Abstract: Unauthorized duplication of recorded audible program material upon magnetic tape, commonly known as tape piracy, is prevented and rendered detectable by the present method and apparatus for preparing the program material. The method and apparatus prepare recorded audible program material by generating a high frequency modulated signal which varies in a predetermined manner over a selected spectrum of frequencies, and by recording the modulated signal together with the audible program material so that subsequent copying of the program material and modulated signal onto magnetic tape with conventional high frequency bias will produce on the copied tape detectable and identifiable interference signals arising between the modulated signal and the conventional recording bias. The modulated signal may sweep a range of frequencies at a rate which will produce an audible playback noise spoiling the copied tape, and the modulated signal can be coded to identify the origin of the program material.

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.