Peering Into the Crystal Ball of Digital Audio
As published in The Absolute Sound, issue 113, July/August 1998
by Charles Hansen
When it rains, it pours. Six months ago, there were no high-resolution digital audio
formats available to audiophiles. Today, not only is one available (audio disks using the
DVD-Video format), there are two more on the horizon, DVD-Audio and the Super Audio CD
(SACD) proposal from Sony and Philips using Direct Stream Digital (DSD) technology. The
question naturally arises as to how these three formats differ, and to what degree are
they compatible? And the next question is whether these three formats can peacefully
coexist, or will there be a "format war"? Good questions, to be sure. Of course
we can't predict the future, but the overall picture becomes a "bit" clearer day
by day.
DVD
First, let's look at DVD. The DVD format is specified and controlled by the DVD Forum,
a consortium of over 160 hardware, software, and integrated circuit manufacturers.1
The DVD-Video format was finalized in December 1996, and included a provision for Linear
Pulse Code Modulation (LPCM) audio, including two channels of 96 kHz sampling with 24-bit
resolution (96/24).
The tasks of extending the DVD format are delegated to sub-committees, the primary ones
of interest to audiophiles being Working Group 4 (WG-4) being responsible for the
DVD-Audio specification and Working Group 9 (WG-9) being responsible for copy protection
issues.
The folks behind DVD envision a world where a DVD drive becomes ubiquitous, appearing
in just about every place in your life that you have electronics. In your car, a DVD drive
could not only provide high-resolution digital surround sound, but also a navigation
system by using mapping software in conjunction with a GPS (global positioning system),
plus the ability to play movies for the kids in the back seat. In your computer, a
recordable DVD (DVD-RAM) would allow the storage of massive amounts of data and desktop
video publishing, as well as movie playback and hyper-realistic games. By comparison, what
we audiophiles are seeking, musically satisfying digital audio, would seem to lack
marketing pizzazz.
Audio on DVD-Video
The current crop of DVD-Video based disks from Classic, Chesky, Cardas, and others
offer two channels of 96/24 audio. These will play on any DVD-Video player (the only type
of DVD players presently available), since high-resolution LPCM has been part of the
DVD-Video standard from the get-go.
Of course, the raison d'ˆtre of these disks is their superior sound quality, so
while all DVD-Video player will play these disks you will not experience the full
potential of the format on a mass-market machine. Many of the earlier DVD players
downsampled the 96-kHz information to 48-kHz, losing much of the potential sonic benefit
of the new software. And all of them have less than state-of-the-art power supplies,
analog circuitry, DAC chips, digital filters, et cetera. So while the openness,
transparency, and dynamics of 96/24 can be heard even on a low-cost DVD player, the
audiophile will seek out a true High-End machine to enjoy the music on these disks.
DVD-Audio
If DVD-Video offers high resolution digital audio, why do we need DVD-Audio? There are
two main advantages that DVD-Audio offers; extended capabilities and lower cost.
The maximum data rate for the audio portion of DVD-Video is 6.144 Mbit/second, while a
pure audio DVD-Audio disk is unburdened by video and capable of up to 9.22 Mbit/second.2
This higher data rate will allow for more of what is already available from DVD-Video.
For example, the maximum two-channel resolution will be pushed from 96/24 to 192/24.
Please note that we probably won't see the latter for several more years due to the
general unavailability of the necessary integrated circuits that will perform at that
higher speed. Even then, the 192 kHz capability may be limited to professional or
semi-professional models, and software availability may be limited.
On the multi-channel side, the maximum resolution a six-channel disk will be increased
from six channels of 48/24 to three channels of 96/24 plus either three channels of 48/16
or two channels of 48/24. This would add to the realism attainable from a multi-channel
disk, although many observers are unclear on the best way to meaningfully utilize multiple
channels.
