An electric guitar is a fretted stringed instrument with a neck and body that uses a pickup to convert the vibration of its strings into electrical signals. The vibration occurs when a guitarist strums, plucks or fingerpicks the strings. It is sensed by a pickup, most commonly by a magnetic pickup that uses the principle of direct electromagnetic induction. The signal generated by an electric guitar is too weak to drive a loudspeaker, so it is plugged into a guitar amplifier before being sent to a loudspeaker, which makes a sound loud enough to hear. The output of an electric guitar is an electric signal, and the signal can easily be altered by electronic circuits to add "color" to the sound or change the sound. Often the signal is modified using effects such as reverb and distortion and "overdrive", with the growling sound of the latter being a key element of the sound of the electric guitar as it is used in blues and rock music.