Scratching is a DJ or turntablist technique used to produce distinctive sounds by moving a vinyl record back and forth on a turntable while optionally manipulating the crossfader on a DJ mixer. While scratching is most commonly associated with hip hop music, since the mid-1970s, it has been used in some styles of pop and nu metal. Within hip hop culture, scratching is one of the measures of a DJ's skills, as in DMC World DJ Championship or IDA (International DJ Association) former ITF (International turntablist Federation) where the DJs can use only scratch oriented gears (turntables + mixer + digital vinyl systems or vinyl only, and there are many scratching competitions. In recorded hip-hop songs, scratched hooks often use portions of different rap songs.