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, 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.