Anti-copying system for audio signals

摘要

In order to protect audio signals against copying, the present invention proposes to mix the audio signal with at least one non-audible disturbance signal. A first disturbance signal may be a low-frequency signal which is added to the audio signal, while a second disturbance signal may be a high-frequency disturbance signal which is multiplied with the audio signal. Additionally, the second disturbance signal may be modulated by a modulating signal comprising either the original or inverted original signal, or spoken messages indicative of an illegal copy.