A DJ mixer is a type of audio mixing console used by disc jockeys (DJs). DJs playing music for dancers at a club use the mixer to make smooth transitions between different songs which are played on sound sources that are plugged into the mixer. These sound sources could be turntables, CD players, or iPods. A "scratching" DJ uses the mixer in combination with turntables or specialized DJ CD players to create unique sound effects. The DJ mixer also allows the DJ to use headphones to cue the next song before playing it. Most DJ mixers can only accommodate two turntables or CD players but some mixers (such as the ones used in nightclubs) Can accommodate up to four turntables or CD players.