An essential part of DJ equipment is the mixer. This piece of audio equipment allows the DJ to cue a non-playing source of music through headphones into a playing source of music. This allows the DJ to make a smooth transition from one audio source to another through the crossfader on the mixer.

A modern DJ equipment mixer has between two and six stereo channels for connecting up to music sources such as vinyl turntables, CD turntables or a laptop with digital sound recordings. Other elements in the mixer include gain or trim control which is used to match signal levels between channels. There is also an equalizer section which is used to fade in and out parts of tracks. Other extra features can include a balance control, sound effects and aux-sends for external effects units. The cue switch is essential as it allows the DJ to hear the track that he is about to mix into the playing track without the audience hearing the record. This then is mixed using the crossfader once the DJ has used his skill to match up the beat of the two tracks and merge them together and eventually fade out the initially playing track into the new track.

Once again technology has begun to change this previous system that has been used for many years as a part of DJ equipment. The new programs that have arrived on the market actually have a virtual mixer where the computer DJ can have all the abilities of an actual physical mixer built into a PC.