The analogue phase alternation line (PAL)-I colour television system, as used in the UK, uses amplitude modulation for the vision carrier and frequency modulation for the monophonic sound channel. The sound carrier is positioned 6 MHz above the vision carrier. In addition to these, the carrier for the near-instantaneous companded audio multiplex (NICAM) stereo version of the same audio programme is located 6.552 MHz above the vision carrier. This stereo information in digital format is superimposed on the subcarrier using a modiﬁ ed form of phase modulation. To avoid adjacent channel interference, this wide band signal is allocated a transmission channel that is 8 MHz wide (an 8 MHz channel spacing). The PAL system is used extensively in Western Europe. The National Television System Committee (NTSC) colour system is used in the USA and Japan, and the French Sequential Couleur À Memoire (SECAM) system is used in France, the former USSR and former French colonies.