Many musical instruments generate an electronic signal as an output to an amplifier or recording device. Examples of such electronic musical instruments include electric guitars, microphones, and synthesizers. The output of such instruments can be readily modified using a device called an effect, which comprises: a means to input the audio signal; specialized audio circuitry to modify or enhance the signal; and a means to output the signal. Examples of effects include reverberation effects to make an instrument sound like it is being played in a large space like a concert hall or cathedral; equalization effects to change the tone of the instrument; and gain effects to boost the amplitude of electric guitar signal in specific ways prior to further amplification.
The input to an effect is an audio signal, which is most typically analog signal (although digital signals can be used) whose voltage varies over time. The output of an effect is also an audio signal, which is most typically an analog signal (although digital signals may be used with special speakers) whose voltage varies over time. In this manner, multiple effects can be used in series for a more complex signal modification.
The internal processing of an effect can typically be adjusted by the user, to some extent, with one or more controls provided in the form of switches, potentiometers, and input devices. Examples of such controls include: a switch to bypass the effect or engage it in the signal path; potentiometers to control intensity or rate; and a jack to accept a variable-voltage device to control some musical expression of sound.