摘要 |
An encoder is arranged to add a binary code bit to block of a signal by selecting, within the block, (i) a reference frequency within the predetermined signal bandwidth, (ii) a first code frequency having a first predetermined offset from the reference frequency, and (iii) a second code frequency having a second predetermined offset from the reference frequency. The spectral amplitude of the signal at the first code frequency is increase d so as to render the spectral amplitude at the first code frequency a maximum in its neighborhood of frequencies and is decreased at the second code frequency so as to render the spectral amplitude at the second code frequenc y a minimum in its neighborhood of frequencies. Alternatively, the portion of the signal at one of the first and second code frequencies whose spectral amplitude is smaller may be designated as a modifiable signal component such that, in order to indicate the binary bit, the phase of the modifiable signa l component is changed so that this phase differs within a predetermined amoun t from the phase of the reference signal component. As a still further alternative, the spectral amplitude of the first code frequency may be swapp ed with a spectral amplitude of a frequency having a maximum amplitude in the first neighborhood of frequencies and the spectral amplitude of the second code frequency may be swapped with a spectral amplitude of a frequency havin g a minimum amplitude in the second neighborhood of frequencies. A decoder may be arranged to decode the binary bit.
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