Patent ID: 6845360

Claim:
A method of encoding audio data with a message, the audio data having a preexisting message encoded therein comprising a sequence of preexisting message symbols, the preexisting message symbols each comprising a distinguishable combination of substantially single-frequency components having frequencies selected from a predefined set of substantially single-frequency values, comprising: providing data defining a plurality of further message symbols each comprising a combination of substantially single-frequency components selected from the predefined set of substantially single-frequency values distinguishable from the combinations of all others of the further message symbols; at least some of the substantially single-frequency components included in the further message symbols having the same frequency as at least some of the substantially single-frequency components included in the preexisting message symbols; and encoding the audio data with a further message comprising a sequence of the further message symbols such that at least some of the further message symbols of the further message coexist with at least some of the preexisting message symbols of the preexisting message along a time base of the audio data.