotation, translates into phasing, flanging, chorus, vibrato, or even tremolo. In addition to the basic rotating speaker sound, other effects created with these cabinets included changing the speed, turning the motor on and off (causing a pitch “wobble” effect), and using two rotating speakers at once, a rich, chorusing sound nicknamed the “voice of God” by Leslie fans.

Leslie speakers: The wooden cabinet has rotating baffle near the bass speaker, and a horn speaker that rotates like a siren. Originally designed for Hammond organs, they are also used by some Guitarists. Some Leslie enthusiasts claim that that no electronic effects or software modelling devices can duplicate the complex doppler effects that the speaker creates.
Fender Vibratone: This is a simplified version of Leslie Speaker, containing only a 10″ speaker with a rotating baffle.

Rotary Speaker Simulator
Electronic Leslie-style effects duplicate the sound of a rotating speaker, but they offer different simulations of the effects of the rotation speed, volume, and pitch modulation. Some Leslie-style pedals can provide two or more modulation effects at the same time. Despite the numerous different analog devices, it is very rare for them to be able to duplicate all aspect of a Leslie speaker. Thus, Rotary Speaker Simulator are always going to be digital, utilizing modelling algorithms to model the relations between the rotating horns and bass baffle, and how the sound bounce around the cabinet. As Leslie also have a tube amplifier, most of these pedals have an overdrive circuit. Some of these pedals can even accept an 11-pin Hammond organ keyboard input.

Boss RT-20 Rotary Ensemble Pedal: This is one of the few pedals that is capable of modelling all aspect of a Lesile Speaker.
Line 6 Rotomachine: Also a modelling pedal, it is available in a compact pedal size.
DLS Roto-Sim: Hybrid of analog with DSP modelling.

Vibrato
A Vibe or vibrato pedal reproduces the sound of a rotating speaker by synchronizing volume oscillation, frequency-specific volume oscillation, vibrato (pitch wavering), phase shifting, and chorusing in relation to a non-rotating speaker. The modulation speed can be ramped up or down, with separate speeds for the bass and treble frequencies, to simulate the sound of a rotating bass speaker and a rotating horn. This effect is simultaneously a volume-oriented effect, an equalization-oriented effect, and a time-based effect. Furthermore, this effect is typically related to chorus. Some vibe pedals also include an overdrive effect, which allows the performer to add “tube”-style distortion. Some Vibe pedals include:

BBE Soul Vibe
Voodoo Lab Microvibe
Some vibe-chorus pedals include

Dunlop Univibe
Dunlop Rotovibe
BBE Mind Bender
Phase Shifter
Main article: Phase shifter
A phase shifter creates a complex frequency response containing many regularly-spaced “notches” in an incoming signal by combining it with a copy of itself out of phase, and shifting the phase relationship cyclically. The phasing effect creates a “whooshing” sound that is reminiscent of the sound of a flying jet. This effect dominates the sound in the song Star Guitar by Chemical Brothers. The song was not played with any Guitars but one can hear the phasing effect. The instrument being phased was actually a synthesizer. Some electronic “rotating speaker simulators” are actually phase shifters. Phase shifters were popular in the 1970s, particularly used with electric piano and funk bass Guitar. The number of stages in a phase shifter is the number of moving dips in the frequency response curve. From a sonic perspective, this effect is equalization-oriented. However, it may be derived through moderate time-based processing. Some phaser pedals include:

MXR M-101 Phase 90
Boss PH-3 Phase Shifter
Electro-Harmonix Small Stone
Moog MF-103 12 Stage Phaser
DigiTech Hyper Phase

Flanger
Main article: Flanging
A flanger simulates the sound effect originally created by momentarily slowing the tape during recording by holding something against the flange, or edge of the tape reel, and then allowing it to speed up again. This effect was used to simulate passing into “warp speed,” in scifi films, and also in psychedelic rock music of the 1960s. Flanging has a sound similar to an auto-wah, but weaker, yet is closely related to the production of chorus.

The first pedal-operated flanger designed for use as a Guitar effect was designed by Jim Gamble of Tycobrahe Sound Company in Hermosa Beach, CA, during the mid 1970s. Last made in 1977, the existing “Pedalflangers” appear occasionally on eBay and sell for several hundred dollars. A modern “clone” of the Tycobrahe Pedalflanger is sold by Chicago Iron.Famous users of this Flanger effect include Randy Rhoads and Eddie Van Halen, coincidentally they both used the MXR M-117R flanger and Eddie Van Halen even has his own signature model now.

Examples:

Boss BF-3 Stereo Flanger
Line 6 Liqua Flange
MXR M-117R Flanger
Danelectro FAB Flange
Electro Harmonix Deluxe Electric Mistress
DigiTech Turbo Flange

Chorus
An electronic chorus effect splits a Guitar signal in two, modulating the second signal’s pitch and mixing back in with the “dry” original signal. The effect sounds like several Guitarists playing the same thing at the same time, resulting in a wide, shimmering or swelling sound. Some common chorus pedals are:

Boss CH-1 Super Chorus
Electro-Harmonix Small Clone
Ibanez CF-7 Chorus/Flanger
Line 6 Space Chorus
MXR M-134 Stereo Chorus
Detune effect on Digitech Whammy
TC Electronic Stereo Chorus /Flanger /Pitch Modulator