What is metal? 
Metal is a form of music originating in the UK and USA rock scenes in the very late 1960s. Arguably, the progenitors of the style were Black Sabbath, Deep Purple, and Judas Priest. It is known for powerful vocals, distorted and really loud electric guitars, deep bass lines, heavy beats and drums and the extensive use of 5th chords ("power chords") and a minor feel. The default time signature for metal is 4/4; however, a large number of metal acts display a higher level of musicianship than rock acts, and thus time signatures can vary widely to include compound and even asymmetric meters.
The general instruments in a metal band are electric guitars (acoustics are not used as widely), bass guitars, and drum kits. In some genres keyboards are common. Many of metal bands use guitar techniques such as sweeping and fretboard tapping (to play fast melody patterns, especially arpeggios), whammy bar diving (pushing down the vibrato bridge all the way to create a guttural roaring sound), and pinch harmonics (partially stopping a vibrating string with the picking hand to create a very high-pitched harmonic with a distinctive "squealing" tone).
Due to misunderstandings, there are some genres that are either fusions of metal with other genres, or not metal at all. For example, Visual Kei (a type of J-Rock) is often interpreted as metal, due to the heavy use of makeup (which is a typical practice of especially earlier metal acts) and some stylistic elements common to metal. Some other groups are a matter of constant genre debate, such as Slipknot.
General genres of metal 
Metal artists tend to divide and sub-divide their genres extensively. The sheer number of metal genres is expansive; see this Wikipedia article for an in-depth list.
Heavy metal 
Heavy metal is generally regarded as synonymous with the general term "metal". It is characterized by its "heavy" sound, that is, one with a crunchy, bass-heavy feel. The term "heavy metal" comes from the the novel "Naked Lunch" by William S. Burroughs but was popularized by the song "Born to Be Wild" by Steppenwolf which features the term in it's lyrics. Not many bands are labeled as simply heavy metal - it is more of a general term if anything. It started in 1969 when black Sabbath combined blues rock, psychedelic rock, and even a little influences of darker, louder classical music pieces, industrial sounds, and the fluent drumming and bass of jazz. The band also wanted to talk about horrible stuff that was going on back then, and create a more dark, atmospheric sound. This early form of metal used pentatonic style soloing, sludgy, jazz style tom-tom and cow bell drumming, and a minor scale rhythm section. In 1980, the new wave of British heavy metal came about, and added more hardcore punk influence, lots of the songs were in a minor key. early 80's NWOBHM music usually talked about riding motorcycles, had harmonies, and were very melodic.
Thrash metal 
Thrash metal (a faster style of thrash metal is known as speed metal) is a heavy metal derivative, played at high speed and aggression. It is characterized by use of pedal notes and speed-picking or strumming of these or power chords based on these roots. Thrash came when scene kids in the bay area wanted to feel big, and combined British hardcore punk rock and New Wave British heavy metal. Thrash metal originated from the Bay Area of California, with bands such as Metallica and Exodus, from L.A., Slayer & Megadeth, and from New York, Anthrax, pioneering the sound. Metallica, Megadeth, Anthrax and Slayer are often referred to as the "Big Four" of thrash metal. Other early bands include Exodus, Testament, Overkill, etc. Other honorable mentions include Kreator, Sodom and Destruction, who are sometimes referred to as "The Unholy Trinity" of German thrash metal. The thrash metal band Possessed is known to pioneer the death metal genre.
Examples of thrash metal classics are, Anthrax's Caught In A Mosh, Megadeth's Holy Wars, Metallica's Battery, and Slayer's Angel of Death. Many thrash bands like Destruction, Vio-lence, Kreator, Death Angel, Dark Angel, Megadeth, or Testament had a more technical side to their music. Testament's lead guitar work was influenced by jazz, destruction's and megadeth's by classical music. Most thrash songs use methods like palm muting, fast paced tremelo picking, fast double bass blast beats, minor scales, blues scales, or tapping. Thrash was mostly influenced by hardcore punk, and some thrash bands like DRI, suicidal tendencies, and municipal waste have added a little more punk influence and created crossover thrash. The riffs are very fast, solos a little short and simplistic, fast paced shouting, and most songs are in either e minor or d minor.
