Most electro is instrumental, but a common element is vocals processed through a vocoder. Additionally, speech synthesis may be used to create robotic or mechanical lyrical content, as in the iconic Planet Rock and the automatous chant in the chorus of Nunk by Warp 9. Although primarily instrumental, early electro utilized rap. Male rap dominated the genre, however female rappers are an integral part of the electro tradition, whether featured in a group as in Warp 9 or as solo performers like Roxanne Shante. The lyrical style that emerged along with electro became less popular by the 1990s, as rapping continued to evolve, becoming the domain of hip hop music.