12-inch
The 12-inch single (often simply called 12″) is a type of gramophone record that has wider groove spacing and shorter playing time compared to typical LPs. This allows for louder levels to be cut on the disc by the cutting engineer, which in turn gives a wider dynamic range, and thus better sound quality. This record type is commonly used in disco and dance music genres, where DJs use them to play in discos or clubs. They are played at either 33 1⁄3 or 45 rpm.
12-inch singles typically have much shorter playing time than full-length LPs, thus require fewer grooves per inch. This extra space permits a broader dynamic range or louder recording level as the grooves' excursions (i.e., the width of the groove waves and distance traveled from side to side by the turntable stylus) can be much greater in amplitude, especially in the bass frequencies so important for dance music. Many record companies began producing 12-inch (30 cm) singles at 33 1⁄3 rpm, although 45 rpm gives better treble response and was used on many 12-inch singles, especially in the UK.
The gramophone records cut especially for dance-floor DJs came into existence with the advent of recorded Jamaican mento music in the 1950s. By at least 1956 it was already standard practice by Jamaican sound systems owners to give their "selecter" DJs acetate or flexi disc dubs of exclusive mento and Jamaican rhythm and blues recordings before they were issued commercially. Songs such as Theophilus Beckford's "Easy Snappin'" (recorded in 1956) were played as exclusives by Sir Coxson's Downbeat sound system for years before they were actually released in 1959 – only to become major local hits, also pressed in the UK by Island Records and Blue Beat Records as early as 1960. As the 1960s creativity bloomed along, and with the development of multitrack recording facilities, special mixes of rocksteady and early reggae tunes were given as exclusives to dancehall DJs and selecters. With the 1967 Jamaican invention of remix, called dub on the island, those "specials" became valuable items sold to allied sound system DJs, who could draw crowds with their exclusive hits. The popularity of remix sound engineer King Tubby, who singlehandedly invented and perfected dub remixes from as early as 1967, led to more exclusive dub plates being cut. By then 10-inch records were used to cut those dubs. By 1971, most reggae singles issued in Jamaica included on their B-side a dub remix of the A-side, many of them first tested as exclusive "dub plates" on dances. Those dubs basically included drum and bass-oriented remixes used by sound system selecters. The 10-inch acetate "specials" would remain popular until at least the 2000s (decade) in Jamaica. Several Jamaican DJs such as DJ Kool Herc exported much of the hip hop dance culture from Jamaica to the Bronx in the early 1970s, including the common Jamaican practice of DJs rapping over instrumental dub remixes of hit songs (See King Stitt, U Roy, Dennis Alcapone, Dillinger), ultimately leading to the advent of rap culture in the United States. Most likely, the widespread use of exclusive dub acetates in Jamaica also led American DJs to do the same.
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