Doom metal 
Doom Metal, inspired mainly by Black Sabbath, has many offshoots with varying sounds. The "traditional" side include the bands Saint Vitus, Pentagram, and Trouble who differ little from the template set by Black Sabbath. Bands such as Sleep and Electric Wizard are considered the "Stoner" side that is expanding upon the ideas set forth by Black Sabbath and have a very heavy, slow, psychedelic tint. The other side of the spectrum includes "the Peaceville three" such as My Dying Bride, Paradise Lost, and Anathema, who play a more gothic, depressive style. Doom Metal consists of down-tuned guitars and has a slow, heavy sound with both picked and slap bass with hard rock drum beats, sometimes with two bass drums. The vocals consist of imaginations of the dark side of human beings or drugs. The vocal tone is cand either be trebled or growled, reaching high and deep vocal patterns quickly throughout the song. Doom metal bands like heaven and hell, sleep, trouble, electric wizard, black sabbath, witch finder, and acid witch usually play their songs in either the blues scale, pentatonic scale, e flat minor, c and c sharp minor, or f minor. The speed is usually somewhere around 60bpm
Power metal 
Power metal is one of the most melodic forms of metal. It originated in the United States and Europe, largely growing in two separate but related types: American or traditional power metal and European or melodic power metal. Both brands contain very high tempos and melodic harmonies. Clean vocalists are the most common within the sub-genre but power metal bands with backup or even lead harsh vocalists are not uncommon. Traditional power metal evolved as a direct successor of NWOBHM, traditional heavy metal and speed metal with a larger emphasis on aggression and speed than its European counterpart. Bands like Jag Panzer, Manowar, Virgin Steele and Omen are examples of traditional power metal. On the other hand, European power metal has a larger emphasis on an epic atmosphere, better production values and an often less aggressive style. The extensive use of keyboards, in order to accentuate the atmosphere or to produce a symphonic sound is also very common. Examples of melodic power metal bands include Rhapsody of Fire, Avantasia/Edguy, later Blind Guardian, Stratovarius, Sonata Arctica, Dragonforce, Lost Horizon, etc.
Death metal 
Death metal is noted as being an "extreme" subsidiary of thrash metal. Drums and down-tuned, distorted guitars playing fast, intricate, almost unintelligible rhythms, and "growled" vocals all contribute to the intense power of the style. The lyrical content usually deals with the darker, nihilistic side of human imagination, with subjects such as death, gore, and the occult. However, death metal is not limited to conventional dark subject matter. It can also range out to philosophy (like later-era Death), mythology (such as the band Nile), and politics.
Death metal is often distinguished by the American and European types. Melodic Death metal is known for its harmonies and unique groove melodies. Technical/melodic metal uses a lot of pinch harmonics.Even with these harmonies it still retains heavy aggression and intensity. This brand of death metal was made popular by bands like At The Gates, In Flames, Carcass, Eucharist, and Dark Tranquility. To some extent, the Finnish metal band Children of Bodom has many of the attributes of this genre.
Technical death metal is a complicated brand of the genre. These bands are just as aggressive as their other metal counterparts. They are distinguished by odd rhythms and melodies, as well as complex time signatures and complicated structuring. Bands of this genre include Suffocation, Decapitated and Atheist. Popular technical death metal band Necrophagist incorporates classical music into their playing.
Deathcore is a fusion of death metal and hardcore that is much harsher variation and an offshoot of Metalcore, often dealing with typical death metal gore topics. Their playing is often down-tuned and either incredibly fast or slow and jagged. It tends to focus very much on the "breakdown", and tends to use less melodic tendencies. Popular bands: Suicide Silence and Whitechapel. Deathcore, like Metalcore is usually debated whether or not, it is a legitimate metal genre.
Black metal 
Black metal is known for its cold atmosphere and its often pagan or satanic imagery. Early innovators of Black Metal included Hellhammer/Celtic Frost and Bathory, whose style was expanded upon by the Norwegian Black Metal scene, pioneered by such bands as Mayhem, Darkthrone, Emperor, and Burzum. Black metal's vocals are usually either performed as guttural rasps or as harsh shrieks. Melodies are typically heavily tremolo picked, such as the guitar work on Dissection's "Where Dead Angels Lie", or include power chords. Black metal bands tend to be divided into the more primitive, low-fi bands such as Darkthrone, and the more refined bands that use electronic synthesizers such as Emperor. Many of modern black metal songs are in the key of a minor. In black metal's early years (1982-1987), there were two ways to play black metal. The one way was to take punk rock riffs, combine them with the rasp vocals, and make the riffs darker, heavier, and faster. The other way was to take thrash, add deeper, darker vocals, sing satanic lyrics, and create a darker atmosphere.