Now increased resolution is fine and dandy, but to avoid obsolescence, compatibility
becomes a key issue. In addition, any format must avoid confusing the consumer if it is to
succeed in the marketplace. The big question is what will happen if you put a DVD-Video
disk into a DVD-Audio player and vice-versa?3
Now, the consumer electronics giants who are in charge of the DVD specification didn't
get to be that size by making poor marketing decisions. And with a world-wide installed
DVD-Video player base of over 1,000,000 units and an installed DVD-Audio player base of
exactly zero units, you can bet that there will be a high degree of compatibility between
these two formats when DVD-Audio disks are released.4
At this point it is seems unlikely that a DVD-Audio player will be able to play the
soundtrack of a DVD-Video movie. However, from all indications most DVD-Audio disks will
play just fine in a DVD-Video player (with a few limitations). In general there will only
be two channels available in a video player, and the sampling rate will be limited to 96
kHz (48 kHz in older machines) by the player itself.
DVD-Video and DVD-Audio Compatibility
Let's examine the issues that determine compatibility of the DVD formats. All DVD disks
have a directory structure that is comparable to that found on a personal computer drive.
There is a "root" directory and two sub-directories, the video title set
(Video_TS) and the audio title set (Audio_TS).
A DVD-Video player is designed to read data only from the Video_TS, which is where a
DVD-Video disk contains both video and audio data. On the other hand, a DVD-Audio player
will normally read data directly from the Audio_TS. This dual directory structure presents
a potential problem if compatibility is to be maintained between video and audio formats.
To overcome this issue, apparently the audio data of a DVD-Audio disk will actually be
stored in the Video_TS directory where it will be available to DVD-Video players. This
will give the backwards compatibility needed for the yet-to-be-released DVD-Audio disks to
play in the large installed base of DVD-Video players. To enable a DVD-Audio player to
access this data in the Video_TS, the Audio_TS will contain navigation pointers to the
Video_TS.
In the most likely scenario, the Audio_TS will only contain data when the maximum data
rate requirement exceeds 6.144 Mbit/second. This would only occur for 192/24 data or
high-density surround sound. DVD-Audio disks like this would not play in a DVD-Video
player. To maintain compatibility with DVD-Video players, one strong possibility is that
the 192/24 data in the Audio_TS will be on one side of the disk, while other side would
contain 96/24 data in the Video_TS.5
Among the major software companies, the strongest supporter of DVD-Audio is the Warner
Music Group. Warner intends to market the DVD-Audio disk as an upscale product to
technically sophisticated buyers. They are not targeting the audiophile. The strongest
selling point will be multiple channels, although 96/24 will be thrown in as an additional
marketing carrot. Expect a street price around the $20 range, at least in the beginning.
Since no DVD disk will play on a CD player, retailers will have to offer a dual
inventory of titles (for the time being). Looking back at the transition from mono LPs to
stereo LPs, or from LP to CD, one can see that it takes perhaps 10 years before the older
format is displaced and is no longer offered.
A DVD World?
Speeding the transition from CD to DVD may actually be the primary motivation behind
the introduction of the DVD-Audio format. By leaving out the video capabilities, a
significant reduction can be made in the price of hardware. It appears likely that
DVD-Audio players will be available for under $200 by the end of next year. This small
price differential over CD players, combined with backwards compatibility with CD
software, should push CD hardware sales to the point of extinction, even in the areas of
car audio and portables. The DVD drive may truly become ubiquitous. Once the hardware base
is installed, the software will follow. In less than 10 years, CD software could go the
way of the mono LP.
By the end of this year, we should start seeing hardware for DVD-Audio from some of the
major manufacturers (Pioneer, Toshiba, JVC, Samsung, and others). Combined with 1999
projected sales of 4,500,000 DVD-Video players and 45,000,000 DVD-ROM equipped computers,
the future looks solid for DVD.
Format Wars?
