Extreme

Extreme music is a term used to describe a variety of musical styles including subgenres of extreme metal, hardcore punk, hardcore techno, industrial, noise, and also some free jazz.
Definition
Extreme music is categorized as music that contains one or more elements that are abhorrent to the average listener (in some cases leading to debates as to whether certain artists' work can even be described as music). These may include: unusual tempos (very fast or very slow), unusual quantities of harsh and abrasive sounds such as guitar distortion or white noise, excessive volume, highly obscene or violent lyrics (often in combination with an unusual vocal style, such as screams, barks, growls or heavy glitch distortion), dissonant or atonal scales and unusual, often jazz-based time signatures, very rapid and jarring changes of tempo or even genre, highly unusual song structures and lengths etc., often in combination with each other.
In most fans' definitions, any sort of overt popular exposure (i. e. regular radio-play on commercial channels, appearance on MTV) will negate a genre or style's status as extreme, as the term necessarily describes something that is beyond the scope of the current mainstream. An example of what was once deemed (or would have been deemed) extreme style that is no longer considered so is various traditional forms of heavy metal, as it is now a widely accepted form of music but was shunned when it first appeared. More modern forms of metal such as thrash metal and death metal are still considered extreme music, although both of the genres have some airplay and media exposure, especially the former.
'Common' extreme music styles
* Avant-garde: Although not all avant-garde artists fall under the 'extreme music' blanket, many do. Arnold Schönberg and Alban Berg often dealt with macabre subject matter in a dissonant style; atonality is often difficult for the listener. Works by Krzysztof Penderecki and Iannis Xenakis are also extremely demanding and abrasive to the ears. Polystylistic work by John Zorn and others sometimes borrows from other extreme music styles. The so-called New Complexity is a highly difficult brand of contemporary avant-garde composition.
* Avant-garde jazz: Some free jazz work by Ornette Coleman, Archie Shepp, and late work by John Coltrane is very intense, sometimes composed of two channels of distinct improvisation. Peter Brötzmann also performs in this style, directly exploring themes of war and conflict.
* Black metal: A sub-genre of extreme metal characterized by extreme tempo, high-pitched, screamed or growled vocals, violent and often satanic lyrics and corpse paint, a form of make-up that black metal bands wear to give the impression of that they are rotting corpses. The name of the genre is taken from the Venom album Black Metal.
* Breakcore: Breakcore is a loosely defined electronic music style which mixes together elements of jungle/drum & bass, hardcore techno, glitch and industrial.
* Death metal: Death metal is an extreme evolution of thrash metal. The vocals are low, indecipherable grunts and growls, but occasional high-pitch screams are not uncommon. The name of the genre is taken from pioneers Death, and the generally nihilistic and violent lyrics may also have inspired the name of the genre.
* Doom metal: Doom metal is a slow and heavy form of heavy metal, inspired by the slow, apocalyptic sound of Black Sabbath. Vocals can be clean, but usually they are in a grave, slow growling. Lyric themes are usually dark and depressing. In drone doom, the most extreme subgenre of doom metal, the extreme slowness of the music makes single songs reach over 20 minutes. Heavy metals characteristic guitar riffs are mostly absent, and if riffs exist these can last for over a minute. The doom subgenre sludge metal utilizes hardcore punk influences as well, and often involves lyrics about drug abuse.
* Extreme metal subgenres: Extreme metal covers multiple genres, such as black metal, death metal, thrash metal and doom metal. Many of these genres have had significant crossover with both heavy metal genres and hardcore punk genres, as well as evolved over the years, creating genres such as death/doom, groove metal, sludge metal, brutal death metal, melodic death metal, viking metal, dark metal, goregrind, crossover thrash, deathcore and many others.
*Gabber: sub-genre of hardcore techno, uses a very hard 4/4 beat, harder and faster than more commercial hardcore.
