As music technology has progressed, DJs have adopted different types of equipment to play and mix music, all of which are still commonly used. Traditionally, DJs used two turntables plugged into a DJ mixer to mix music on vinyl records. As compact discs became popular media for publishing music, specialized high quality CD players known as CDJs were developed for DJs. CDJs can take the place of turntables or be used together with turntables. Many CDJs can now play digital music files from USB flash drives or SD cards in addition to CDs. With the spread of portable laptop, tablet, and smartphone computers, DJs began using software together with specialized sound cards and DJ controller hardware. DJ software can be used in conjunction with a hardware DJ mixer or be used instead of a hardware mixer.
Turntables allow DJs to play vinyl records. By adjusting the playback speed of the turntable, either by adjusting the speed knob, or by manipulating the platter (e.g., by slowing down the platter by putting a finger gently along the side), DJs can match the tempos of different records so their rhythms can be played together at the same time without clashing or make a smooth, seamless transition from one song to another. This technique is known as beatmatching. DJs typically replace the rubber mat on turntables that keeps the record moving in sync with the turntable with a slipmat that facilitates manipulating the playback of the record by hand. With the slipmat, the DJ can stop or slow down the record while the turntable is still spinning. Direct-drive turntables are the type preferred by DJs, with the Technics SL-1200 being the most popular model of turntables for DJs. Belt-drive turntables are less expensive, but they are not suitable for turntablism and DJing, because the belt-drive motor does not like being slowed down, as it can stretch out the belt. Some DJs, most commonly those who play hip hop music, go beyond merely mixing records and use turntables as musical instruments for scratching, beat juggling, and other turntablism techniques.
CDJs are high quality digital media players made for DJing. They often have large jog wheels and pitch controls to allow DJs to manipulate the playback of digital files for beatmatching similar to how DJs manipulate vinyl records on turntables. CDJs often have features such as loops and waveform displays similar to DJ software. Originally designed to play music from compact discs, they now can play digital music files stored on USB flash drives and SD cards. Some CDJs can also connect to a computer running DJ software to act as a DJ controller.
Mixers are audio mixing consoles specialized for DJing. Most DJ mixers have far fewer channels than a mixer used by a record producer or audio engineer; whereas standard live sound mixers in small venues have 12 to 24 channels, and standard recording studio mixers have even more (as many as 72 on large boards), basic DJ mixers may have only two channels.
DJs generally use higher quality headphones than those designed for music consumers. DJ headphones have other properties useful for DJs, such as designs that acoustically isolate the sounds of the headphones from the outside environment (hard shell headphones), flexible headbands and pivot joints to allow DJs to listen to one side of the headphones, while turning the other headphone away (so he/she can monitor the mix in the club), and replaceable cables. Replaceable cables enable DJs to buy new cables if a cable becomes frayed, worn, or damaged, or if a cable is accidentally cut.
DJ software can be used to mix audio files on the computer instead of a separate hardware mixer. When mixing on a computer, DJs often use a DJ controller device that mimics the layout of two turntables plus a DJ mixer to control the software rather than the computer keyboard & touchpad on a laptop, or the touchscreen on a tablet computer or smartphone. Many DJ controllers have an integrated sound card with 4 output channels (2 stereo pairs) that allows the DJ to use headphones to preview music before playing it on the main output.
A microphone, so that the DJ can introduce songs and speak to the audience over the sound system.