Home Page | About Me | Home Entertainment | Home Entertainment Blog | Politics | Australian Libertarian Society Blog | Disclosures

The New Digital Sound
The promise and complications of high definition digital audio on Blu-ray

This version: 2 December 2008

Originally published in Australian HI-FI in two parts: July/August 2008, v.39#4, pp.32-34, and September/October 2008, v.39#5, pp.48-52

Even before the compact disc was first released on the consumer market, some audiophiles had reservations about digital recording technology. Where the problems, if any, may lay with digital technology is often the subject of vigorous debate. But whatever they may be, the newest consumer formats should eliminate them, potentially providing the most precisely defined sound ever made available in the home.

That new digital sound is available from the new high definition video disc format: Blu-ray. The same sound was also available on HD DVD, Blu-ray's competitor, but that format is gasping its last as I write. So we shall consider Blu-ray only here, and if you happen to have HD DVD, most of this applies equally to that (I will point out the few minor differences between the two).

I chose my words carefully earlier, when I said 'the most precisely defined sound'. When you think about it, the more closely the wiggly electrical line of the signal, as delivered in your home, conforms to that created at the recording studio, the higher the fidelity of the sound.

One way of delivering that electrical line to your home is as a physical impression cut into the surface of a vinyl disc. Unfortunately this groove can sometimes be quite approximate, especially when it has sharp, random inaccuracies, aka clicks and pops.

Many complaints about the sound of CD come down to claims that the format is too large-grained. A CD tracks that electrical wiggle 44,100 times per second, recording its position on a scale 65,000-odd positions tall (that is, 16 bits of resolution). It is possible that, in certain circumstances, the approximations that this imposes on the signal are audible. Of particular concern is when the signal is at a low level, or very high in frequency.

That's where some of Blu-ray's new audio standards can improve things. DVD Audio and, to a lesser extent, SACD also improved things, except that these formats have effectively failed to achieve consumer acceptance, so there is very little program material to enjoy with these.

Flawed But Better

Like DVD, Blu-ray supports two channel PCM (ie. CD-like sound), Dolby Digital and DTS. But it adds five additional sound formats.

Two of these are of some additional value for the audiophile. These are Dolby Digital Plus and DTS-HD High Resolution.

Dolby Digital Plus builds upon Dolby Digital, and DTS-HD High Resolution builds upon DTS, but both remain lossy formats. That is, like MP3, they employ psycho-acoustic principles to completely eliminate some elements of the sound on the theory that you can't hear those elements anyway (they are supposed to have been masked by other sounds). To a large extent we can accept that those principles are correct, and they provide listenable results in many circumstances, and for some material. Of course, for the very best listening we would like to avoid lossy compression formats entirely, which we shall get to shortly.

The amount of sound lost -- and the audibility of those losses -- depends upon the quality of the algorithms used, and the proportion of the sound data that is thrown away. Algorithm quality is something not easily decided upon, but the amount of data thrown away is easily deduced from the 'bit rate' of the digital audio signal.

With DVD, Dolby Digital was limited to a maximum of 5.1 channels (6.1 using a matrixed centre rear) and 448kbps (kilobits per second). For about half of Dolby Digital 5.1 discs, the bitrate was actually 384kbps. For 5.1 channels of uncompressed digital sound with 16 bits of resolution and 48kHz sampling, the required bitrate is 4,608kbps. So on DVD, Dolby Digital uses a 10.3:1 compression ratio (or greater: 12:1 for the lower bitrate variant). Most of that ninety-odd per cent of space savings comes from sound that is simply thrown away.

On Blu-ray, though, even standard Dolby Digital gets a boost: 640kbps is the maximum allowed (with HD DVD, the limit remains 448kbps). In practice, the majority of the 60-odd Blu-ray titles that I've checked which have standard Dolby Digital sound enjoy the higher 640kbps data flow.

Dolby Digital Plus adds to this the capability of a bitrate of up to 1,700kbps (3,000kbps on HD DVD), ensuring even less data is thrown away. DD+ also enjoys support for up to 7.1 discrete channels and, of course, adds another decade of development in the art of compression, so it ought to deliver much better sound than Dolby Digital.

