IT IS 1999, just two years away, and the family has a new toy. A new-style
hi-fi system with half a dozen speakers round the room and up the walls. The
speakers are unobtrusive flat panels disguised as paintings and photographs. The
disc in the player looks like a CD yet reproduces music with a faithfulness that
is far superior to anything around today. The sound spreads not only round the
room but also up and down, reproducing the acoustics of a concert hall, the
physical height of a church organ and the stage positioning of Gounod鈥檚 opera
Romeo and Juliet.
To smooth the transition to this new aural sensation, manufacturers have
created a hybrid disc with two recordings on it鈥攖he super-quality version
and an old-style stereo rendition. This way people with CD players can buy the
new discs and listen to them as though they are conventional CDs. When they
learn that so much extra quality is locked inside their new discs, they will be
tempted to upgrade their hi-fis. Electronics and recording companies hope this
ploy will spark a virtuous circle of disc and player sales.
The new super audio disc relies on the high-density optical recording
technology developed for the Digital Video Disc, which is just going on sale as
a medium for Hollywood movies. A single DVD can carry as much information as six
or more ordinary CDs, and the new DVD-Audio format will use all this for sound,
perhaps with still pictures of the performers.
Advertisement
It all sounds too good to be true, and perhaps it is, because DVD-Audio is
proving to be a focal point for a global mess of technical, commercial and
political squabbles. All the big electronics companies have their own ideas
about the best recording technology, and are vying to make their own systems the
world standard. Record companies say that DVD-Audio must sound obviously better
than CD recordings, even to an untutored listener. At the same time they insist
that the new discs must play on today鈥檚 equipment, and they want technology to
be built into the new systems that will prevent people copying their music. And
all this at a price that will not turn people away from record shops.
Stranglehold
The CD we play today was invented by Sony and Philips, and even now the
Japanese and Dutch companies collect a royalty on every player and disc sold.
Other electronics companies, particularly in Japan, have long resented this
stranglehold and resolved to have a share in any future disc
technology鈥攁udio or video. The resulting battle between companies over
high-density video disc systems led ultimately to the squabbles we now see over
DVD-Audio.
In the early 1990s, the Japanese electronics companies Toshiba and Panasonic
and the American media conglomerate Time Warner developed a high-density digital
video disc system they called SD, for Super Density. Independently, Philips and
Sony developed the similar but incompatible Multimedia CD. In December 1995, the
rival teams sensibly buried their differences and agreed a single standard,
which they called the Digital Video Disc. One 12-centimetre DVD鈥攖he same
size as the familiar CD鈥攃an store a complete feature-length movie with
better-quality pictures and sound than you get from broadcast TV.
Since then, only the acronym has stayed the same. The DVD consortium has
acquired five new members: Hitachi, JVC, Mitsubishi, Pioneer and Thomson. And on
top of this, the name of the format has changed to Digital Versatile Disc to
embrace a ROM version for computers. One DVD-ROM can store between 4.7 and 17
gigabytes of data, compared to the CD鈥檚 650 megabytes.
But this capacity, huge as it appears, is still not enough. Accommodating
every frame of a feature-length movie on a DVD soaks up so much space that it
puts the squeeze on the soundtrack. In modern films, speech, music and sound
effects are usually delivered by at least five channels, to give the audience
the sensation of surround sound. The standard for DVD-Video sets aside a mere
384 kilobits of data per second to carry all this sound. By comparison, a
conventional CD has 1.4 megabits per second for its two channels of stereo
sound. So DVD-Video needs heavy data compression to squeeze the sound in
alongside the pictures. How this should be done is still hotly contested.
The clear leaders are Dolby Digital AC-3, developed by Dolby Laboratories of
San Francisco, and MPEG-2 audio, developed in Europe for digital TV and radio.
The problem with both of these is that they are 鈥渓ossy鈥�: the compression process
discards less important information, such as quiet sounds that are masked by
louder sounds of similar frequency. The assumption is that listeners will not
notice the difference鈥攁nd most don鈥檛. But this is not good enough for the
discerning ears of hi-fi buffs, who are alarmed at the prospect of a technically
inferior standard becoming established for audio recordings.
The first warning shots on compression were fired five years ago, when an
international hi-fi industry group called the Acoustic Renaissance for Audio
(ARA) heard that the video industry was developing high-density discs. It warned
that lossy compression would limit the disc鈥檚 potential as a high-quality audio
medium. 鈥淚f we鈥檇 done nothing there was a risk that a new generation would grow
up thinking that music is video with compressed sound,鈥� says one of the ARA鈥檚
founders, Bob Stuart of British hi-fi company Meridian.
