Toshiba HD-XA1 HD DVD Player: Hook Me Up Page 3
The last option for extracting surround sound audio from the HD-XA1 is via the traditional coaxial or optical digital audio outputs - otherwise known as the SPDIF outputs. Here's where things get a little odd. To go from its internal PCM mix to SPDIF, which doesn't have enough bandwidth to carry multichannel PCM, a player must actually re-encode the audio to a Dolby Digital or DTS bitstream. But the HD DVD specfications allow the manufacturer to downconvert to either of the two formats or to give the user the option to select one or the other as a default.
For the HD-XA1 (and HD-A1), Toshiba elected to re-encode to DTS only. This means that if you play an HD DVD that has a Dolby Digital Plus soundtrack and listen to it via the player's coax or optical output, your A/V receiver will actually be getting a DTS bitstream from the player, and its front panel will indicate, accurately, that it is playing back DTS.
Once you understand what's happening you'll adjust to it, but it's a little surreal the first time a Dolby soundtrack flashes up on your receiver as DTS. And if you have any insight into the passionate rivalry between these two companies, you'll really appreciate the irony. But this happens only with HD DVDs - pop a regular DVD into the HD-XA1, and it will pass through the standard Dolby Digital or DTS bitstream on the disc, just like any other DVD player.
In any event, it's worth noting that, because the audio signal on the disc starts out at a higher bit rate, the DTS or Dolby Digital bitstream put out by an HD DVD player is said to have the potential to sound better than the equivalent from a standard DVD player - presumably because the encoders in the HD DVD players are themselves operating at higher data rates than those used for DVD. (Dolby says the Dolby Digital output from an HD DVD player will be 640 kilobits/second, for example, as opposed to the 448 or 384 kbps available from standard DVDs.) I do know that, in our system, listening to the Yamaha receiver on Revel Concerta speakers, I much preferred the HD DVD's DTS downmix to the standard Dolby Digital soundtracks on the standard DVD versions of the movies I watched. But I can't say how much of the HD DVDs' fuller, less edgy sound was attributable to the encoding as opposed to differences in the mix.
Also, about those limitations I mentioned above: Because of the HD-XA1's early release, or perhaps Toshiba's decision to opt for DTS re-encoding rather than Dolby Digital, the HD-XA1 will not pass a multichannel Dolby TrueHD signal or decode such a signal through its internal processor for output via its multichannel analog output. It will decode or pass two channels of TrueHD, but no more. The manual says the HD-XA1 will decode or pass multichannel DTS-HD, though only up to 5.1 channels. Unfortunately, I was not able to test this function since none of the initial discs carried such a soundtrack; all used Dolby Digital Plus for multichannel sound.