This section needs expansion
. You can help by adding to it. (August 2008)
The electric guitar, bass guitar and drum kit are the most common instruments used to play doom metal (although keyboards are sometimes used), but its structures are rooted in the same scales as in blues. Guitarists and bassists often downtune their instruments to very low notes and make use of large amounts of distortion, thus producing a very "thick" or "heavy" guitar tone, which is one of the defining characteristics of the genre. Along with the usual heavy metal compositional technique of guitars and bass playing the same riff in unison, this creates an impressively loud and bass-heavy wall of sound. Another defining characteristic is the consistent focus on slow tempos, and minor tonality with much use of dissonance (especially in the form of the tritone).
Traditional doom metal vocalists favour clean vocals, which are often performed with a sense of despair, desperation or pain; imitating the high-tone wails of Ozzy Osbourne (Black Sabbath), Bobby Liebling (Pentagram), and Zeeb Parkes (Witchfinder General). So-called "epic doom" vocalists often take it a step further, singing in an operatic style. Doom metal bands influenced by other extreme metal genres often use growled or screamed vocals, as is the case of death-doom, black-doom, and funeral doom.
Lyrics in doom metal play a key role. Influenced by notable blues musicians like Robert Johnson and Son House, normally they are gloomy and pessimistic, including themes such as: suffering, depression, fear, grief, dread, death and anger. While some bands write lyrics in introspective and personal ways, others convey their themes using symbolism – which may be inspired by occult arts and literature.
Some doom metal bands use religious themes in their music. Trouble, one of the genre's pioneers, were among the first to incorporate Christian imagery. Others have incorporated occult and pagan imagery. For many bands, the use of religious themes is for aesthetic and symbolic purposes only. Examples include lyrics/imagery about the Last Judgment to invoke dread, or the use of crucifixes and cross-shaped headstones to symbolize death.
Furthermore, some doom metal bands write lyrics about drugs or drug addiction. This is most common among stoner doom bands, who often describe hallucinogenic or psychedelic experiences.