Thrash metal is a sub-genre of heavy metal music characterized by its fast tempo and overall aggression. The songs usually use fast percussive beats and low-register guitar riffs, overlaid with shredding-style lead work. The lyrics often deal with social issues and reproach for The Establishment, using direct and denunciatory language, an approach which partially overlaps with the hardcore genre.
The genre evolved in the early 1980s from combining the drum beats of hardcore punk with the guitar style of the New Wave of British Heavy Metal. It emerged partially as a reaction to the more conventional and widely acceptable glam metal, a less aggressive, pop music-infused heavy metal subgenre which appeared simultaneously. Thrash metal was an inspiration for subsequent extreme genres such as death metal and black metal.
Thrash metal generally features fast tempos, low-register, complex guitar riffs, high-register guitar solos and double bass drumming.The genre evolved in the early 1980s from combining the drum beats of hardcore punk with the guitar style of the New Wave of British Heavy Metal. It emerged partially as a reaction to the more conventional and widely acceptable glam metal, a less aggressive, pop music-infused heavy metal subgenre which appeared simultaneously. The rhythm guitar parts are often palm-muted and played with heavy distortion to create a tighter and more precise sound. Vocally, thrash metal can employ anything from melodic singing to shouted vocals. Most guitar solos are played at high speed, as they are usually characterized by shredding, and use techniques such as sweep picking, legato phrasing, alternate picking, tremolo picking, string skipping, and two-hand tapping.
The guitar riffs often use chromatic scales and emphasize the tritone and diminished intervals, instead of using conventional single scale based riffing. For example, the intro riff of Metallica's "Master of Puppets" (the title track of the namesake album) is a chromatic descent, followed by a chromatic ascent based on the tritone.
Speed, pacing and time-changes also define thrash metal. Thrash tends to have an accelerating feel which may be due in large part to its aggressive drumming style. For example, drummers often use two bass drums, or a double-bass pedal, in order to create a relentless, driving beat. Cymbal stops/chokes are often used to transition from one riff to another or to precede an acceleration in tempo. Some common characteristics of the genre are fast guitar riffs with aggressive picking styles and fast guitar solos, and extensive use of two bass drums as opposed to the conventional use of only one, typical of most rock music.
To keep up with the other instruments, many bassists use a plectrum. However, some prominent thrash metal bassists have used their fingers, such as Frank Bello, Greg Christian, Steve DiGiorgio, Robert Trujillo and Cliff Burton. Several bassists use a distorted bass tone, an approach popularized by Burton and Motörhead's Lemmy. Lyrical themes in thrash metal include warfare, corruption, injustice, murder, suicide, isolation, alienation, addiction, and other maladies that afflict the individual and society. In addition, politics, particularly pessimism and dissatisfaction towards politics, are common themes among thrash metal bands. Humor and irony can occasionally be found (Anthrax for example), but they are limited, and are exception rather than a rule.