A disc jockey (abbreviated D.J. or DJ) is a person who plays recorded music for an audience. Originally, "disc" (sometimes spelled "disk", although this is now uncommon) 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. Radio DJs or radio personalities introduce and play music that is broadcast on AM, FM, shortwave, digital or internet radio stations. Club DJs select and play music in bars, nightclubs or discothèques, or at parties or raves, or even in stadiums. Hip hop DJs select and play music using multiple turntables to back up one or more MCs/rappers, perform turntable scratching to create percussive sounds, and are also often music producers who use turntablism and sampling to create backing instrumentals for new tracks. In reggae, the DJ (deejay) is a vocalist who raps, "toasts", or chats over pre-recorded rhythm tracks while the individual choosing and playing them is referred to as a selector.[1] Mobile DJs travel with portable sound systems and play recorded music at a variety of events. Some mobile DJs also serve as the master of ceremonies or MC directing the attention of attendees, and maintaining a room-wide focus on what is included in the event's agenda.[2] According to a 2012 study, there are approximately 1¼ million professional disc jockeys in the world.[3]

The title "DJ" is also commonly used by DJs in front of their real names or adopted pseudonyms as a title to denote their profession and the music they play

Hardtechno refers to a style of Techno, which evolved after 2000 from Schranz and Hardcore Techno. While the first harder Techno productions appeared around 1991 on labels such as PCP and Industrial Strength, these were referred to as Hardcore Techno. Over the years, the Hardcore scene cultivated a new sound far away from its Techno origins, whereas Techno itself went in a softer direction.

At the end of the 1990s, fueled by the Schranz movement, a new, extremely hard style of Techno became popular, which is now generally referred to as Hardtechno. This style runs at very high bpm, usually 150 or more and features heavy distortion and prominent kickdrums. By 2007, almost all major European Techno festivals, such as I Love Techno, Awakenings, MayDay, Nature One, Mystery Land featured a Hardtechno stage or at least one Hardtechno artist. It has also been the main focus of festivals like "Hardtechno Festival" in Vienna (attendance 2,000+) or Syndicate in Dortmund (attendance 10,000).

Deep house was largely pioneered by Chicago producers such as Marshall Jefferson (On The House) and Larry Heard (Mr. Fingers) and with tracks such as "Mystery of Love" (1985) and "Can You Feel It?" and (1986);[1] the latter had a similar impact on deep house as Derrick May's "Strings Of Life" (1987) did on Detroit techno.[2] Heard's deep house sound moved house music away from its posthuman tendencies back towards the lush soulful sound of early disco music (particularly that of old Philadelphia International and Salsoul records).[3]

Later period deep house tracks (1993—94) were more heavily influenced by disco and even merged into a disputable disco house genre.[citation needed] Modern deep house (post-2000) often shares features with the related genre of tech house but tends to focus on musical complexity where tech house focuses on simplicity.[citation needed]

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