Heavy metal music
Critics disagree over who can be thought of as the first heavy metal band. Most credit either Led Zeppelin or Black Sabbath, with American commentators tending to favour Led Zeppelin and British commentators tending to favour Black Sabbath, though many give equal credit to both. A few commentators—mainly American—argue for other groups including Iron Butterfly, Steppenwolf or Blue Cheer. Deep Purple, the third band in what is sometimes considered the "unholy trinity" of heavy metal (Black Sabbath, Led Zeppelin, and Deep Purple), despite being slightly older than Black Sabbath and Led Zeppelin, fluctuated between many rock styles until late 1969 when they took a heavy metal direction.
Heavy metal music
The first wave of black metal emerged in Europe in the early and mid-1980s, led by the United Kingdom's Venom, Denmark's Mercyful Fate, Switzerland's Hellhammer and Celtic Frost, and Sweden's Bathory. By the late 1980s, Norwegian bands such as Mayhem and Burzum were heading a second wave. Black metal varies considerably in style and production quality, although most bands emphasize shrieked and growled vocals, highly distorted guitars frequently played with rapid tremolo picking, a dark atmosphere and intentionally lo-fi production, with ambient noise and background hiss.