General Instrument Corporation

Motorola Corporation

General Instrument Corporation of Delaware

Henry S Landgraf

Anthony Troiano

Richard Westerfer

Dipakkumar R Patel

Vijay K Pola

A monaural and stereo audio signal control system for use in cable-signal set-top boxes selects signal processing paths as a function of the monaural and stereo nature of the incoming audio component of the television signal and an indication as to whether the audio component is a &ldquo;clear&rdquo; or &ldquo;masked&rdquo; signal. A clear audio signal is a signal that conforms to a NTSC or BTSC standard that can be processed by a conventional television receiver while a &ldquo;masked&rdquo; signal is one in which the carrier frequency has been changed or otherwise modified so that a conventional television receiver cannot extract the audio content. A signal-processing path is provided for conventional clear monaural and stereo audio and for a masked monaural signal and for a masked stereo signal. Monaural clear and masked processing is addressed by microprocessor controlled switching in accordance with control information provided in the television signal and stereo masked processing is addressed by the presence or absence of energy corresponding to the masked stereo carrier.

Monaural and stereo audio signal control system

A method and apparatus allow the function circuitry of a set top box to be readily upgraded or replaced in the field. Replacement or upgraded function circuitry is provided in a self-contained module. The set top box is provided with a port through which the module can be electrically connected to the set top box. Insertion of the module either bypasses existing function circuitry or is the only function circuitry available to the set top box.

Method and apparatus for upgrading features and functions of a set top

Suppressed synchronizing signals of a scrambled standard TV picture are recovered and the picture unscrambled by a method including the steps of: separating a video portion having suppressed sync signals from an audio portion of a TV picture at an intermediate frequency level, amplifying the video portion through a gain controlled amplifier, selectively compensating for the suppressed levels of sync signals, passing the video portion with recovered sync signals of the TV picture through a demodulator, and providing a feedback signal from the demodulator to the gain controlled amplifier to automatically control its gain and thereby minimize artifacts in the TV picture after sync recovery. This new method is easily carried out by apparatus using only a few standard circuit components which can be manufactured as an application specific integrated circuit (ASIC).

Method and apparatus for recovering synchronizing signals in scrambled

In order to defeat pirate descramblers that detect the occurrence of a vertical blanking interval from a gap in timing data provided on the sound carrier of a scrambled television signal, diversionary pulse information is inserted into the sound carrier during the vertical blanking interval. A pirate descrambler that looks for a gap in data transmitted on the sound carrier will then detect a 'false' second gap, and incorrectly phase lock its horizontal oscillator to random video instead of to horizontal timing information that is recoverable during the vertical blanking interval.

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Cherry Hill, NJ, United States of America

Henry S Landgraf