Except that it isn't used. Of the 150-odd Blu-ray titles that I've checked, only one has Dolby Digital Plus sound. And that title is Dolby Laboratories' own demonstration Blu-ray disc: 'The Sound of High Definition'. DD+ was very popular for HD DVD because it was a 'mandatory standard' for HD DVD. That is, all HD DVD players were required to have decoders built in for DD+. However it wasn't a mandatory standard for Blu-ray. The film companies which adopted Blu-ray looked elsewhere for their audio standards.

Standard DTS does not get the same kind of de facto Blu-ray boost in bitrate. On DVD, DTS 5.1 (and 6.1 ES Discrete and 6.1 ES Matrix) comes in two flavours: 768kbps and 1,536kbps. The latter is what is used in DTS-enabled cinemas and on a few rare DVDs. But most DTS DVDs receive the half-rate 768kbps (including 'Superbit' discs).

Remember, the higher the bitrate used in a lossy compression system, the less the source is compromised.

Not many Blu-ray discs receive plain DTS sound tracks, and those that do usually receive this for foreign language dubs to save space. Of the four or five I have checked, all but one received the 768kbps treatment.

However DTS-HD High Resolution bumps this up even further. On Blu-ray, DTS-HD High Resolution can use bitrates of up to 6,000kbps (3,000kbps on HD DVD) and it also supports 7.1 discrete channels. But, as I write, it is used rarely on HD DVD, and not at all on Blu-ray. Yes, I have not one Blu-ray title with a DTS-HD High Resolution sound track -- and in that I include the DTS 2008 High Definition demonstration Blu-ray!

Whatever its merits, it seems likely that DTS-HD High Resolution is a dead format.

Potential Perfection

What is used quite extensively in Blu-ray are the three formats that can deliver the best sound of all.

These formats are called Dolby TrueHD, DTS-HD Master Audio and ... LPCM. Yes, linear pulse code modulation -- the same standard introduced to the consumer nearly a quarter of a century ago to the consumer -- lives on!

Improved, though.

On a CD, as mentioned above, you get two channels (CD is actually specified for four channels, but I don't think any four channel players or discs were ever released) with 16 bits of resolution, providing 65,000-odd values for storing signal level, sampled 44,100 times per second.

With DVD Video, this was kept at two channels, but the resolution was bumped up to a maximum of 24 bits (16.7 million levels) and 96,000 hertz sampling.

Blu-ray simply sneers at that.

It can deliver up to 7.1 channels of LPCM at up to 96,000 hertz and 24 bits, or up to 5.1 channels at 192,000 hertz and 24 bits! (With HD DVD, 192,00 sampling cuts the capacity of LPCM back to two channels.)

These figures both produce enormously greater resolution of the sound. For instance, while 44.1kHz barely gives you an upper frequency response (after the necessary filtering) of 20,000 hertz, 48kHz sampling manages to deliver a little over 20kHz, 96kHz sampling easily provides 40,000 hertz high frequency extension, and 192kHz gives you an upper frequency of 90,000+ hertz.

And unlike the DSD system used on SACD, these high frequencies aren't buried under steaming piles of ultrasonic noise, but are delivered as purely as if they were in the blandest of the midrange areas of human hearing.

But note my careful use of words: 'can deliver', 'up to' and so on.

The LPCM supported by Blu-ray is potentially very powerful, but it all depends on the source. And, as I write, there is no material that uses or even approaches these capabilities.

Because support of the other new digital audio standards was limited in early Blu-ray players, quite a few discs were released with multichannel LPCM sound. In fact, I have 26 of these discs in my possession. Of these, all use 48kHz sampling, all deliver 5.1 rather than 7.1 channels, and all but two use 16 bits of resolution.

The two exceptions -- Apocalypto and Chicago (the latter purchased from the US) -- have 24 bit sound.

So, for the most part, the resolution as formally defined by the sampling frequency and number of bits used to capture the sound, hasn't increased for most of these discs over the Dolby Digital versions (Dolby Digital routinely uses 48kHz/16 bits). But the lossy compression has been eliminated, so there is no intentional elimination of actual program content.

