A DJ mixer is a type of audio mixing console

Mixing console

In professional audio, a mixing console, or audio mixer, also called a sound board, mixing desk, or mixer is an electronic device for combining , routing, and changing the level, timbre and/or dynamics of audio signals. A mixer can mix analog or digital signals, depending on the type of mixer...

 used by disc jockey

Disc jockey

A disc jockey, also known as DJ, is a person who selects and plays recorded music for an audience. Originally, "disc" referred to phonograph records, not the later Compact Discs. Today, the term includes all forms of music playback, no matter the medium.There are several types of disc jockeys...

s.
The key features that differentiate a DJ mixer from other types of audio mixers are the ability to redirect (cue) a non-playing source to headphones

Headphones

Headphones are a pair of small loudspeakers, or less commonly a single speaker, held close to a user's ears and connected to a signal source such as an audio amplifier, radio, CD player or portable Media Player. They are also known as stereophones, headsets or, colloquially, cans. The in-ear...

 and the presence of a crossfader, which allows for an easier transition between two sources. DJ mixers are also used to create DJ mix

DJ mix

A DJ mix or DJ mixset is a sequence of musical tracks typically mixed together to appear as one continuous track. When a DJ mix or DJ mixset is recorded onto some medium, it is often referred to as a mix tape...

es.

Structure

A typical modern DJ mixer generally has between two and six stereo

Stereophonic sound

The term Stereophonic, commonly called stereo, sound refers to any method of sound reproduction in which an attempt is made to create an illusion of directionality and audible perspective...

 channels for connecting and mixing

Audio mixing (recorded music)

In audio recording, audio mixing is the process by which multiple recorded sounds are combined into one or more channels, most commonly two-channel stereo. In the process, the source signals' level, frequency content, dynamics, and panoramic position are manipulated and effects such as reverb may...

 audio sources. Each channel usually has a phono input with RIAA equalization

RIAA equalization

RIAA equalization is a specification for the correct recording of gramophone records, established by the Recording Industry Association of America...

 for turntable

Phonograph

The phonograph record player, or gramophone is a device introduced in 1877 that has had continued common use for reproducing sound recordings, although when first developed, the phonograph was used to both record and reproduce sounds...

s and one or two line level

Line level

Line level is a term used to denote the strength of an audio signal used to transmit analog sound between audio components such as CD and DVD players, TVs, audio amplifiers, and mixing consoles, and sometimes MP3 players....

 inputs for sources such as CD players. Controls for individual channels are arranged in vertical columns (channel strips), starting with a switch or a knob selecting between the inputs.
Below the input selector is a gain

Gain

In electronics, gain is a measure of the ability of a circuit to increase the power or amplitude of a signal from the input to the output. It is usually defined as the mean ratio of the signal output of a system to the signal input of the same system. It may also be defined on a logarithmic scale,...

 (or trim) control, used to match signal levels between channels. Next follows an equalizer

Equalization (audio)

Equalization is the process commonly used in sound recording and reproduction to alter the frequency response of an audio system using linear filters. Most hi-fi equipment uses relatively simple filters to make bass and treble adjustments. Graphic and parametric equalizers have much more...

 section, used to fade

Fade (audio engineering)

In audio engineering, a fade is a gradual increase or decrease in the level of an audio signal. The term can also be used for film cinematography or theater lighting, in much the same way ....

 parts of tracks in and out; a common basic technique is to kill the bass on one channel while mixing so the bassline

Bassline

A bassline is the term used in many styles of popular music, such as jazz, blues, funk, dub and electronic music for the low-pitched instrumental part or line played by a rhythm section instrument such as the electric bass, double bass, tuba or keyboard...

s of two tracks don't clash. A typical mixer features separate knobs for the low, mid and high frequency ranges. Some more controls may follow, such as a balance knob, built-in sound effect

Sound effect

For the album by The Jam, see Sound Affects.Sound effects or audio effects are artificially created or enhanced sounds, or sound processes used to emphasize artistic or other content of films, television shows, live performance, animation, video games, music, or other media...

s and aux-send

Aux-send

An aux-send is an electronic signal-routing output used on multi-channel sound mixing consoles used in recording and broadcasting settings and on PA system amplifier-mixers used in music concerts...

s for external effects unit

Effects unit

Effects units are electronic devices that alter how a musical instrument or other audio source sounds. Some effects subtly "color" a sound, while others transform it dramatically. Effects are used during live performances or in the studio, typically with electric guitar, keyboard and bass...

s. Below there's normally a cue switch sending the signal to the headphones, letting the DJ preview and beatmatch

Beatmatching

Beatmatching is a disc jockey technique of pitch shifting or timestretching a track to match its tempo to that of the currently playing track e.g. the kicks and snares in two house records hit at the same time when both records are played simultaneously...

 a track without sending it to the master output

Output

Output is the term denoting either an exit or changes which exit a system and which activate/modify a process. It is an abstract concept, used in the modeling, system design and system exploitation.-In control theory:...

