Viking metal, and the closely related style pagan metal, is more of a term or "etiquette" than a musical style. Since they are defined chiefly by lyrical focus, any musical categorizations of these two styles is controversial. Thus, Viking metal is more of a cross-genre term than a descriptor of a certain sound. Ashby and Schofield write that "The term 'Viking metal' is one of many that falls within a complex web of genres and subgenres, the precise form of which is constantly shifting, as trends and fads emerge and fade." From its origins in black metal, Viking metal "has diversified (at least in aural terms), and now covers a range of styles that run the gamut between black metal and what one might justifiably term classic rock". Starting with the album Blood Fire Death, one of the first definitive Viking metal releases, Bathory incorporated a diverse range of musical elements. While retaining the noise and chaos of previous recordings, the band took a more sorrowful and melodic approach, working in ballads based on Germanic and Norse folklore, shanty-like melodies and folk music elements such as bourdon sounds, Jew's harps, and fifes. Bathory added natural found sounds, such as ocean waves, thunder, and wild animal noises, in a style similar to that of musique concrète. Instruments were sometimes used to create onomatopoeic effects such as drum sounds imitating thunder or a sledgehammer. The songs typically featured multi-sectional formal structures, following a pattern of three instrumental sections – introduction, bridge, and finale – and two vocal sections – stanza and refrain. Enslaved, a formative band in Viking metal, performs primarily a black metal style, but has over time become more progressive. Eduardo Rivadavia described the hallmarks of Enslaved as "Viking themes, razor sharp guitars, blastbeat drums, and an ear for orchestration resulting in complex structures, bountiful harmonies and time changes." The band evolved significantly with every album since Mardraum – Beyond the Within (2000). The Faroese band Týr has a standard rock band lineup with electric instruments, but makes extensive use of traditional Faroese music in its songs. Faroese ballads typically involve unusual time signatures, most commonly or the alternative rhythms or . In an attempt to replicate these uneven signatures, Týr often places the accent on the weak beat of the bar. In songs based on old Faroese ballads, Týr usually play in harmonic or melodic minor scale or else