Perhaps a longer shot, though certainly not to be ignored is DSD, or Direct Stream
Digital from powerhouses Sony and Philips. This format uses delta modulation, in contrast
to the pulse-code modulation employed for CD and DVD. Its makers claim superior fidelity
over LPCM schemes, even those utilizing ultra-high sampling rates. However, it's not quite
clear what to make of this attempt at another high-resolution digital audio standard. Just
about every aspect of this format seems to be filled with contradictions. To wit:
1) Sony has a mixed track record with format introductions. Everyone points out
Betamax, the jury is still out on Mini-Disk, and those of you with good memory can still
recall the Elcaset (!), a stupendous flop. On the other hand, the Compact Disk was a
spectacular home run.6
2) The SACD promises backwards compatibility with existing CD players, a very strong
selling point. Consumers could play the same disk in their DSD-based home system and in
their CD-based car stereo. Retailers would only need to stock a single inventory of disks.
However, such a hybrid disk with two layers would cost at least a dollar more to
manufacture than a standard CD.
Consumers are unlikely to accept a price increase for improved performance that is
unusable on existing hardware. Therefore, the additional cost would need to be absorbed by
the software companies for a single-inventory disk to succeed. With the possible
exceptions of Sony-owned Columbia and Sony Classics, software makers have no obvious
incentive to increase their manufacturing costs.7 In addition,
this dual-layer technology is not exclusive to DSD and could be used for DVD disks as
well.
3) Downsampling an LPCM master tape recorded at a multiple of 48 kHz to 44.1 kHz for CD
release without audible degradation is not a trivial task. In contrast, DSD's high
sampling frequency (2.8224 MHz) allows for easy decimation (down conversion) to any
existing playback standard as well as unforeseen future formats. However, it is not clear
that future formats beyond 192/24 will be necessary or even desirable.
4) Sony plans on a Super Audio CD launch date of early 1999, roughly the same time
frame as DVD-Audio. Surprisingly, this early launch is only being planned for Japan. The
introduction schedule for the rest of the world has not yet been established. If there is
too great of a lag time, it may become difficult for SACD to catch up with DVD-Audio.
Sony faces several more obstacles if DSD is to catch on. Virtually every recording and
mastering studio in the world is equipped with LPCM equipment. While it isn't cheap to
upgrade to 96/24 capability, the hardware is currently available and the changeover is
straightforward. Conversion to DSD would be a more extensive and expensive proposition.8
Perhaps Sony will sell DSD recording equipment at a loss to induce such a conversion, much
as Pacific Microsonics is currently doing with HDCD. Sony certainly has deep enough
pockets to do this on a large scale.
Another challenge is the difficulty of editing the bitstream of the DSD format.9
Professional digital editing tools such as Sonic Solutions have been developed over the
last 15 years to the point where they have become indispensable parts of the modern
recording process. Sony is currently developing editing tools for DSD, although they will
be playing a catch-up game to compete with LPCM in this arena.
SACD vis-a-vis DVD
The issue of compatibility with DVD is unclear at this point. We know that a SACD disk
will be read by the same basic mechanism as DVD. However, Sony has been even less
forthcoming about technical details on DSD than the DVD Forum has been on DVD-Audio.
We do know that the DVD-Audio standard provides for a wide variety of data streams
including DSD, DTS, Dolby Digital, as well as future unspecified formats. However, such a
DVD-Audio disk would be required to also contain at least two channels of LPCM to ensure
backwards compatibility with DVD players.
At this point, Sony's plan is to pass over this opportunity to merge the two formats,
and establish DSD as a distinct format. Therefore, a DVD player would only be able to read
the low-resolution CD layer when playing an SACD. Similarly, an SACD player presumably
would not have the capability of reading DVD disks.
It may be possible that the DSD signal could be presented at the digital output of a
DVD player, so that adding DSD capability would only require an add-on processor. Or it
may be that the core processing electronics are so different that the only commonality
between the two types of players would be the drive mechanism itself. Given the track
record of the High-End audio industry and the fact that both formats are based on the same
basic drive mechanism, it would not be unreasonable to assume that many of the High-End
DVD players would be able to incorporate an retrofittable path to DSD should that become
desirable.How Does It Sound?
Of course as audiophiles, many of these practical issues are unimportant. What we
really want to know is, "How does DSD sound compared to DVD-Audio?"
