Sludge metal began as a derivative of doom metal, incorporating hardcore punk and elements of Southern rock. Many sludge bands compose slow and heavy songs that contain brief hardcore passages. However, some bands emphasize fast tempos throughout their music. The string instruments are heavily distorted and are often played with large amounts of feedback to produce an abrasive, sludgy sound. Drumming is often performed in typical doom metal fashion, but drummers may employ hardcore d-beat or double-kick drumming during faster passages. Vocals are usually shouted or screamed, and lyrics are generally pessimistic in nature. Suffering, drug abuse, politics and anger towards society are common lyrical themes. New Orleans with its metal scene is often considered as its birthplace. The style was pioneered in the early 1990s by bands such as Eyehategod, Crowbar, Buzzoven and Acid Bath.