By David A. Sedacca, Scientific-Atlanta
Presented is a summary of significant experience with BTSC stereo, with elaboration on areas where operators must make decisions critical to system performance. The acquisition of audio source material In the headend is possible by several means. Formats include various satellite subcarrier systems, scrambled satellite transmissions, and locally supplied audio feeds. Operators often need automatic switching for redundancy or commercial message insert ion. Several methods are available for the transportation of stereo from the earth station to the headend. Some cable operators use FM links or AM links to connect various distribution systems, which may pose special problems when stereo is used. Audio input levels to the encoder must be set. Apparent loudness, peak deviation, and average levels are explained. The role of audio signal processing is discussed. Manufacturers provide multiple options for interfacing the stereo encoder with the headend modulator. Sources of error and performance degradation are cited, with techniques of minimizing them. CATV scrambling systems can affect separation and noise performance. Subscriber equipment can cause the most degradation to the BTSC stereo signal. Performance characteristics for various consumer decoders are described. There are several useful techniques for system evaluation. Complete checks require interruption of service, though basic operation can be verified while on line.