Digital audio in early HD disc players

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Digital Audio in Early HD Disc Players
Written by Dan Ramer

Monday, 17 April 2006

Some disturbing details

We’ve discussed the issues concerning early implementations of AACS and the interactive layer in previous columns. Now comes word that the initial players may not be fully functional when it comes to the advanced audio CODECs made part of the specifications for HD DVD and Blu-ray Disc.

Before I jump into the audio, I’ll mention that some of you have written me about the availability of 1080p over HDMI 1.1, the version expected in the initial players from both camps. Some of you wrote expressing concerns that 1080p wouldn’t be available until version HDMI 1.3 is released. It’s my understanding that 1080p can be carried over HDMI 1.1 and both Sony and Samsung have gone out of their ways to point out that their first Blu-ray Disc players will output 1080p over HDMI. The bad news is that HDMI 1.1 is going to get in the way of outputting full audio fidelity. And as I’ve already written, the players’ internal decoding capabilities are limited to 5.1 channels, so the center surround channel of ES and EX mixes will be mixed in the left and right surround channels.

In a recent article by Joseph Palenchar in the consumer electronics trade magazine TWICE, he describes the expected audio capabilities of the two HD disc limitations in great detail.

HD DVD Audio

Neither Dolby Digital 5.1 nor DTS 5.1 are included in the disc’s audio specifications. Dolby Digital Plus is mandatory. DTS HD is mandatory but this audio bit stream will be converted on the fly to 1.5 Mb/s DTS for driving existing DTS decoders via an S/PDIF connection. DTS HD has optional channel formats of 5.1, 6.1, and 7.1 at up to 3 Mb/s in the specification for HD DVD, but neither of the initial Toshiba players has more than 5.1 internal decoding. Dolby True HD in the two-channel mode is mandatory, and optional are 5.1, 6.1, and 7.1 channel formats at up to 96 KHz 24-bit resolution, but again, the initial Toshiba players are limited to 5.1 analog outputs. Also optional is DTS HD Master in up to 5.1 channels and up to 192 KHz 24-bit resolution. Palenchar’s article says that PCM is not included, but Toshiba’s brochures for the players says that up to 5.1 Linear PCM will be available via HDMI.

So it would seem that for the Toshiba HD-XA1 and HD-A1 HD DVD players, if you want the EX or ES center surround experience, you’ll have two choices: accept the audio in DTS 5.1 digital form over an S/PDIF connection to your existing ES decoder and allow it to dematrix the center surround; or, accept the potentially higher fidelity of the players’ internal decoding to analog and use an external decoder to generate the center surround. I’ll discuss the second option in much greater detail in a reworked Pseudo-EX piece based on work I published on the site several years ago. You’ll have to wait until I can lay my hands on an HD disc player first.

Blu-ray Disc Audio

Blu-ray Disc is more versatile, in that it offers far more choices, but only three are mandatory. Both of the familiar Dolby Digital 5.1 and DTS 5.1 are mandatory, and this implies that 6.1 channel formats are available with external decoding since these are available over S/PDIF. The only other mandatory audio format will be 5.1-channel PCM at up to 192 KHz sampling rate with 24-bit resolution. PCM will be available over an HDMI 1.1 connection to a suitable external decoder. DTS HD in up to 7.1 channels at 3 Mb/s, Dolby True HD in up to 7.1 channels at up to 96 KHz with 24-bit resolution, 7.1 channels of PCM up to 96 KHz and 24-bit resolution, and DTS HD Master with up to 5.1 channels and up to 192 KHz with 24-bit resolution are all optional.

But once again, the internal decoder on the initial Blu-ray Disc players will only provide 5.1 analog channels. And the decoder will only handle the mandatory audio CODECs, not the optional CODECs. So to either enjoy the benefits of the center surround will require external decoding, just as with the Toshiba players.

The Downside

But here are the kickers. The really bad news is that, with the exception of PCM, the initial Sony player will not support advanced CODECs either by decoding with its internal decoder or by outputing those digital bit streams for external decoding.

Until HDMI 1.3 becomes available, you will not be able to send the bit streams for the advanced CODECs to an external decoder. So those of us who purchase the earliest HD DVD and Blu-ray Disc players will not have access to the full fidelity audio the format is capable of producing, even after we buy a new decoder that supports all the CODECs and is equipped with HDMI 1.3 connections.

Can the players be upgraded with a firmware change? I have no idea. But I’ll be glad to ask.