Dynamic magnetic information storage or retrieval – Modulating or demodulating
Patent
1975-07-30
1977-08-02
Canney, Vincent P.
Dynamic magnetic information storage or retrieval
Modulating or demodulating
360 15, 360 30, G11B 502, G11B 586
Patent
active
040400999
ABSTRACT:
Unauthorized duplication of recorded program material upon magnetic tape, commonly known as tape piracy, is rendered detectable by the present method and apparatus for preparing the program material. The method and apparatus prepare recorded audible program material by eliminating narrow low and high frequency bands of signals from the program material, inserting a preselected low frequency signal in the low frequency band, modulating a predetermined high frequency signal with the low frequency signal, and inserting the modulated high frequency signal in the high frequency band. Subsequent copying of the recorded program material having these inserted signals will introduce a phase shift between the low and high frequency inserted signals.
Such a phase shift is detected by a method and apparatus which recover the signal recorded upon the magnetic tape recording suspected to be a duplicate, and filter the recovered signal to detect signals within the high and low frequency bands. Signals in the high frequency band are demodulated, and the low frequency signal obtained upon demodulation has its phase compared with the phase of the signal from the low frequency band to detect phase shifts therebetween arising upon duplication with conventional magnetic tape recording equipment. The inserted signals may be coded in a fashion identifying the origin of the program material, or may be inserted during the presence of program material with suitable masking properties. The low frequency signal may itself be modulated to prevent its discrete erasure by the tape pirate.
REFERENCES:
patent: 2622155 (1952-12-01), Dutton
patent: 2774056 (1956-12-01), Stafford et al.
patent: 3070670 (1962-12-01), Eldridge et al.
patent: 3072753 (1963-01-01), Goldberg
patent: 3298006 (1967-01-01), Milenkovic et al.
patent: 3551608 (1970-12-01), Balint
Canney Vincent P.
Cook Laboratories, Inc.
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