11. An apparatus for embedding code words within an audio signal, the apparatus comprising: an encoder configured to receive pairs of code words, each pair of code words comprising an ID code word and a synchronisation code word, wherein the ID code words of all of the pairs for a given audio signal are the same and wherein each synchronization code word for the audio signal is unique, the encoder being and configured to encode the code words of each pair of code words separately to form encoded code word signals; and a combiner configured to combine the encoded code word signals with different portions of the received audio signal to form a modified audio signal that carries the pairs of code words distributed within the audio signal.
12. The apparatus according to claim 11 , wherein the pairs of code words are continuously encoded within the audio signal.