The two remaining audio standards? This is where the Blu-ray game really comes into its own. Or it should. These are Dolby TrueHD and DTS-HD Master Audio.

Both of these are very similar. Both are lossless compression systems, somewhat like the Meridian Lossless Packing used in DVD Audio (very similar indeed in the case of Dolby TrueHD, since it is largely built upon MLP). Both extend the potential capability of the sound to a full 7.1 channels at a full 24 bits of resolution and a full 192,000 hertz sampling rate. Such sound, should it ever appear on a Blu-ray disc, must without a doubt must be the most precisely defined sound ever delivered into the home because the granularity with which it is defined is the finest ever.

What both these lossless compression systems do is simply pack LPCM into a slightly smaller space. Their compression algorithms can typically provide about a 2:1 compression ratio. In the case of Dolby TrueHD, the system in fact improves on LPCM in providing improved error checking and data reconstruction in the event of data loss. I wouldn't be surprised if this was also the case for DTS-HD Master Audio (whatever possessed DTS to come up with names guaranteed to be confused -- DTS-HD Master Audio and DTS-HD High Resolution -- for two significantly different systems?)

Some critics have suggested that DTS-HD Master Audio must be 'better' than Dolby TrueHD, at least on Blu-ray, because the former can run at up to 24,500kbps, whereas Dolby TrueHD can manage 'only' 18,000kbps (both are limited to the lower figure on HD DVD). In reality, full 192kHz, 24 bit, 7.1 channel material delivered in LPCM format would require 36,864kbps. It would be very rare indeed for some material to be unable to be packed into Dolby TrueHD's 18,000. If worse comes to worse, the sampling frequency of the 0.1 channel can be chopped down to, say, 32,000 hertz since it is only intended to carry up to 120 hertz.

Both of these systems have already been extensively used on a wide range of Blu-ray discs. However, once again, their full capability has simply not been used. Most (the exceptions being demo discs) provide 5.1 channels and 48kHz and 16 bits, packed into a smaller space.

Obviously this is once again a marked improvement over DVD. More importantly, though, is that it offers a path to the highest of high fidelity sound delivery systems ever.

I am an optimist. As the world increasingly becomes a place where the normal channels for distributing music becomes via the Internet in some lossily compressed MP3-like format, the market will provide for those demanding unsullied purity in their music.

The Blu-ray format provides this channel. When the recordings are made with 7.1 channels, 24 bits of resolution, and 192,000 sampling providing over 90,000 hertz of bandwidth, Blu-ray will allow this to come into your home.

It isn't only for movies.

Getting it out of your player

(Part 2 of The New Digital Sound)

In the last issue I detailed the new audio standards available from Blu-ray and HD DVD. But as I indicated, having those new audio standards on a Blu-ray disc does not necessarily mean that you can enjoy their full quality. To do that you need the right equipment and the right connections.

When I talk about 'right equipment', I am talking about equipment technically able to deliver the goods. Whether that equipment does it well or not is another matter, of course, and will depend upon the quality of the equipment.

Also, remember that the potential quality of sound is constrained by the source. For example I have in my disc collection an HD DVD of The Adventures of Robin Hood, the 1938 Errol Flynn swashbuckler. There is no need to use, say, Dolby TrueHD or DTS-HD Master Audio on such a movie because, let's face it, the recording quality was crap back then. As it is, Warner Brothers has used Dolby Digital Plus for the encode (in three different languages, plus the commentary). Warner Bros seems to have cleaned the sound, leaving only a little hiss in the mix. But since it is mono, and the bandwidth limitations are quite extreme, they have managed to get away with using a bitrate of only 64kbps for each of the audio tracks! (The main audio encode in Dolby Digital Plus is commonly 1,536kbps.) This disc sounds about what you would expect for a 1938 sound track, and if the low bitrate used for the lossy compression makes things worse, it's beyond my ability to detect.

By contrast, the HD DVD release of Season One of the original 'Star Trek' sees the sound, which was recorded for mono playback way back in 1965/6, remixed to Dolby TrueHD 5.1. It sounds adequate, but not high in fidelity.

