<p>The method involves encoding the signal in accordance with a given encoding process, including feeding back the encoded signal to control the encoding. The encoded signal is modified to represent the supplemental data, and the feeding back of the encoded signal is carried out after the signal modification. The encoding is preferably a unit bit encoding, with sigma delta modulation. The modification of the encoded signal may comprise the replacement of selected samples of the encoded signal by samples of the supplemental data.</p>