The ARA also wanted to promote surround sound with height to create the
illusion of a natural sound sphere. To deliver this, it recommended using
Ambisonics, a signal processing system invented twenty years ago in Britain but
largely ignored because neither vinyl LPs nor CDs could carry the full signal.
But a high-density disc would be able to accommodate it. It uses three channels
to spread sound horizontally, through 360 degrees, plus a fourth to add
information about height. Ambisonics works best if none of the digital signal
has been lost through compression.
Lossless compression is already widely used in the computer industry, to
squeeze data without losing any of the information it carries. This can be done,
for example, by reducing the number of bits that represent spaces between
written words, and replacing long strings of identical characters with short
codes. No information is thrown away, it is just stored more efficiently.
Hecklers behind you
The ARA recommended that a DVD-audio disc should deliver several channels of
sound, each sampled 96 000 times a second. This would allow it to handle a wider
range of frequencies than a CD, which has a sampling frequency of 44.1 kilohertz
(see Diagrams).
The ARA also called for every sample to be coded with more
bits than on CD, to give a greater volume difference between the quietest and
loudest sounds. At present, CDs encode every sample as a 16-bit digital word;
the ARA called for this to be replaced with a 24-bit word.
Two years ago, ARA representatives went to Tokyo to meet the Japan Audio
Society, a group of hi-fi experts that advises Japanese manufacturers.
Initially, the JAS did not seem very interested in multichannel surround sound.
The visitors from the ARA simply played them a recording of a singer on stage
being heckled by the audience. In surround sound, the hecklers are at the rear
of the room, while in stereo they appear on stage alongside the singer. The JAS
got the message. The society talked to the DVD consortium, which agreed that
there should be a separate standard for the audio version with multichannel
surround sound and lossless compression.
As news leaked out that DVD-Audio was on its way, record companies smelled
loss of consumer confidence in CD and feared that events were getting out of
their control. 鈥淲e do not want to be faced with a fait accompli put
together by the hardware industry,鈥� said Nicholas Garnett, director-general
of the International Federation for the Phonographic Industry (IFPI). In the
middle of last year, the federation helped to set up an international steering
committee (ISC) to put forward the recording industry鈥檚 case and comment on the
plans of the electronics companies.
All the major Japanese electronics companies have developed their own
proposals for DVD-Audio technology. Some follow the line proposed by the ARA:
Pioneer, for example, demonstrated a working 96-kilohertz 24-bit system in
London last year. It used an 8-centimetre disc and carried super-fidelity sound
and accompanying still pictures. The miniature DVD can run for as long as a
conventional CD and plays on shirt-pocket portables. But the ISC has since said
that DVD-Audio should use 12-centimetre discs because that鈥檚 what the public is
used to.
Sony has also developed a system, called Direct Stream Digital, which is
supported by Philips. DSD is a 鈥渂it-stream鈥� system that uses a rapid stream of
single bits instead of fixed length digital words. The bits steer the signal up
and down in tiny steps. The playback circuitry for this device is very simple,
so it would be easy to build a cheap portable, perhaps playing 8-centimetre
discs.
But the ARA is not happy about Sony鈥檚 plans. It points out that the signal
streams down each of DSD鈥檚 channels at more than 2.8 megabits per second,
allowing less playing time in multichannel surround sound than is available from
a conventional stereo CD. Sony counters that the system can be scaled down for
consumer use by cutting down the sampling rate, and so reducing the bit rate in
the data stream.
Malcolm Hawksford of the Centre for Audio Research and Engineering at the
University of Essex warns that bit-stream processing has other problems. In a
research paper posted on the Internet by the ARA, he says that it would be
difficult to build digital tone controls to work with DSD, and that including
them in a player would put up the price. Hawksford concluded that the advantages
of the existing digital word system are 鈥渙verwhelming鈥�.
Samsung, which is not a member of the DVD consortium, is a late entrant to
the fray. The Korean company has worked with a British partner, Data Conversion
Systems, to make a series of music recordings that prove the practicality of
sampling sound at 192 kilohertz, with each sample coded in 24-bit words. Samsung
hopes to play the recordings to the consortium in the hope of stalling a
decision in favour of a competing system.
Sony and Samsung鈥檚 systems will capture frequencies of around 100
kilohertz鈥攖wice the ARA鈥檚 ceiling and much higher than the 20 kilohertz
upper limit to human hearing. Panasonic argues that by trying to capture
super-high frequencies, Sony and Samsung are going too far. 鈥淭here is nothing
meaningful at those frequencies. It鈥檚 just a hobby,鈥� says Ted Abe, head of
Panasonic鈥檚 audio technology group in Osaka. But advocates of these techniques
insist that while frequencies higher than 20 kilohertz are not heard
consciously, they do affect people鈥檚 perception of music. Also, filters used to
block frequencies above 20 kilohertz can seriously spoil the way lower
frequencies sound, so systems should be designed to cope with much higher
frequencies.
