The twelve-inch single (often written as 12-inch or 12″) is a type of vinyl (polyvinyl chloride or PVC) gramophone record that has wider groove spacing and shorter playing time with a "single" or a few related sound tracks on each surface, compared to LPs (long play) which have several songs on each side. It is named for its 12-inch (300 mm) diameter that was intended for LPs. This technical adaptation allows for louder levels to be cut on the disc by the mastering engineer, which in turn gives a wider dynamic range, and thus better sound quality. This record type, which is claimed to have been accidentally discovered by Tom Moulton,[1] is commonly used in disco and dance music genres, where DJs use them to play in clubs. They are played at either 33+1⁄3 or 45 rpm. The conventional 7-inch single usually holds three or four minutes of music at full volume. The 12-inch LP sacrifices volume for extended playing time.