Identification/authentication coding method and apparatus

A method of processing audio to convey auxiliary information therewith without audible evidence of audio alteration is provided, in which the audio is represented by digital data, and the auxiliary information comprises a data string having plural bit positions, each with a "1" or "0" value. The method comprises: receiving the plural bit auxiliary data; providing noise data; processing the plural bit auxiliary data and the noise data to yield intermediate data; and summing the intermediate data with the audio data to yield encoded audio; wherein the audio is repeatedly encoded from each of plural non-overlapping excerpts of the encoded audio.