By Jeffrey C. Riedmiller, Dolby Laboratories Inc.
With an increasing number of cable systems deploying large volumes of digital set top boxes and digital services it has become increasingly apparent that large audio level discrepancies can exist between analog and digitally tiered programming. Since the local cable system usually has no control over the digital service audio levels it is up to the programmer(s), in most cases, to rectify any of these discrepancies. Programmers offering digital services are able to take advantage of some very unique tools included with their encoding systems to assist with many of these issues. These tools include the generation of audio metadata that is carried within the coded audio bitstream to the digital subscribers set top decoder. In this paper, the impacts of supplying digital programming with “valid” audio metadata vs. “default” or “invalid” audio metadata from the digital cable subscriber’s perspective will be analyzed. However, the proper use of audio metadata by the programmer also assumes that the millions of deployed set top decoders have been designed with a clear understanding of the entire system as well. Recommendations for digital set top designs are needed for the cable industry and will insure that the effort to generate “valid” metadata by programmers will result in the expected behavior within the digital set tops. To this end, a reference model is also proposed in this paper.