Both HD disc formats possess an audio sophistication dramatically greater than that of standard-definition DVD-Video. For example, rather than simply delivering a commentary track on the disc, the new formats might construct a commentary enhanced track using the main soundtrack from the movie, mixed with a commentary track downloaded from the Internet. These elements will be mixed in the player to create the final audio presentation.
The implications of this are significant. Aside from the obvious aspect that new features can be created for a given title long after the discs have shipped, the fact that players will be mixing the audio internally means that it will no longer be possible to output the raw bitstreams from the player as is customary with DVD-Video. Instead, these players will decode and mix in standard PCM format, and therefore will have the option to output the PCM digital signal either directly, or through DACs as analog signals to the connected audio receiver. It should be mentioned that certain discs and players will indeed support the direct output of encoded audio bitstreams, but this option is the choice of the content maker.
Many advanced A/V receivers and processors manufactured today have six (or even eight) channels of external analog audio input for high-resolution DVD-Audio or SACD playback; these will work equally well for multichannel analog-equipped HD disc players, and enable consumers to take advantage of the full-bandwidth audio performance available in nextgeneration formats without having to upgrade their A/V systems. A growing number of A/V receivers include HDMI™ (1.1) inputs, providing a direct digital connection for the new optical disc players. This ensures not only that the full quality of the HD formats will be available, but that any digital postprocessing—such as bass management, room compensation, speaker equalization, Dolby Pro Logic® IIx processing, and others—can be performed in the A/V processor directly on the source audio without any extra analog and digital conversion steps along the way.
One additional consequence of the above rapidly becomes apparent: there will be no particular reason or benefit to decoding native audio bitstreams in the A/V receiver. This means A/V receivers with HDMI digital inputs or analog-to-digital converters for their analog inputs will be able to use their DSP resources to postprocess full-bandwidth audio from the players, rather than being required to also handle core bitstream decoding duties. (Such postprocessing is often done at a sampling rate of 96 kHz, thereby demanding at least double the DSP horsepower of conventional postprocessing done at 48 kHz.)
