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 enhance 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.
