MIDI, or Musical Instrument Digital Interface, is a protocol for sending digital information between electronic music instruments and equipment, including computers and signal processors (devices that modify sounds by adding reverberation, modifying pitch, and other means). The basic protocol addresses common functions, such as notes, timing, pitch, and pedal information. MIDI keyboards, guitars, violins, and drums have become as common as the synthesizer in electronic music. MIDI permits such instruments to be connected to one another and to computers, which are often used as sequencers (devices that control the output of musical instruments and signal processors).