rock band
Rock band (or rock group) is a generic name to describe a group of musicians specializing in a particular form of electronically amplified music. Deriving its name from the musical style which was its immediate progenitor, rock and roll, the type of music played by rock groups has its roots deeply steeped in both rock and roll, and its immediate forebear, rhythm and blues.
Instruments
A rock group tends to have a heavy focus on certain instruments, principally electric guitar, bass guitar, and drums. Keyboard instruments such as electronic organs were featured from the outset by groups such as Manfred Mann and The Animals, and later in the 1960s, rock bands such as The Who, Pink Floyd, The Doors and Hawkwind experimented with synthesizers. Practically any other musical instrument, however, may be deployed within the context of a rock band, for example the flute (Jethro Tull), violin (Kansas), pipe organ (Arcade Fire), bagpipes (AC/DC), or theremin (Pixies).
Structure
A rock group or band usually consists of at least four musical roles: lead singer, guitarist, bass guitarist, and drummer, forming a quartet (group of four) such as Queen. A band comprising only three members, often called a "Power Trio", with one of the instrumentalists singing as well, is also common. Examples include Rush, ZZ Top, The Jimi Hendrix Experience, Cream, Nirvana, The Police and Pompus Green.
Many rock bands also include a rhythm guitarist and/or a keyboardist, who work with the bassist and the drummer in the rhythm section. The role of these instruments is to identify and play chords and chordal accompaniment for the soloist and to merge with the overall groove of the rhythm section.
The lead singer may also play an instrument while singing, most commonly the guitar, bass guitar, or keyboard. When the lead singer role is taken by one of the other primary musicians, unusual configurations are possible, such as the three-guitar model of such bands as Molly Hatchet and Radiohead. One of two or more guitarists in a band may usually play either rhythm or lead exclusively, especially when performing live; however, when they are in the studio, they may switch roles.[citation needed]
Furthermore, some bands, especially in nu-metal and rapcore, may even have rappers and/or turntablists in the line-up, such as in the band Linkin Park.
If there is an addition of instruments from other areas of music, such as stringed instruments like a violin or cello, or horns like trumpets or trombones, the band is seen as diverging too far from the main four roles, creating a tendency to classify the group not as a rock band, but with a genre seen as more specific than "rock" (e.g. heavy metal or progressive rock).
While some rock bands may add several additional singers and instrumentalists, they hardly ever lose the four primary roles. Some notable exceptions are The White Stripes, Local H (who consist of only a drummer and a guitarist/singer), Ben Folds Five (who consist of only drums, bass, piano and vocals) and Keane (which consists of drums, keyboard and vocals).
The most common formation for rock/metal bands in recent times is a quintet consisting of vocalist, lead and rhythm guitarists, bassist, and drummer.