Effects pedals are electronic devices used by musicians, primarily electric guitar players, to alter the sound quality or timbre of electric or electronic instruments, and less often vocals picked up through microphones. They are called "pedals" because these devices usually take the form of small boxes that sit on the floor, are connected to the instrument and amplifier by long cables, and are turned on and off by tapping a pushbutton switch with one's foot. Some devices, such as wah-wah pedals, are also manipulated while in operation by rocking a foot pedal back and forth.

Some basic types of effects pedals are:

• Distortion - The familiar "rock guitar" sound. A distortion pedal takes a normal electric guitar signal and either amplifies it greatly or clips the peaks of the sound's waveform to impart a gritty, dirty, and/or harsh tone. Different types of distortion, each with distinct sonic characteristics, include regular distortion, overdrive or tube-style distortion, and "fuzz". Although most distortion devices use solid state circuitry, some "tube distortion" pedals are designed with actual vacuum tubes.

• Delay - Creates a copy of an incoming sound and slightly time-delays it, creating either a "slap" (single repetition) or an echo (multiple repetitions) effect. Delay pedals may use either analog or digital technology. Analog delays often are less flexible and not as "perfect" sounding as digital delays, but some guitarists prefer them; some early delay devices actually used magnetic tape to produce the time delay effect.

• Chorus/flanger - A variation on delay which includes a cycling, variable delay time, and the delay time is so short that individual repetitions are not heard. The result is a thick, "swirling" sound that may suggest multiple instruments playing in unison (chorus) or a simulation of the fluid "tape flanging" effect associated with the psychedelic rock music of the 1960s. The chorus effect was especially popular with guitarists in the 1980s.

• Phase shifter - This device 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 is a kind of hollow "whooshing" sound reminiscent of a flying jet airplane. 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.

• Wah-wah - This foot-operated pedal is technically a kind of band-pass filter, which allows only a small portion of the incoming signal's frequencies to pass. Rocking the pedal back and forth alternately allows lower and higher frequencies to pass through, the effect being similar to a person saying "wow". The wah-wah pedal, used with guitar, is most associated with 1960s psychedelic rock and 1970s disco.

• Volume pedal - Another rocking foot-pedal device, this is simply an ordinary volume control designed to be foot-operated while playing. A volume pedal enables a musician to fade into and out of a musical passage, or even individual notes. A guitar played this way sounds radically different because the percussive plucking of the strings can be softened or eliminated entirely, imparting an almost human-vocal sound. Volume pedals are also widely used with pedal steel guitars, as in country music.

• Compressor - This device does not radically alter the tone of an instrument the way the previously mentioned pedals do, but many guitarists use it as a kind of effect. A compressor acts as an automatic volume control, progressively decreasing the output level as the incoming signal gets louder, and vice versa. This evens out the overall volume of an instrument, and can make a guitar appear to sustain much longer than natural.