The introduction of Blu-ray has brought about new standards in digital audio that are unlikely to be bettered.
In addition to the PCM, Dolby Digital and DTS available from DVD, we now have four new formats. I am going to ignore two of them – Dolby Digital Plus and DTS-HD High Resolution – for the simple reason that they have been rarely, if ever, used on Blu-ray (although Dolby Digital Plus was a popular choice for HD DVD).
The other two – Dolby TrueHD and DTS-HD High Resolution – are the ultimate in sound carriage systems. They support up to 7.1 channels and are ‘lossless’, which means the original PCM sound is fully reconstituted with no diminution of quality.
They also support sampling rates up to 192,000Hz, giving an upper frequency response of more than 90,000Hz and resolutions up to 24 bits, resulting in a theoretical dynamic range of more than 140dB. There is no point in improving on those figures.
Most new high-quality home theatre receivers incorporate decoders for these new sound systems. Version 1.3 of the HDMI specification allows them to be carried in their original bitstream form.
HDMI is necessary for this because, on Blu-ray, Dolby TrueHD can potentially demand up to 18Mbps, and DTS-HD Master Audio can require up to 24.5Mbps. There is no way S/PDIF connections could be relied on for this.
But some Blu-ray players have decoders for one or both of these audio formats. Dolby TrueHD decoding is fairly common, and DTS-HD Master Audio decoding is rare in Blu-ray players.
So it would seem that the obvious way of delivering the sound would be what we do with DVDs: the player is responsible for extracting the bitstream audio from the disc and sending it to the receiver, which decodes it.
Unfortunately there is a problem with this, and it goes under the name of BonusView.
There are three Blu-ray formats. The originally intended one couldn’t be implemented in time to stave off the HD DVD challenge, so the first version – or profile – was called Grace Period.
The originally intended one came to be called BonusView. This added several capabilities, including picture-in-picture (PIP). With that comes sound-in-sound.
The idea is that the sound from the director’s commentary, running in a PIP window, could be mixed in with the soundtrack sound. So you can still have the Czech soundtrack running for the main movie while the director’s commentary is going.
(There is a third type of sound on Blu-ray as well, called effects sound – which is associated with key presses on the remote control and so forth – and this also needs to be mixed in.)
Consider, for example, the Blu-ray of Starship Troopers 3: Marauder. This disc has the audio in five languages – the English version is Dolby TrueHD 5.1 and the other four are Dolby Digital 5.1. It also has a BonusView PIP commentary feature and the sound in this is DTS-HD in two channels.
Let’s say you choose the English soundtrack. Clearly you can’t pipe both of these down the HDMI connection at the same time. Neither can you just mix compressed audio in the same way as with analogue sound (or, with some limitations, PCM digital sound). They have to be decoded first to PCM, and then mixed together.
Then they are sent down the HDMI cable as multi-channel PCM.
There is only one Blu-ray player on the Australian market at the moment that has the ability to decode all four of the new digital audio formats. The main problem has been DTS-HD Master Audio, which most players cannot decode.
Those that can’t do this still produce listenable multi-channel sound. On Blu-ray, Dolby TrueHD and DTS-HD Master Audio have embedded in them a so-called ‘core’ of, respectively, standard Dolby Digital and DTS sound.
So a player lacking the necessary decoder can still decode multi-channel sound, it’s just that it will be drawn from a lower standard.
So far I have played with five BonusView-capable Blu-ray players. They offer several ways of dealing with audio handling on BonusView discs.
The first two are the Panasonic DMP-BD30 and the Panasonic DMR-BW500. They both operate in the same way when it comes to BonusView disc handling. Neither has decoders for any of the new audio formats, although they do for standard Dolby Digital and DTS.
If you want the highest-quality sound from these players with, say, Dolby TrueHD, then you have to set them to ‘bitstream’ output in their set-up menus for the new audio formats. But that stops them from delivering the secondary (and effects) audio.
Alternatively, you can set the output to convert everything to PCM, but in this case the player will be decoding, say, standard Dolby Digital from the main audio, not the higher-quality Dolby TrueHD. But at least you will be getting both primary and secondary sound.
These players also allow decoding of the ‘core’ audio and mixing then re-encoding to Dolby Digital 5.1, which is useful for those who lack a HDMI input on their home theatre receiver.
The third BonusView-capable player is the low-cost Olin OBDP-1000. This unit is also capable of delivering the audio as a bitstream via HDMI to be decoded by the home theatre receiver, but only the primary audio.
It one-ups the Panasonic units by including real Dolby TrueHD decoding, but not DTS-HD Master Audio.
So, on that Starship Troopers 3 disc, it ought to be able to use the full high-quality Dolby TrueHD audio in converting to PCM prior to mixing with the secondary audio.
‘Ought’ gives me some wriggle room. I know for a fact that the Olin unit can decode high specification Dolby TrueHD sound because I could test a disc with 96kHz Dolby TrueHD 7.1 channel sound, and this arrived at the home theatre receiver as 7.1 channel 96kHz PCM.
But I have no test discs that offer high-specification Dolby TrueHD with secondary audio available, so for all I know the unit is actually decoding the standard Dolby Digital core when called upon to deal with secondary audio as well.
This also has a nifty feature for those who need to rely on an optical or coaxial digital audio connection: it can re-encode the mixed primary and second audio back to full bitrate (1,536kbps) DTS prior to piping it out to a receiver.
The fourth BonusView player arrived on my desk after I had written the first draft of this piece, on the morning of deadline.
The Samsung BD-P1500 is not only BonusView capable but is also claimed to be BD Live ‘ready’, which means that it will access web-enabled content when a suitable firmware upgrade is made available.
For audio handling, it includes a Dolby TrueHD decoder but not a DTS-HD Master Audio one, so in many ways its audio handling is similar to the Olin.
It also offers bitstream output (with no secondary audio, of course), PCM output (the lower-quality DTS core is used for any DTS-HD material) and what it calls Bitstream (Re-encode), which turns the multi-channel PCM mix into standard DTS which can be delivered over its optical digital audio output.
The final contender is the only player at the moment that can deliver the full original audio quality while making use of the BonusView features on a disc. That player is, of course, the Sony Playstation 3.
This unit is incapable of delivering any of the new audio formats as bitstreams. But, since the version 2.30 system update, it can decode all the different audio formats, including DTS-HD Master Audio (which is what that update added), to multi-channel PCM.
Furthermore, it has enough processing power to decode two at the same time and mix them together into the appropriate number of multiple channels.
In other words, only the Sony Playstation 3 can, at this time, deliver the fullest audio quality from all Blu-ray discs in all modes of operation. In addition, it is the only player that currently supports the BD-Live Internet capability … but that’s another story.
Pioneer will soon release its BDP-LX71 player. Initially it will lack DTS-HD Master Audio decoding, but Pioneer says a firmware upgrade will provide that early next year.
But how this unit deals with the intricacies of choosing decoding, bitstream and PIP audio output remains to be seen.Stephen Dawson