In general, movies made in the 1990s and on are going to sound better than earlier ones, thanks to the use of digital recording technology. Excellent results are available for some movies from the 1970s, and some from the 1960s are decent. It largely depends on whether the original elements were captured on multitrack magnetic tape, and whether they survived for clean-up and reassembly.

A Recap

When DVDs were released there were four broad categories of sound available: PCM, Dolby Digital, MPEG2 and DTS. For Australia and Europe, PCM, Dolby Digital and MPEG2 were the 'required' standards (MPEG2 wasn't one for the US). MPEG2 audio was only used for a small number of DVDs in the early days. DTS could be present on DVDs, but only if accompanied by one of the required standards.

Since then improved versions of PCM, Dolby Digital and DTS have been developed, and included on Blu-ray. PCM has grown from DVD's two channels to up to 7.1 channels and up to 24 bits and 192kHz sampling. Dolby has spun off its higher bitrate, but still lossy, version, called Dolby Digital Plus, and a new 'losslessly compressed' version, derived from the Meridian Lossless Packing system on DVD Audio, called Dolby TrueHD. DTS, likewise, has a higher bitrate lossy version called DTS-HD High Resolution, and a losslessly compressed version called DTS-HD Master Audio. MPEG2 has disappeared as a sound standard. In addition to these, Blu-ray also supports the legacy sound standards of Dolby Digital and DTS.

The newer formats support up to 7.1 channels. The various wrinkles on all of these are shown in the table. Lossless compression systems allow the original PCM sound to be fully reconstituted with no diminution of quality. Lossy systems remove the part of the sound content that is supposed to be inaudible anyway, but of course there are always doubts about that.

With the loss of HD DVD, it looks as though the Blu-ray industry is settling on standard Dolby Digital and DTS as the lossy formats, and multichannel PCM, DTS-HD Master Audio and Dolby TrueHD as the lossless ones. I note that the first few titles announced by the last major hold-out against Blu-ray -- Universal Studios -- are featuring DTS-HD Master Audio sound, whereas in their previous HD DVD incarnations they carried Dolby Digital Plus.

Digital FormatLossyChannels1DVDBlu-rayHD DVD
MandatoryMax bitrateMandatoryMax bitrateMandatoryMax bitrate
Stereo PCMNo2.0Yes4.6Mbps2N/A7N/AN/A7N/A
Multi-channel PCMNo2.0-7.14, 5--Yes27.7MbpsYes18.4Mbps
Dolby DigitalYes1.0-5.1Yes0.448MbpsYes0.64MbpsYes0.448Mbps
Dolby Digital PlusYes1.0-7.1--No1.7Mbps6Yes3Mbps
DTS-HD High ResolutionYes1.0-7.1--No6MbpsYes3Mbps
Dolby TrueHDNo1.0-7.1--No18MbpsNo18Mbps
DTS-HD Master AudioNo1.0-7.1--No24.5MbpsNo18Mbps
1. Discrete channels, both Dolby Digital and DTS on DVD have enhanced versions in which a sixth channel is matrixed into the two surround channels
2. At 96kHz, 24 bits resolution
3. On DVD the most common DTS bitrate is 0.77Mbps
4. Blu-ray: for sampling rates up to 96kHz. For 192kHz the maximum number of channels is 5.1
5. HD DVD: for sampling rates up to 96kHz. For 192kHz the maximum number of channels is 2.0
6. Up to 4.736Mbps should provision be made for more channels in the future (the Dolby Digital Plus specification supports up to 13.1 channels)
7. These are treated as just one type of Multi-channel PCM

Getting At The Sound

Now you'd think enjoying these new sound formats would be easy. All these sound standards could simply be decoded and produce glorious sound from your speakers. Especially movies using one of the three lossless sound standards: Linear PCM, Dolby TrueHD and DTS-HD Master Audio.

But that requires the sound to be decoded. Should it be decoded in the Blu-ray player, or (like decent DVD-based systems generally do), in the home theatre receiver?

It is tempting to say -- well, let's just do it the same way that it has always been done: bitstream output of the digital audio, in whatever format it is provided on the disc, and let the receiver do the work. Unfortunately, this requires certain capabilities which do not reside in all Blu-ray players, and even for them could come at a cost.