The answer is that we don't know yet for certain. The only semi-public comparisons
between the two formats have been conducted by Sony and Philips where DSD was the apparent
victor, although one would hardly expect otherwise.10 The
group with the most exposure to both 96/24 and DSD is the professional recording and
mastering community. Mastering engineers Bob Ludwig and Bernie Grundman have announced
plans to add 96/24 capability to their facilities, while specialty record labels Telarc
and DMP have made a commitment to DSD. Indeed, Tom Jung of DMP is emphatic that DSD offers
a dimensionality that is unavailable from LPCM.
Clearly, both formats are far superior to CD. In fact, it appears that both of them are
good enough that any superiority one of them may offer could be a moot point. Consider
that the High-End industry continues to extract higher and higher sound quality from
16/44.1 CDs. The implication is that even this relatively crude link has been hampered by
the execution of the storage and conversion processes. Indeed, it may be that these new
formats actually offer what the CD proponents have claimed all along _ a link so
transparent that it no longer is the weakest one in a very long chain.
Whether the two formats will merge, peacefully coexist, or foment a format
"war", the possibility of high resolution digital audio has become a reality. So
in a very real sense, the audiophile is the real winner. Regardless of how many formats
survive in the marketplace, a convenient source of true High-End sound is finally at hand.
Bio Note
Charles Hansen designs high performance audio equipment for Ayre Acoustics, Inc., a
member of CEMA's Advanced Audio Disk Working Group. In addition to currently working on
digital audio projects, he enjoys listening to LPs (whose own format issues were resolved
over 30 years ago).
1 The 10 original DVD Forum members hold the patents on this
technology and therefore share in the royalties generated by hardware and software. Over
4000 patents apply to the DVD format, with the percentage breakdown as follows: Matsushita
(Panasonic) _ 25%, Pioneer _ 20%, Sony _ 20%, Toshiba _ 10%, Philips _ 10%, Hitachi, _
10%, Thomson (RCA/GE) _ 5%, JVC, Mitsubishi, and Warner _ negligible. These 10 members
also hold the key decision-making powers. In May 1998, seven additional companies were
added to this decision-making committee.
2 The draft specification of DVD-Audio should be available by the time
you read this, but the final specification isn't due for release until September, so much
of what follows must be regarded as provisional.
3 The information that has been leaking out concerning DVD-Audio has been
somewhat confusing on this point. Most of the confusion stems from the fact that the DVD
Forum wants as little press coverage as possible on DVD-Audio. Their intent is to avoid
pulling down the sales of existing CD players and disks before the new format has been
fully established.
4 If you're skeptical, take a look at the current crop of DVD-Video
players, which largely feature 96/24 digital-to-analog converters (DACs). Those aren't
there for movies, virtually all of which provide compressed Dolby Digital surround sound
rather than LPCM soundtracks. Dolby Digital and DTS movie soundtracks play back at a 48
kHz sampling frequency.
5 There is no additional price penalty to a double-sided DVD disk,
because all DVD disks are made by bonding two 0.6 mm disks back-to-back. Single-sided DVD
disks contain a dummy layer that costs the same to manufacture as an information-bearing
layer.
6 The focus of this discussion will be Sony, as they appear to be the
main motive force behind DSD.
7 Philips sold Polygram to Seagram at the end of May 1998.
8 Large recording studios often have elaborate automated, multi-channel
digital mixing consoles that cost in excess of $1,000,000. These LPCM-based products do
not interface with DSD data. It is ironic that Sony's Pro Audio Division is the maker of
many of these consoles.
9 This is one of the main reasons that DVD-Audio has been widely
supported by the computer industry, including chipmaker giant Intel.
10 Like the old saying in Washington, D.C. says, "Follow the
money." The very real possibility of a format "war" seems to be driven by
two forces _ the DVD group wanting to wrest away the CD hardware and software royalty
stream that Sony and Philips have enjoyed for the last decade-and-a-half, and Sony/Philips
equally anxious to maintain it, although spokespersons for Sony deny that this is the
motivating factor behind DSD.
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