An electric guitar is a guitar that uses one or more pickups to convert the vibration of its strings into electrical signals. The vibration occurs when a guitar player strums, plucks, fingerpicks, slaps or taps the strings. The pickup generally uses electromagnetic induction to create this signal, which being relatively weak is fed into a guitar amplifier before being sent to the speaker(s), which converts it into audible sound. The electric signal can be electronically altered to change the timbre of the sound. Often, the signal is modified using effects such as reverb, distortion and "overdrive"; the latter is considered to be a key element of electric blues guitar music and rock guitar playing. Invented in 1932, the electric guitar was adopted by jazz guitar players, who wanted to play single-note guitar solos in large big band ensembles. Early proponents of the electric guitar on record include Les Paul, Lonnie Johnson, Sister Rosetta Tharpe, T-Bone Walker, and Charlie Christian. During the 1950s and 1960s, the electric guitar became the most important instrument in popular music. It has evolved into an instrument that is capable of a multitude of sounds and styles in genres ranging from pop and rock to country music, blues and jazz. It served as a major component in the development of electric blues, rock and roll, rock music, heavy metal music and many other genres of music. Electric guitar design and construction varies greatly in the shape of the body and the configuration of the neck, bridge, and pickups. Guitars may have a fixed bridge or a spring-loaded hinged bridge, which lets players "bend" the pitch of notes or chords up or down, or perform vibrato effects. The sound of an electric guitar can be modified by new playing techniques such as string bending, tapping, and hammering-on, using audio feedback, or slide guitar playing. There are several types of electric guitar, including: the solid-body guitar; various types of hollow-body guitars; the six-string guitar (the most common type), which is usually tuned E, B, G, D, A, E, from highest to lowest strings; the seven-string guitar, which typically adds a low B string below the low E; the eight-string guitar, which typically adds a low E or F# string below the low B; and the twelve-string guitar, which has six pairs of strings. In pop and rock music, the electric guitar is often used in two roles: as a rhythm guitar, which plays the chord sequences or progressions, and riffs, and sets the beat (as part of a rhythm section); and as a lead guitar, which provides instrumental melody lines, melodic instrumental fill passages, and solos. In a small group, such as a power trio, one guitarist switches between both roles. In large rock and metal bands, there is often a rhythm guitarist and a lead guitarist.