| 摘要 |
In a transmission, encoding or recording system for use with audio signals, a selected frequency component of the audio signal is removed and replaced by a substitute component which is synthesized from the rest of the audio signal and is modulated in dependence upon the data to be transmitted. The additional data can then be made imperceptible and the audio signal can still be processed as before, while the additional data can be readily detected. At the transmitter (12), a predictor (24) synthesizes a selected frequency component from the rest of the audio signal. The synthesized component is modulated by the data in a modulator (26), and combined in a combiner (30) with the original signal from which the selected frequency component has been removed by a band-stop filter (22). At the receiver (14, Fig. 2), a like predictor (46) can generate the same synthesized signal for comparison with the corresponding component of the transmitted signal selected by a band-pass filter (44), the two combined in a subtractor (48) and the difference detected by a correlator (50) to retrieve the added data. |
