Heavy metal (often referred to simply as metal) is a genre of rock music that developed in between 1968 and 1974 , largely in the United Kingdom and the United States. With roots in blues-rock and psychedelic rock, the bands that created heavy metal developed a thick, massive sound, characterized by highly amplified distortion, extended guitar solos, emphatic beats, and overall loudness. Heavy metal lyrics and performance styles are generally associated with masculinity and machismo.
The first heavy metal bands such as Led Zeppelin, Black Sabbath and Deep Purple attracted large audiences, though they were often critically reviled, a status common throughout the history of the genre. In the mid-1970s Judas Priest helped spur the genre's evolution by discarding much of its blues influence; Motörhead introduced a punk rock sensibility and an increasing emphasis on speed. Bands in the New Wave of British Heavy Metal such as Iron Maiden followed in a similar vein. Before the end of the decade, heavy metal had attracted a worldwide following of fans known as "metalheads" or "headbangers".
In the 1980s, glam metal became a major commercial force with bands like Mötley Crüe and Ratt. Underground scenes produced an array of more extreme, aggressive styles: thrash metal broke into the mainstream with bands such as Metallica and Megadeth, while other styles like death metal and black metal remain subcultural phenomena. Since the mid-1990s, popular styles such as nu metal, which often incorporates elements of grunge and rapping; and metalcore, which blends extreme metal with hardcore, have further expanded the definition of the genre.
Heavy metal is traditionally characterized by loud distorted guitars, emphatic rhythms, dense bass-and-drum sound, and vigorous vocals. Metal subgenres variously emphasize, alter, or omit one or more of these attributes. New York Times critic Jon Pareles writes, "In the taxonomy of popular music, heavy metal is a major subspecies of hard-rock—the breed with less syncopation, less blues, more showmanship and more brute force." The typical band lineup includes a drummer, a bassist, a rhythm guitarist, a lead guitarist, and a singer, who may or may not be an instrumentalist. Keyboard instruments are sometimes used to enhance the fullness of the sound.
The electric guitar and the sonic power that it projects through amplification has historically been the key element in heavy metal. The lead role of the guitar in heavy metal often collides with the traditional "frontman" or bandleader role of the vocalist, creating a musical tension as the two "contend for dominance" in a spirit of "affectionate rivalry". Heavy metal "demands the subordination of the voice" to the overall sound of the band. Reflecting metal's roots in the 1960s counterculture, an "explicit display of emotion" is required from the vocals as a sign of authenticity. Critic Simon Frith claims that the metal singer's "tone of voice" is more important than the lyrics. Metal vocals vary widely in style, from the multioctave, theatrical approach of Judas Priest's Rob Halford and Iron Maiden's Bruce Dickinson, to the gruff style of Motörhead's Lemmy and Metallica's James Hetfield, to the growling of many death metal performers, and to the harsh screams of black metal.
The prominent role of the bass is also key to the metal sound, and the interplay of bass and guitar is a central element. The bass guitar provides the low-end sound crucial to making the music "heavy". Metal basslines vary widely in complexity, from holding down a low pedal point as a foundation to doubling complex riffs and licks along with the lead and/or rhythm guitars. Some bands feature the bass as a lead instrument, an approach popularized by Metallica's Cliff Burton in the early 1980s.
The essence of metal drumming is creating a loud, constant beat for the band using the "trifecta of speed, power, and precision". Metal drumming "requires an exceptional amount of endurance", and drummers have to develop "considerable speed, coordination, and dexterity...to play the intricate patterns" used in metal. A characteristic metal drumming technique is the cymbal choke, which consists of striking a cymbal and then immediately silencing it by grabbing it with the other hand (or, in some cases, the same striking hand), producing a burst of sound. The metal drum setup is generally much larger than those employed in other forms of rock music.
In live performance, loudness—an "onslaught of sound," in sociologist Deena Weinstein's description—is considered vital. In his book Metalheads, psychologist Jeffrey Arnett refers to heavy metal concerts as "the sensory equivalent of war." Following the lead set by Jimi Hendrix, Cream and The Who, early heavy metal acts such as Blue Cheer set new benchmarks for volume. As Blue Cheer's Dick Peterson put it, "All we knew was we wanted more power." A 1977 review of a Motörhead concert noted how "excessive volume in particular figured into the band’s impact." Weinstein makes the case that in the same way that melody is the main element of pop and rhythm is the main focus of house music, powerful sound, timbre, and volume are the key elements of metal. She argues that the loudness is designed to "sweep the listener into the sound" and to provide a "shot of youthful vitality."
The rhythm in metal songs is emphatic, with deliberate stresses. Weinstein observes that the wide array of sonic effects available to metal drummers enables the "rhythmic pattern to take on a complexity within its elemental drive and insistency." In many heavy metal songs, the main groove is characterized by short, two-note or three-note rhythmic figures—generally made up of 8th or 16th notes. These rhythmic figures are usually performed with a staccato attack created by using a palm-muted technique on the rhythm guitar.
Brief, abrupt, and detached rhythmic cells are joined into rhythmic phrases with a distinctive, often jerky texture. These phrases are used to create rhythmic accompaniment and melodic figures called riffs, which help to establish thematic hooks. Heavy metal songs also use longer rhythmic figures such as whole note- or dotted quarter note-length chords in slow-tempo power ballads. The tempos in early heavy metal music tended to be "slow, even ponderous." By the late 1970s, however, metal bands were employing a wide variety of tempos. In the 2000s, metal tempos range from slow ballad tempos (quarter note = 60 beats per minute) to extremely fast blast beat tempos (quarter note = 350 beats per minute).
One of the signatures of the genre is the guitar power chord. In technical terms, the power chord is relatively simple: it involves just one main interval, generally the perfect fifth, though an octave may be added as a doubling of the root. Although the perfect fifth interval is the most common basis for the power chord, power chords are also based on different intervals such as the minor third, major third, perfect fourth, diminished fifth, or minor sixth. Most power chords are also played with a consistent finger arrangement that can be slid easily up and down the fretboard.