*Grindcore: Grindcore fuses crust punk with varying amounts of influence from crossover thrash, thrashcore and death metal to create an extremely fast and violent form of music. Lyrics are sometimes delivered in a style that is totally indecipherable, being little more than a series of grunts or squeals, that can only be understood with the aid of a lyrics sheet. Songs are often short, with tracks under a minute in length not uncommon. Napalm Death is often credited as its originator, but this distinction may fall to bands like Repulsion and DRI. Another well-known band to fall within this genre are the group Anal Cunt, the self-styled 'worst band in the world'.
*Hardcore punk: Although "normal" hardcore punk is not generally considered extreme music, there are many narrow sub-genres that can be considered extreme music. Common traits are shouted vocals, loud power chord driven guitars and aggressive lyrics.
*Industrial music: a name for a large number of sub-genres that use noise in a musical context, although some industrial is not considered extreme.
*Mathcore: A fusion of hardcore punk, extreme metal and avant-garde jazz. The genre is categorised by its aggressive style and screamed vocals coupled with highly technical jazz instrumentation which shifts tempo and time-signature in bizarre and often unexpected ways. Lyrics often make use of extended, overly subtle poetic allegories and surreal imagery that are often accused of being overly pretentious. This style has recently received much critical attention due to the relative popularity of The Dillinger Escape Plan.
*Noise music: related to experimental industrial music and drone, noise music is a mainly electronic form that rejects traditional musical elements (such harmony, melody and rhythm) and often looks at music as a series of events instead. With most of its focus on texture, it uses sounds that the average listener would think of as ‘uncomfortable’ and even ‘painful’. Some noise artists have received much praise from critics for their original and often subtle musical experimentation, but very few bands have any sort of widespread fanbase, with perhaps Merzbow being a minor exception. Noise music encompasses noise rock, noisecore (noise-induced techno and dance), and simply general noise used expressively.
*Noise rock: Rock groups, such as Big Black, The Jesus Lizard, the Boredoms, and Wolf Eyes, extend traditional punk rock into extremes of volume and sometimes compositional formlessness.
*Power noise: sub-genre of industrial music, uses harsh noise in rhythmic, maybe danceable context
*Power violence: Hardcore punk heavily influenced by grindcore. Pioneers of the genre include Neanderthal, Infest, Crossed Out, Spazz, and Man Is the Bastard.
*Speedcore: Speedcore is a subgenre of 1990s hardcore techno music which extols massively high bpm counts, normally taken to mean anything over 300 bpm (five beats per second). As with grindcore, tracks are often very short.
Seminal extreme artists
These are some bands which are commonly agreed to have had some significant effect on the molding or shaping of what we now call extreme music. Many of these bands have since been left behind by what would commonly be called 'extreme' music:
*Bathory: First three albums were crucial in the creation of the lo-fi, often very minimalist form of metal known as black metal. Later progressed to become key in the development of viking and folk metal.
*The Berzerker: The first band to attempt mixing extreme metal with speedcore.
*Carcass: Created the gore subgenre of grindcore known as goregrind. Directly inspired countless other groups, such as Cattle Decapitation, Exhumed, and The County Medical Examiners.
*Celtic Frost: Introduced the avant-garde to heavy metal.
*Death: Usually credited with being one of the first death metal bands.
*Earth: Generally considered to be the pioneers of drone metal.
*Knut: Widely forgotten, but highly influential in the formation of the genre known as mathcore.
*Merzbow: One of the most innovative and influential, and certainly best-known, noise musicians.
*Napalm Death: Progenitors of grindcore.
*Suffocation: One of the first bands to experiment with death metal to create more complex songs, pioneering the style known as brutal death metal.
*Swans: Part of the NY No Wave scene in the 80's, they used extremely slow tempos, violent lyrics, white noise, and played shows at such a loud volume that some members of the audience would vomit.
*Throbbing Gristle: Founders of Industrial Records and coined the term "industrial music".
*Venom: At the time of its release Black Metal was one of the most extreme records ever heard, and gave a name to a genre, as well as direction to the next twenty years of European extreme metal.
*Venetian Snares: Produces experimental IDM, breakcore and glitchcore in non-4/4 time signatures (mostly in 7/4).
*Whitehouse: Inventors of the extreme industrial/noise music genre "Power Electronics".