Sludge doom (also known as sludge metal) is a style that combines doom metal and hardcore punk. Many sludge bands compose slow and heavy songs that contain brief hardcore passages.However, some bands emphasise 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 often focus on suffering, drug abuse, politics and anger towards society. The style was pioneered in the early 1990s by bands such as Eyehategod, Crowbar, Buzzov*en, Acid Bath and Grief.