DJ mixer in the context of "Nu metal"

A disc jockey, more commonly abbreviated as DJ, is a person who plays recorded music for an audience. Types of DJs include radio DJs (who host programs on music radio stations), club DJs (who work at nightclubs or music festivals), mobile DJs (who are hired to work at public and private events such as weddings, parties, or festivals), and turntablists (who use record players, usually turntables, to manipulate sounds on phonograph records). Originally, the "disc" in "disc jockey" referred to shellac and later vinyl records, but nowadays DJ is used as an all-encompassing term to also describe persons who mix music from other recording media such as cassettes, CDs or digital audio files on a CDJ, controller, or even a laptop. DJs may adopt the title "DJ" in front of their real names, adopted pseudonyms, or stage names.

DJs commonly use audio equipment that can play at least two sources of recorded music simultaneously. This enables them to blend tracks together to create transitions between recordings and develop unique mixes of songs. This can involve aligning the beats of the music sources so their rhythms and tempos do not clash when played together and enable a smooth transition from one song to another. DJs often use specialized DJ mixers, small audio mixers with crossfader and cue functions to blend or transition from one song to another. Mixers are also used to pre-listen to sources of recorded music in headphones and adjust upcoming tracks to mix with currently playing music. DJ software can be used with a DJ controller device to mix audio files on a computer instead of a console mixer. DJs may also use a microphone to speak to the audience; effects units such as reverb to create sound effects and electronic musical instruments such as drum machines and synthesizers.

Turntablism is the art of manipulating sounds and creating new music, sound effects, mixes and other creative sounds and beats, typically by using two or more turntables and a cross fader-equipped DJ mixer. The mixer is plugged into a PA system (for live events) or broadcasting equipment (if the DJ is performing on radio, TV or Internet radio) so that a wider audience can hear the turntablist's music. Turntablists typically manipulate records on a turntable by moving the record with their hand to cue the stylus to exact points on a record, and by touching or moving the platter or record to stop, slow down, speed up or, spin the record backwards, or moving the turntable platter back and forth (the popular rhythmic "scratching" effect which is a key part of hip hop music), all while using a DJ mixer's cross-fader control and the mixer's gain and equalization controls to adjust the sound and level of each turntable. Turntablists typically use two or more turntables and headphones to cue up desired start points on different records (Greasley & Prior, 2013).

Turntablists, often called DJs (or "deejays"), generally prefer direct-drive turntables over belt-driven or other types, because the belt can be stretched or damaged by "scratching" and other turntable manipulation such as slowing down a record, whereas a direct drive turntable can be stopped, slowed down, or spun backwards without damaging the electric motor. The word turntablist is claimed to be originated by Luis "DJ Disk" Quintanilla (Primus, Herbie Hancock, Invisibl Skratch Piklz). After a phone conversation with Disk, it was later popularised in 1995 by DJ Babu to describe the difference between a DJ who simply plays and mixes records and one who performs by physically manipulating the records, stylus, turntables, turntable speed controls and mixer to produce new sounds. The new term coincided with the resurgence of hip-hop DJing in the 1990s.

Scratching, sometimes referred to as scrubbing, is a DJ and turntablist technique of moving a vinyl record back and forth on a turntable to produce percussive or rhythmic sounds. A crossfader on a DJ mixer may be used to fade between two records simultaneously.

While scratching is most associated with hip hop music, where it emerged in the mid-1970s, from the 1990s it has been used in some styles of EDM like techno, trip hop, and house music and rock music such as rap rock, rap metal, rapcore, and nu metal. In hip hop culture, scratching is one of the measures of a DJ's skills. DJs compete in scratching competitions at the DMC World DJ Championships and IDA (International DJ Association), formerly known as ITF (International Turntablist Federation). At scratching competitions, DJs can use only scratch-oriented gear (turntables, DJ mixer, digital vinyl systems or vinyl records only). In recorded hip hop songs, scratched "hooks" often use portions of other songs.

A mixing console or mixing desk is an electronic device for mixing audio signals, used in sound recording and reproduction and sound reinforcement systems. Inputs to the console include microphones, signals from electric or electronic instruments, or recorded sounds. Mixers may control analog or digital signals. The modified signals are summed to produce the combined output signals, which can then be broadcast, amplified through a sound reinforcement system or recorded.

Mixing consoles are used for applications including recording studios, public address systems, sound reinforcement systems, nightclubs, broadcasting, and post-production. A typical, simple application combines signals from microphones on stage into an amplifier that drives one set of loudspeakers for the audience. A DJ mixer may have only two channels, for mixing two record players. A coffeehouse's small stage might only have a six-channel mixer, enough for two singer-guitarists and a percussionist. A nightclub stage's mixer for rock music shows may have 24 channels for mixing the signals from a rhythm section, lead guitar and several vocalists. A mixing console in a professional recording studio may have as many as 96 channels. Consoles used for live sound can go even higher, with some having up to 384 input channels.

A CDJ is a specialized digital music player for DJing. Originally designed to play music from compact discs, many CDJs can play digital music files stored on USB flash drives or SD cards. In typical use, at least two CDJs are plugged into a DJ mixer. CDJs have jog wheels and pitch faders that allow manipulation of the digital music similar to a vinyl record on a DJ turntable. Many have additional features that are not present on turntables, such as looping, beat analysis, and adjusting tempo independently of pitch. Additionally, some can function as DJ controllers to control the playback of digital files in DJ software such as VirtualDJ and Serato.

Many pro audio companies such as Gemini, Denon DJ, Numark, Stanton, and Vestax produced DJ quality CD players. In 1993 Denon DJ was the first to implement a 2-piece rack-mounted dual-deck variable-pitch CD player with a jog wheel and instant cue button for DJs. It quickly became the industry standard and was widely adopted in most clubs and mobile DJs throughout the 90s up until 2004 when Pioneer made an impact with the CDJ-1000. Pioneer DJ CDJs have since become widely regarded as the industry standard.

A DJ mix, DJ mixset or DJ set is a sequence of musical tracks typically mixed together by a DJ to appear as one continuous track. DJ mixes are usually performed using a DJ mixer and multiple sounds sources, such as turntables, CD players, digital audio players or computer sound cards, sometimes with the addition of samplers and effects units, although it is possible to create one using sound editing software.

DJ mixing is significantly different from live sound mixing. Remix services were offered beginning in the late 1970s in order to provide music which was more easily beatmixed by DJs for the dancefloor. One of the earliest DJs to refine their mixing skills was DJ Kool Herc. Francis Grasso was the first DJ to use headphones and a basic form of mixing at the New York City nightclub Sanctuary. Upon its release in 2000, Paul Oakenfold's Perfecto Presents: Another World became the biggest-selling DJ mix album in the US.