The alternative would be to have the player decode the relevant audio and deliver it to the receiver. But as I write there is only one player capable of doing that ... one that might be a surprise to many readers.*

Bitstream Delivery

So let's say we go with the first option: pipe the bits of sound, pretty much as they appear on the surface of the Blu-ray disc, out to a home theatre receiver and let it do the decoding.

First, the familiar S/PDIF connections -- whether optical or coaxial -- are simply not up to the job. Oh, for sure, they could carry most of the audio most of the time ... had the necessary specifications been made and implemented. But since they weren't capable of carrying of every single possibility, it was pointless to do this. So HDMI is required.

The first few versions of HDMI, though, did not include this capability in their specifications so they won't do the job either. HDMI 1.3 does include this capability. However it is not a compulsory capability, even for HDMI 1.3.

So what did players without HDMI 1.3 do? In general, they gave you two options. The first was internal decoding, wherein the multichannel sound would be decoded to PCM 5.1, 7.1 or whatever. Right from the very start, HDMI was specified to support 7.1 channels of PCM. Otherwise, they could send a bitstream down either S/PDIF or HDMI to the receiver.

Huh? Didn't I just say that you need HDMI 1.3 for the bitstream? Didn't I say that S/PDIF couldn't handle the new audio formats?

Correct, on both counts. The bitstream which is sent is not the same as that sent via HDMI 1.3 (suitably enabled). The new audio standards on Blu-ray were designed with older equipment limitations kept in mind. So buried inside a Dolby Digital Plus bitstream, or a Dolby TrueHD bitstream, is a boring old Dolby Digital bitstream. Likewise, the new improved DTS formats also include within them a standard DTS bitstream. With your Blu-ray player you could select the Dolby TrueHD 48kHz 24 bit audio track, and it would be delivered as standard Dolby Digital via HDMI or S/PDIF. A touch better than DVD-standard Dolby Digital, because that topped out at 448kbps, whereas Blu-ray Dolby Digital supports up to 640kbps. Likewise your DTS-HD variants would be delivered as standard DTS of a variety able to be used by modern home theatre receivers.

You would lose any extra resolution inherent in the original recordings (24 bits, if provided, would be cut down to 16, 96 or 192kHz would be reduced to 48kHz). You would lose the perfection of lossless compression. And if, in the extremely rare case, the sound offered 7.1 channels, the two centre rear channels would lose their discrete nature.

You will find that Samsung Blu-ray players from the BD-P1400 model and on, Panasonic from DMP-BD30 and on, Pioneer from the BDP-LX70A and on, support bitstream output of all the audio standards. Some players, such as the Sony BDP-S500 Blu-ray player are weirdly intermediate, in supporting some, but not all, of these audio standards (in the Sony's case, it will deliver all but DTS-HD Master Audio). The Sony Playstation 3, despite being equipped with HDMI 1.3, will not deliver any of the new audio standards as original bitstreams to your home theatre receiver.

So, at first glance, the obvious solution is to buy a home theatre receiver with full decoding of the new audio standards (there are a number of models around now at reasonable prices), and something like a Panasonic DMP-BD30 Blu-ray player.

If only. Things get a bit more complicated here because the Panasonic DMP-BD30 is that much closer to being a real full-blown Blu-ray player: a BonusView Blu-ray player.

Picture In Picture, Sound In Sound

BonusView Blu-ray players offer features which were always intended to be included in Blu-ray players, but couldn't at the outset because of technological limitations. They were earlier known as players conforming to the 'Final Standard Profile'. All Blu-ray players released after October 2007 must conform this profile.

Bonus View players offer a few extra features with suitably encoded discs. Only one of those is relevant here, but it is a doozy. They support Picture-in-Picture, familiar to many from some of the fancier TVs around. But they also support Sound-in-Sound. These are more formally known as secondary video and secondary sound.

The idea is that a movie may have a special feature which consists of, say, a director's commentary, except that it would be delivered as a picture in the corner of the screen. A number of HD DVDs already have this feature, and some Blu-ray discs with similar kinds of features are just starting to appear.