Folk metal 
Folk metal made its way in a lot of the Scandinavian countries, mainly in Finland by Korpiklaani ("Forest Clan") and Finntroll, which has more of a polkish feel to them. The instruments consist of classic instruments such as fiddle, accordion, acoustic guitar, and mandolin. and mixed with new style of instruments such as guitar wailing and the drums and a fast beat sometimes substituted with congas. but the instruments play with the same way thrash metal does making it sound great with the vocals mostly having yellin European accent. Example: Skyforger, Eluveitie.
Gothic metal 
Gothic metal is characterized by darker modes and arpeggios such as aeolian, phrygian and locrian modes to contribute a heavy, bassy sound and a very somber, dark feel to the music.Modern bands also apply the usage of drum machines and Electric Keyboards. Strong classical influences are often evident in string arrangements and piano parts. An example of a Gothic metal act would be Lacuna Coil.
Symphonic metal 
As the name suggests, symphonic metal attempts to give a classical feel to metal, either by using a symphony orchestra in tandem with the standard instrumentation of metal, or by using electronic keyboards to simulate symphonic textures such as strings and brass. The Finnish band Nightwish is an example of this style.
Progressive Metal 
Progressive Metal is a genre of metal often linked to music of technical expertise. The term 'progressive' is widely debated as to what defines it. A common understanding is that progressive metal often changes tempo, time signature, key signature, and over all styles within one song. A few key examples of progressive metal are the bands Between The Buried and Me, Protest The Hero, Sikth, The Human Abstract, Dream Theater, Opeth, Nevermore, Symphony X, Ayreon and Pain of Salvation.
Industrial Metal 
Industrial metal fuses the cold, mechanical, electronic sound of industrial music with the amplified guitars of metal. It is not as simple as that, however, as there is a continuum of music ranging from merely industrial with distorted guitars to full-on heavy metal with synthetic-sounding drums and heavy electronics use. Industrial metal that veers toward the metallic side is often called "cyber metal", and the latter sub-genre includes such bands as Strapping Young Lad and Fear Factory. More "pure" industrial metal bands would include Godflesh, Ministry, and Samael's later outputs. As industrial music often has a political bent, so too does industrial metal, though perhaps a more militant one.
Glam Metal 
Generally, glam metal or hair metal has hedonistic lyrics, often focuses on sex, alcohol, and sometimes drugs(but not so simply as you mgiht think). Some many of the first wave bands had some songs related to the occult. Musically, glam metal songs often featured distorted guitar riffs, shred guitar solos, anthemic choruses, hard hitting drumming, and complementary bass. Glam metal is often frowned upon by fans of other genres of metal as being too pop influenced. Nevertheless, this can vary from band to band and it also depends largely on which time frame they played the style. Examples of glam metal bands are Mötley Crüe, Ratt, Lita Ford, Poison, Bon Jovi and Quiet Riot
Nu-metal combines typical metal sounds with heavy rap and/or hip-hop influences. A nu-metal group will sometimes include a turntablist or a musician who plays keyboards and samplers, helping to add the sounds that are common in hip-hop music. Hip-hop drum-and-bass grooves are common; as is rapping. Examples of nu-metal groups may or may not include KoRn, Linkin Park, Coal Chamber, Slipknot and Limp Bizkit; however, due to the bad reputation that the genre has, many artists debate that they are indeed not allied to the style. Moreover, it is usually shunned by many Metalheads and is arguable whether or not it is a legitimate Metal genre. Nu metal originated out of groove metal, alternative metal, rap, and industrial metal in 1994. Often funk metal and groove metal riffs are used and down-tuned guitars or tri-tones. But that wasn't always important. The music contains a mixture of grunge, metal and hip hop. But it's criticized by some people familiar with older metal.
Groove metal 
Groove metal started in 1990 with bands like Pantera and Exhorder and Sepultura, it featured down-tuned guitars, burly and strong, heavy, muscular-like beats, heavy and usually angry vocals, groovy-like but very aggressive riffs and groove-heavy like bass lines and strong drums with a pure power that heavy metal must have. Other bands considered groove metal include Five Finger Death Punch and Lamb of God.