, but on some mixers there's a different way to select the cued source. The channel strip ends with a fade

Fade (audio engineering)

In audio engineering, a fade is a gradual increase or decrease in the level of an audio signal. The term can also be used for film cinematography or theater lighting, in much the same way ....

r which sets the channel's signal volume in the final mix.
The signal may pass through a crossfader. On simple mixers there are normally two channels assigned opposite ends of the crossfader, sometimes with a button to reverse the crossfader's direction. More advanced mixers have assignable crossfaders in which each channel can be assigned to either end of the crossfader or to bypass the crossfader entirely. Many scratch mixers have a crossfader curve control that effectively changes the distance the crossfader needs to travel to open the channel fully, letting to shorten it to a millimetre or two, which is useful for speedy scratching

Scratching

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 late 1980s, it has been used...

.

Additionally, one or two microphone

Microphone

A microphone is an acoustic-to-electric transducer or sensor that converts sound into an electrical signal. In 1877, Emile Berliner invented the first microphone used as a telephone voice transmitter...

 inputs may be present to accommodate MCs. These can be configured either as additional inputs to main channels or as special microphone channels which are similar in structure, but normally have fewer controls and are often monaural

Monaural

Monaural or monophonic sound reproduction is single-channel. Typically there is only one microphone, one loudspeaker, or channels are fed from a common signal path...

.
Most DJ mixers feature peak meter

Peak meter

A peak meter is a type of visual measuring instrument that indicates the instantaneous level of an audio signal that is passing through it...

s to aid matching levels between channels and monitor the signal for clipping

Clipping (audio)

Clipping is a form of waveform distortion that occurs when an amplifier is overdriven and attempts to deliver an output voltage or current beyond its maximum capability...

. Usually there are peak meters for master mix and cued mix, though sometimes per-channel meters are present.
A DJ mixer has one or two headphone jack plugs and a headphone volume control. Headphones are normally used to monitor a cued channel, but on some mixers other variants are possible, such as split cue where cued channels are sent to the left headphone channel and master mix to the right, or a way to select between cued channels and master mix.
Normally there are two or more outputs for the master mix, used to send the signal to an amplifier

Amplifier

Generally, an amplifier or simply amp, is a device for increasing the power of a signal.In popular use, the term usually describes an electronic amplifier, in which the input "signal" is usually a voltage or a current. In audio applications, amplifiers drive the loudspeakers used in PA systems to...

 or another mixer for the public address

Public address

A public address system is an electronic amplification system with a mixer, amplifier and loudspeakers, used to reinforce a sound source, e.g., a person giving a speech, a DJ playing prerecorded music, and distributing the sound throughout a venue or building.Simple PA systems are often used in...

 system, to a loudspeaker

Loudspeaker

A loudspeaker is an electroacoustic transducer that produces sound in response to an electrical audio signal input. Non-electrical loudspeakers were developed as accessories to telephone systems, but electronic amplification by vacuum tube made loudspeakers more generally useful...

 in the DJ booth for monitoring the mix, or to a tape recorder

Tape recorder

An audio tape recorder, tape deck, reel-to-reel tape deck, cassette deck or tape machine is an audio storage device that records and plays back sounds, including articulated voices, usually using magnetic tape, either wound on a reel or in a cassette, for storage...

 or a computer

Computer

A computer is a programmable machine designed to sequentially and automatically carry out a sequence of arithmetic or logical operations. The particular sequence of operations can be changed readily, allowing the computer to solve more than one kind of problem...

 for recording. There may be one volume control for all outputs or separate controls for each outputs. Sometimes a recording output doesn't have a volume control.

History

One of the pioneers of DJ mixing equipment design was Rudy Bozak

Rudy Bozak

Rudolph Thomas Bozak was an audio electronics and acoustics designer and engineer in the field of sound reproduction. His parents were Bohemian Czech immigrants; Rudy was born in Uniontown, Pennsylvania. Bozak studied at Milwaukee School of Engineering; in 1981, the school awarded him an honorary...

.

Beatmatching and beatmixing

Beatmixing

Beatmixing is a disk jockey technique of playing two songs at the same time so that the beats of one song occur at the same time as the other.-History:...

 with a DJ mixer were first used to ensure dancers didn't leave the dancefloor between songs.

More recently DJ mixers have been used to for harmonic mixing

Harmonic mixing

Harmonic mixing or key mixing is a DJ's continuous mix between two pre-recorded tracks that are most often either in the same key, or their keys are relative or in a subdominant or dominant relationship with one another....

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