s that give rise to multipath fading--variations in RF signal level due to signal reflections. The improved robustness of digital radio promises to remedy this, delivering near-CD sound for most listening conditions. With AM radio, the transition will be even more marked. The new digital service will offer two-channel stereo sound and greatly increased frequency response, resulting in audio quality comparable to today's analog FM. In addition, digital will greatly enhance terrestrial radio robustness, which is the ability to withstand factors such as multipath fading, environmental noise, and impulse noise interference due to automobile ignitions or home appliances. Digital's robustness also holds up well against interference from nearby radio broadcast signals and terrain blockage for FM, as well as signal attenuation due to grounded conductive structures like reinforced-concrete highway overpasses for AM. With most radio listening done in a moving car, the signal degradation varies constantly with time, further complicating matters. To reduce or eliminate these problems, a variety of signal-processing techniques (described below) have been incorporated into digital radio systems. While enhanced quality and robustness and new services entice broadcasters, and should bode well for a smooth transition to digital, another, less tangible reason for making this transition involves consumer perception. Terrestrial radio is one of the few remaining analog communications services in an ever more digital world. With the advent of SDARS, radio in the United States faces a direct digital competitor, and even though SDARS will not provide a locally oriented service like traditional radio, the inevitable comparison of technologies will have "old-fashioned analog radio" coming up on the short end of the stick. It's taken 10 long years, but finally, later this year, two U.S. SDARS systems will begin commercial operation. These t...