From an audio point of view, the difference between this kind of commentary (or it could be some other special feature which just pops up from time to time) is that the sound from the secondary video is 'mixed' with the sound from the primary video, it doesn't just replace it. Both the main sound (primary) and the PiP sound (secondary) can be any of the supported formats. For example on the Blu-ray disc of 'Aliens vs. Predator: Requiem', this feature is used within one of the special extras. The background sound is presented in 5.1 channel DTS-HD Master Audio. Whenever any of the video clips are selected within this extra, they are presented with two channel DTS-HD sound (it wasn't clear from the equipment I was using whether it was DTS-HD Master Audio or High Resolution, but I would expect it to be the former).

Clearly you can't pipe both of these down the HDMI connection at the same time. Nor can you just mix together compressed audio in the same manner you can analogue sound (or, with some limitations, PCM digital sound). They have to be decoded first to PCM, and then mixed together. Then they are delivered down the HDMI cable as multichannel PCM.

But here we have yet another problem. There is only one Blu-ray player on the Australian market, as I write, that has the ability to decode all four of the new digital audio formats*. The main problem has been DTS-HD Master Audio. The Pioneer BDP-LX70A, for example, can decode Dolby TrueHD, but not DTS-HD Master Audio. A lot of discs use DTS-HD Master Audio as their main format. All from 20th Century Fox do. The Panasonic DMP-BD30 does not have decoders for any of the new audio standards, although it does for standard Dolby Digital and DTS.

If you want the highest quality sound from these players, then you have to set them to 'bitstream' output for the new audio standards in their setup menus. But that would mean that they couldn't provide the secondary audio.

The only consumer players yet available in Australia which support BonusView discs are from Panasonic. They have a complicated, but fairly effective, approach to solving these problems. I have described this in some detail in the box.

There is, however, one other Blu-ray player that also deals with these things, and does it in the best possible way. That's 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 standards, including DTS-HD Master Audio (which is what that update added), to multichannel PCM. Furthermore, it has sufficient 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 which supports the BD-Live Internet capability ... but that's another story.

* More have become available since I wrote this.

BOX: Audio handling in Panasonic DMP-BD30 and DMR-BW500

Because the Panasonic units lack internal decoders for the high end sound formats, they will only provide the full audio quality of DTS-HD Master Audio and Dolby TrueHD if set to output the audio as a bitstream. There are extensive setup options to handle all this.

Panasonic has provided three 'Priority settings' for this purpose. These are called 'Audio Quality', 'Secondary Audio' and 'User'. The first two have fixed settings for the four subsidiary settings available, while 'User' allows them to be set independently. The first three of these subsidiary settings are 'Dolby D/Dolby D +/Dolby TrueHD', 'DTS/HTS-HD', 'MPEG Audio', each of which can be switched to either PCM or bitstream (in the 'User' setting, anyway). The fourth is 'BD-Video Secondary Audio', which can (in the 'User' setting) be switched to 'On' or 'Off'.

In the case of 'Audio Quality', Secondary Audio is switched off, and all the output settings are 'Bitstream'. For 'Secondary Audio', as you would expect, Secondary Audio is switched on, but all the output settings are 'PCM'.

If you have the player set to 'Secondary Audio' and are playing BonusView material, the two audio streams are extracted, decoded to PCM, mixed and output as PCM. However you are getting the (slightly) lower quality DTS version (or Dolby Digital), rather than the ultrahifi DTS-HD Master Audio (or Dolby TrueHD) version. If you have the player set to 'Audio Quality', the primary audio is delivered as a bitstream, and you don't hear the secondary audio at all. You get the secondary video (ie. the PiP), but not the sound that goes with it.

You can also select the 'User' setting, switch on Secondary Audio, but leave the various standards set to 'Bitstream'. This then works the same way as the 'Secondary Audio' setting -- the two streams are extracted, decoded to PCM and mixed -- but with one extra step. In this case, the player re-encodes them on the fly to Dolby Digital 5.1. This allows older home theatre receivers which rely on an optical or digital audio connection to be supported. Clever!

© 2008 by Stephen Dawson