Patent ID: 7006555

Claim:
A method for encoding first and second blocks of information associated with at least a portion of an audio signal with corresponding first and second code portions, comprising: selecting first and second frequencies from a frequency spectrum associated with the first block of information; modulating a characteristic of the audio signal to form a first encoded block of information containing first information associated with the audio signal and information associated with the first code portion at each of the first and second frequencies, without substantially eliminating a portion of the audio signal at one of the first and second frequencies; selecting third and fourth frequencies from a frequency spectrum associated with the second block of information, wherein the third and fourth frequencies are offset from the first and second frequencies; and modulating the characteristic of the audio signal to form a second encoded block of information containing second information associated with the audio signal and information associated with the second code portion at each of the third and fourth frequencies, wherein modulating the characteristic of the audio signal includes increasing the spectral power at one of the first and second frequencies to render the spectral power at the one of the first and second frequencies a local maximum and decreasing the spectral power at the other of the first and second frequencies to render the spectral power at the other of the first and second frequencies a local minimum, and wherein modulating the audio signal includes increasing the spectral power at one of the third and fourth frequencies to render the spectral power at the one of the third and fourth frequencies a local maximum and decreasing the spectral power at the other of the third and fourth frequencies to render the spectral power at the other of the third and fourth frequencies a local minimum.