Abstract: A modulator generates a combined signal consisting of audio and video signals and converts the combined signal to one of a plurality of frequencies in dependence upon a desired output frequency and broadcast standard. The modulator includes a summing amplifier, a first frequency synthesizer and a second frequency synthesizer. The summing amplifier has a first input for receiving a video signal, a second input for receiving a first audio signal, a third input for receiving a second audio signal, and an output for outputting a modulated summed signal. The first frequency synthesizer generates a first frequency for mixing with the modulated summed signal to generate a high intermediate frequency (HI-IF) signal. The second frequency synthesizer generates a second frequency for mixing with said HI-IF signal to generate a desired RF output signal.

Abstract: In a cable television converter terminal, NICAM signal passthrough is achieved using an alignment-free passthrough circuit including a NICAM SAW filter. The alignment-free passthrough circuit directly taps the output of the converter terminal's tuner to obtain the NICAM signal. As a result, the NICAM signal is not distorted by the components involved in obtaining the other signal components of the cable television signal. Consequently, sound quality is improved and rendered less vulnerable to degradation due to component aging, temperature fluctuations, and human error. The passthrough circuit can be implemented as a removable circuit module.

Abstract: In a cable television converter terminal, NICAM signal passthrough is achieved using an alignment-free passthrough circuit including a NICAM SAW filter. The alignment-free passthrough circuit directly taps the output of the converter terminal's tuner to obtain the NICAM signal. As a result, the NICAM signal is not distorted by the components involved in obtaining the other signal components of the cable television signal. Consequently, sound quality is improved and rendered less vulnerable to degradation due to component aging, temperature fluctuations, and human error. The passthrough circuit can be implemented as a removable circuit module.

Abstract: 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 “clear” or “masked” 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 “masked” 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.