Death metal is an extreme subgenre of heavy metal music. It typically employs heavily distorted and low-tuned guitars, played with techniques such as palm muting and tremolo picking; deep growling vocals; aggressive, powerful drumming, featuring double kick and blast beat techniques; minor keys or atonality; abrupt tempo, key, and time signature changes; and chromatic chord progressions. The lyrical themes of death metal may include slasher film-style violence, political conflict, religion, nature, philosophy, true crime and science fiction. Building from the musical structure of thrash metal and early black metal, death metal emerged during the mid-1980s. Bands such as Venom, Celtic Frost, Slayer, and Kreator were important influences on the genre's creation. Possessed, Death, Necrophagia, Obituary, Autopsy, and Morbid Angel are often considered pioneers of the genre. In the late 1980s and early 1990s, death metal gained more media attention as a popular genre. Niche record labels like Combat, Earache, and Roadrunner began to sign death metal bands at a rapid rate.