Musical style 
The genre of metal is immensely varied. However, there are many common theoretical traits that appear in almost all metal music, regardless of sub-genre.
Most metal songs will express only one mood for the duration of the song; sometimes maybe two or three (often corresponding to "verse-bridge-chorus" structure). However, the more "progressive" metal acts (of which the numbers are steadily climbing) often write epic mood pieces that display an impressive evolution of musical moods, reflecting the lyrics, which often revolve around very complex emotional subjects.
The overall mood, whether it be "sad" or "angry", is most often very dark; indeed, for many people, metal is the quintessential "evil music".
Metal is a highly rhythmic style of music, even by modern standards. The drums are of cardinal importance; and often, the guitars will often repeat only one or two chords, emphasizing the strumming rhythm rather than the harmonies.
Simple metal usually sticks to 4/4 time signatures (and sometimes 6/8 or 3/4), although it may be played at very high speeds. A number of groups maintain the simple 4/4 beat in the drums while employing intricate syncopations around the beat. More technical groups make extensive use of compound metres, and even irregular time signatures such as 7/8 and 5/4; the rhythm is often further complicated by frequent time changes. The song Jambi by Tool is an excellent example of the complex rhythms sometimes exhibited in metal.
There are also songs with uneven metres such as Metallica's Master of Puppets where the main verse riff follows the pattern 4/4, 4/4, 4/4, 11/16 repeatedly.
Metal can sometimes be one of the most melodic styles of popular music; and conversely, it is often completely devoid of melody.
Sometimes, metal singers "growl" to the accompaniment of one- or two-chord progressions and a highly prominent, driving drum beat. The guitar(s) and bass play the rhythmic pattern ("riff") in unison; and the growl is non melodic. Since the music has no obvious melody, the listener's attention is drawn to the powerful rhythm. Short guitar melodies (often referred to as "licks") may be played in between vocal phrases, almost in imitation of the call-and-response style of jazz and blues.
However, it is also common for metal acts - especially in such genres as symphonic and "power" metal - to play "epic"-sounding chord progressions that can sometimes almost rival the complexity of Baroque-era art music. In such instances, either the vocalist or the lead guitarist may carry the melody; sometimes both do, in tandem. However, the music remains almost strictly homophonic.
Metal melodies are more often than not in minor keys. Very often, scales with a minor 2nd or (b2) are used to create a tense, dissonant feel. Because of this choice of scales - and also because of the similarity of the guitar to many folk instruments of the Middle East and upper Africa - a large number of metal acts incorporate strong influences from these folk styles in their music. Often, this takes the form of "Arabic"-sounding scales such as the Phrygian Dominant. The melody-dominated homophonic nature of metal assists this assimilation. Perhaps the most popular example of such music is System Of A Down - the members of this band are all Armenian-American, and make frequent use of Armenian and Turkish folk instruments and melodic patterns alongside their distorted guitar riffs.
The dynamics of metal is perhaps the stylistic aspect that differs most between its sub-genres. However, for the most part, the genre uses terraced dynamics - in an uncannily similar situation to that of Baroque art music, the main instrument of the genre (harpsichord for Baroque music, and distorted electric guitar for metal) is limited in its dynamic capabilities; and thus the whole band reverts to only a few different volume levels. This is not to say that these volume levels are limited in range, but merely that they are limited in number; a band may play at just a few different volumes, but these volumes can differ widely from each other. Many, if not most metal bands make dynamics a significant aspect of their music, often immediately following a quiet, subdued section with a very loud one, or vice versa.
The textures of heavy metal are distorted and thick. The instruments often play across all frequency ranges: the drummer plays the deep bass drum alongside high-pitched cymbals; the rhythm guitar and bass play low, guttural rhythms; and the lead guitar plays in the extreme high registers, making frequent use of pinch harmonics.
Metal can be said to be largely texture-based; often, the rhythm guitar will repeat the same riff over and over again, while other instruments appear and disappear to cause gradual shifts in the overall feel.
