Rock DJ (disc jockey)

A disc jockey (abbreviated DJ, D.J. or deejay) is a person who mixes different sources of pre-existing recorded music as it is playing, usually for a live audience in a nightclub or dance club or via broadcasting. Originally, the "disc" in "disc jockey" referred to gramophone records, but now "DJ" is used as an all-encompassing term to describe someone who mixes recorded music from any sources, including cassettes, CDs, or digital audio files on a CDJ or laptop. DJs typically perform for a live audience in a nightclub or dance club or a TV, radio broadcast audience, or in the 2010s, an online radio audience. DJs also create mixes, remixes and tracks that are recorded for later sale and distribution. In hip hop music, DJs may create beats, using percussion breaks, basslines and other musical content sampled from pre-existing records. In hip hop, rappers and MCs use these beats to rap over.

DJs use equipment that can play at least two sources of recorded music simultaneously and mix them together. This allows the DJ to create seamless transitions between recordings and develop unique mixes of songs. Often, this involves aligning the beats of the music sources so their rhythms do not clash when they are played together, either so two records can be played at the same time, or to enable the DJ to make a smooth transition from one song to another. DJ equipment, notably the specialized DJ mixer, a small audio mixer with a crossfader and cue functions. The crossfader enables the DJ to blend or transition from one song to another. The cue knobs or switches allow the DJ to preview a source of recorded music in headphones before playing it for the live club or broadcast audience. Previewing the music in headphones helps the DJ pick the next track they want to play and cue up the track to the desired starting location so it will mix well with the currently playing music. DJs may also use a microphone to speak to the audience; effects units such as reverb to create sound effects; drum machines and synthesizers.

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