The Importance Of Setting And Maintaining Correct Signal And Modulation Levels In A CATV System Carrying BTSC Stereo Signals (1986)

By Chris Bowick, Scientific-Atlanta, Inc.

There has been much discussion in the recent literature concerning the pro's and con's of carrying BTSC Stereo on a CATV System. The discussions have primarily been associated with one of three subjects:

  1. What is the BTSC format?
  2. How will the CATV system impair stereo performance?
  3. How will the BTSC audio signal impair CATV video performance?

While these discussions have been meaningful and in some cases helpful to the CATV Operator's understanding of how the system works, they have in many cases fallen short of addressing the practicality of setting up the Headend once the operator knows that he will, in fact, be carrying stereo. In this paper, the importance of setting and maintaining correct audio modulation levels, especially with reference to the interface between the BTSC Stereo Encoder and the Video Modulator, will be discussed. This interface is critical to the overall performance of the BTSC system. If the interface is handled incorrectly, stereo performance could be severely impaired, resulting in a multitude of service related calls from a now "stereo-aware" public. No longer will the CATV engineer be able to treat audio as the unimportant portion of the television signal. An increased awareness of audio quality by the public as well as improvements in the state-of-the-art in television stereo processing in the home (VCR's, Stereo Adapters, Stereo TV's), will require that the CATV engineer exercise new levels of caution in the handling of audio information.

Throughout the history of television and certainly throughout the history of CATV, the audio information carried by a television signal has been considered by most of us to be a noncritical item. We simply haven't paid it much attention. After all, the limiting factor in audio quality has always been the consumer's own television set. Why should we be worrying about preserving audio quality in the CATV plant when the customer didn't need or even expect good audio performance out of his set? The answer in most cases is obvious as we have simply ignored audio and have concentrated on providing good quality video to the customer.

But recently, and for several reasons, our customers have become much more aware of the benefits of good quality audio. The Compact Disc Player, Stereo or Hi-Fi VCR and now Stereo TV with its associated barrage of consumer advertising have enlightened the CATV customer to the point that he is beginning to expect and in fact demand "good" stereo-audio performance. This is especially true of the new Stereo-TV owner. Because of this increased customer awareness, the CATV operator must begin to better understand what good audio quality really is and how it can be preserved as it passes through the CATV headend. Our methods of processing a stereo signal in the CATV headend can make the difference between the deliberate transmission of actual stereo or the inadvertant transmission of monaural audio. To make matters even worse, mishandling the stereo signal in the CATV headend can also create poor sounding monaural audio for the vast majority of our current customers who are non-stereo equipped.

This paper, in addition to investigating the importance of modulation levels will outline other key areas of concern to the CATV operator to ensure preservation of the stereo signal.

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