Typically, metal makes frequent use (perhaps even overuse) of parallel 5th chords - "power chords", consisting of the root note, the fifth of the chord, and the root note again one octave up. The power chord on a distorted electric guitar has immense power. Thus metal guitarists often tune their guitars so that the lowest three strings form a power chord (usually DAD); whereby they can play fast, heavy riffs using only one finger to stop all the strings in the necessary position for a power chord anywhere on the neck. Because the rhythm guitar often follows the melody, it can be said that much metal is harmonized in perfect fifths; however, the presence of the fifth is a feature of texture rather than harmony. As metal progresses some bands are still looking for a thicker sound with more punch. The adoption of 4th chord voicing is more commonplace these days than in the 1980's and 1990's. Though some thrash bands such as Slayer would use them occasionally for color, you can hear them quite frequently in death metal bands. Another interval used to create tension in metal is called the Tritone (an augmented 4th or diminished 5th). At one time the Catholic Church banned and restricted this interval, and it is called the "Devil's Interval". The first riff in Black Sabbath's self titled album outlines this interval. Often, lead passages and vocal lines are harmonized in thirds, frequently in the minor scale.
The minor seven is also an important interval in metal harmony. Hammer-on or pull-off riffs, up or down from the octave to the flat 7, are widely used. Since the flat 7 is a blue note, metal harmony shares core elements with the Blues. Metal's extensive use of the tritone reinforces the connection. The result can be an implied dominant 7 chord, a gateway to modulation.
The lyrics of heavy metal range from the sublime to the ridiculous; however, due to the genre's "dark" feel, the words more often than not concern themselves with violence, hatred, anger and sadness. The words and music are often composed well together, in that the music reflects the singer's feelings. Other genres of metal (such as power metal) are often based around epic fantasies, great battles, or the joy of life.
Metal instrumentation commonly consists of one or two distorted electric guitar, electric bass, drum kit, and vocals. With some more fantasy based bands keyboards and synthesizers have become very common. Also, many symphonic bands use an entire orchestra for many songs or even entire albums.
Guitars are sometimes tuned to lower than the usual E standard tuning, to provide a deeper, heavier sound. Some acts use guitars with additional lower strings, either to facilitate the playing of fast lead passages, or to allow playing even lower than is possible with a detuned six-string. Some even combine these techniques! Seven-string guitars tuned to drop A are not uncommon. Also, the use of large tube amplifiers with multiple big (usually 12") speakers, along with heavy distortion pedals, assists in creating the signature metal sound. The naturally darker-sounding "humbucker"-type pickups are preferred.
Basses are more often than not of the 5-string variety, to allow lower playing. These instruments are also often detuned. The bass, however, is not often distorted - perhaps this is to preserve the low end of the frequency spectrum (which is often lost when distorting a bass with a conventional guitar distortion pedal). To keep up with the fast guitars, metal bassists often play with a plectrum.
Drummers make use of big bass drums, big snares and big cymbals. Brushes and subtle snare work are eschewed in favor of playing fast and loud. The use of two bass drums, or two pedals beating the same bass drum, is commonplace - this helps to play the pounding bass drum rhythms that carry and move the music.
Musicians of Metal, are often known for their virtuoso playing and are often praised for their talent. They often blend metal with other genres, and even combining certain types of metal with other types. Speed is a common attribute for metal performers. However things like complexity and diversity also make metal musicians stand out.
A major element of some heavy metal and other similar genres, such as grindcore or hardcore punk, that makes them different from other types of rock is screaming. Lots of times, in metal, instead of only singing, a vocalist may scream. Because heavy metal's mood is darker than other genres of music, screaming complements the music well. It is demanding, yet guttural. This means it differs from the way you or I scream when we're frightened or startled.
There are different types of screaming in metal:
- Growl: Growling often sounds beast-like and almost indiscernible. This most often exists in death metal music.
- Pig squeal: Pig squealing is also used primarily in deathcore and sounds very breathy and high pitched, close to a pig squeal.
- "Grim" scream: The high pitched, wailing growl used in black metal music. Can give the impression of a banshee or a howling wolf.
- Hardcore screaming: Hardcore punk influenced screamed vocals, which focus more on "standard" screaming rather than the advanced techniques of growling. Common in punk/metal crossover.
- Shouted vocals: Cleaner vocals but with an aggressive edge to it, aggression can vary from just slight to all out shouted vocals. Common in thrash metal music.