An effects pedal (or a "Stomp Box") is an electronic effects unit housed in a small metal or plastic chassis used by musicians, usually electric guitar players, to modify their instrument sound. Musicians playing electronic keyboards, electromechanical organs, the electric bass, or electric violin also use effects pedals. These devices alter the sound quality or timbre of the input signal, adding effects such as distortion, fuzz, overdrive, chorus, reverberation, wah-wah, flanging, phaser or pitch shifting. The sound of a guitar or other instrument that is played without an effects pedal is described as "clean", "straight" or "dry."
They are called pedals because they sit on the floor and have large on/off switches on top that are activated using the foot. Some pedals, such as wah-wah or volume pedals, employ what is known as an expression pedal, which is manipulated while in operation by rocking a large foot-activated (treadle) potentiometer back and forth. The relative position of the expression pedal thus determines the extent to which the sound is altered.
Effects pedals permit the guitarist/bassist to activate and deactivate effects while playing an instrument. Larger rack-mounted effect units are generally more expensive and delicate, but they have superior sound quality, and are used in studio applications for recording. Pedals are intended mainly for use in live performances.
When a pedal is off or inactive, the signal coming in to the pedal is shunted onto a bypass, so that the "dry" or unaffected signal can go on to other effects down the chain, and thus any combination of effects on a chain can be created without having to reconnect boxes during a performance. "True Bypass" means the presence of an isolated wire passing straight through the effects pedal, as opposed to "buffered bypass," which uses active circuit elements to connect the input to the output. While these are 2 popular configurations, there are other bypass methods, such as input-only bypass which is semi-passive.
The instrument signal can be routed through the stomp boxes in any combination, but to shape and preserve the clarity of the basic distortion tone, it is most common to put wah and overdrive pedals at the start of the chain; pedals which alter the pitch or color of the tone in the middle; and boxes which modify the resonance, such as flanging, delay (echo) and reverb units at the end.
EQ, auto-wah, phaser, and vibe effects fit naturally at any position without introducing intermodulation distortion, while the emphatically time-based effects can sound unnatural and chaotic if placed early in the chain. Effects pedals can be used together with other effects units and a guitar amplifier's built-in effects. However, when too many effect pedals are used, unwanted noise and hum can be introduced into the sound. Some performers use a noise gate pedal to reduce the unwanted noise and hum.
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 is a pedalboard.
Some 2000s-era bass amplifiers also have onboard effects, such as a suboctave generator and overdrive/distortion. On some bass amplifiers, there is an equalizer which can be switched on and off with the switching pedal. As with electric guitar amplifiers, these bass amplifiers often come switching pedals to allow the player to turn the effects on and off at their will.
Many other musical instruments, among them the piano, pipe organ, drums, and harp, also make use of pedals to achieve tonal, dynamic, or other effects. The piano's mechanical sustain pedal is one well-known example. Pipe organs and electromechanical Hammond organs have one or more expression pedals and sometimes a crescendo pedal, which the organist can use to achieve dynamic (or "expressive") changes. Some large church and theater organs also have push-buttons for the feet, so that the player can activate different stops. These are neither considered nor called effects pedals. Pipe organs and Hammond organs also use another type of pedals on their bass pedal keyboard, which is a 20- to 32-note keyboard operated with the feet.
One major exception appears on modern electronic organs and synthesizers, which usually include a volume pedal similar to that of a guitar. The electronic organ pioneered this kind of pedal, not the guitar. Some advanced models also include an additional effects pedal that may be programmed to serve several of the functions described in the preceding section. The operation of each is similar to those on guitars; the organist places an entire foot on the pedal and, while playing, gently pumps up and down with heel and toe pressure to achieve the desired effects. Because the organist is usually seated and thus has better balance than the guitarist, the pedals are designed to have a wider range of motion. The organist can thus bring about more pronounced changes than the guitarist with only slight changes in foot pressure.
Some pedals, in fact also have switches on the end that enable still other effects by "scrunching" the toes to the left or right on the pedal, either in isolation or while pumping the pedal up and down, leading to far more flexibility than most guitar pedals.
Another stompbox found in solo music is the foot drum-style stompbox. The unit will commonly connect to a PA via an XLR or guitar jack and provide the Front of House speakers with a kick drum sound which can add rhythm to solo acoustic music. Some musicians use homemade stomp boxes which consist of a wooden box and a microphone.