Astute observers of ATSC standards may have noticed that in the most recent version of A/52 called A/52B, there is a format called E-AC-3. This is known as Enhanced AC-3, and is commercially known as Dolby Digital Plus. Questions such as "Is this a new version of AC-3?" and "What do I have to do to support this?" are common and justified. The answers are simple and straightforward.
Enhanced AC-3 was developed to extend the capabilities of the AC-3 system to allow for lower data rates (at a given audio quality), for more channels than the standard 5.1, if needed, and some additional audio metadata capabilities. These additions were mostly targeted towards supporting the so-called robust mode, or Enhanced 8-VSB mode for digital television (covered in standard A/52E), but E-AC-3 does not replace the requirement for using standard AC-3 (Dolby Digital) for normal broadcasting. Interestingly, both the HD-DVD and Blu-ray formats support E-AC-3, better known here as Dolby Digital Plus to take advantage of some of these new features.
Importantly, for broadcasters, Dolby Digital Plus is not directly compatible with the large installed base of consumer decoders, which includes not only DTV receivers, but also digital cable set-top boxes. After transmission, it requires conversion to standard AC-3 before it is compatible with standard consumer A/V receivers.
So, in summary, while this technology might start to appear in later generation DTV set-top boxes and receivers, standard Dolby Digital (AC-3) will always be required in transmission to maintain compatibility with the millions and millions of installed receivers and decoders.
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