| 摘要 |
An improved method and apparatus for maintaining concealment for a scrambled signal when frequency pre-emphasis is used to defeat the scrambling. The pre-emphasis may be synthesized with high pass or peaking circuitry. More commonly however the pre-emphasis is available in television sets with a fine tuning control. By adjusting the fine tuning control to cause purposely mistuning off center, a peaking effect is generated which is used to counter the scrambled signal. The application discloses one embodiment which uses de-emphasis to counter the peaking effect. In another embodiment, signals added in the vicinity of the horizontal blanking interval causes the peaking effect to enhanced these added signals over stable edges of the video signal. Since these added signals are position modulated for example, the television's sync circuits and horizontal oscillator circuits will cause scan circuits to generate position modulation. Thus adding a specific type of signal causes the peaking circuit to enlarge the added signals more than the other parts of the video signal for synchronization. |