The ISC is now arranging listening tests around the world to compare the
competing systems. Choosing the best is going to be a tough task, says Tony
Griffiths, former technical director of the Decca Recording Centre in London and
a member of the ARA. 鈥淚t is even more difficult to compare audio systems than
video. You need to rationalise what is real, and what is emotional,鈥� he says.
鈥淚ssues like the best sampling rate are like a religion. You will never convert
people who believe in one rate to believing in another.鈥�
The ISC expects to put its final recommendations to the DVD consortium this
year so that DVD-Audio players can go on sale by the end of the century. Earlier
this year in a policy statement, however, it offered a foretaste of what
features it wants the new system to have.
First, the ISC insists that the new
disc must be a hybrid that will work with CD players. The disc carries two
recordings at different depths, using a technology developed by Philips, Sony
and the American company 3M
(see Diagram). Philips recently
demonstrated the hybrid system at its pilot pressing plant at Eindhoven in the
Netherlands.
The DVD-Audio recording is printed 0.6 millimetres below the surface while
the CD version is printed deeper down, 1.2 millimetres below the surface鈥�
the same depth as is used today for conventional CDs. DVD-Audio players will
read at 0.6 millimetres to pick up just the super-hi-fi recording. The 鈥減its鈥� in
the disc that carry this recording are lined with a film that reflects light at
650 nanometres, the wavelength of laser light set aside for DVD-Audio. But this
film is transparent to light at 780 nanometres, the wavelength used by CD
players. So CD players will read the recording at 1.2 millimetres and simply
ignore the DVD version above it, just as they read through dirt on the surface
of an ordinary CD.
Second on the ISC鈥檚 wish list is a demand that could bring the recording
industry something it has been after for at least 30 years. Every record company
would like to control copying of its discs, and indelibly mark its recordings so
that illegal copies can be identified and pirates brought to book. The ISC sees
DVD-Audio as a golden opportunity to launch a worldwide 鈥渁ctive copyright
management system鈥� that would build on the draconian copyright protection
already in place on DVD-Video players and movie discs. Each disc and player
carries a regional code, which identifies where it was bought. For this purpose,
the world is divided into six zones, with the US and Europe having different
codes. The player will only play a disc if their codes match, so DVD-Video
players sold in Europe refuse to play movie discs pressed for sale in North
America, for example. Record companies may see regional coding as an attractive
way to control trade in music discs.
DVD-Video also uses powerful encryption to foil anyone making a digital copy
of a movie from a pressed disc onto a blank one. Vital encryption keys are
stored in an area of the disc that the player does not feed through to an
external connection. A copy missing these keys will not play on a DVD player. A
DVD-Audio player could work in similar fashion.
Second line of defence
The ISC also recommends the use of embedded signalling for DVD-Audio. It
wants an inaudible 鈥渨atermark鈥� to be buried in the sound in such a way that it
will stay there even after the sound has been converted from digital to analogue
and back again, and transmitted over the Internet. This would provide another
line of defence against piracy. Future audio recorders could be designed to
identify the mark and block a recording. The IFPI is currently studying a number
of these copyright management systems
(This Week, 5 July, p 20).
All this may be music to the ears of the recording industry, but it risks
turning consumers off the whole idea of DVD-Audio. People accustomed to buying
CDs on holiday will not be pleased to find that their DVDs refuse to play on
their machines at home. And people who buy records expect to be able to copy
them, or favourite tracks, for private use and are unlikely to pay a premium for
a system that stops them doing this.
Even without these disadvantages, it may prove difficult to sell the idea to
consumers. 鈥淭here is nothing much wrong with the CD system,鈥� says Griffiths. 鈥淚f
there were, then studio engineers and producers would be jumping up and down at
what the CD system does to their recordings.鈥� Golden-eared hi-fi enthusiasts who
claim to be able to hear faults in the 44.1 kilohertz 16-bit coding system will
doubtless pay a premium for DVD-Audio discs, if only to prove how golden their
ears are. But these people are in a tiny minority.
The cost of pressing a hybrid disc is around 拢2, compared to 25 pence
for a CD. But if shops ask more for hybrids than for CDs, many people will stop
buying them. It seems then that the only way for record companies to start the
virtuous circle of disc and player sales is to cut profit margins on hybrid
discs so they can be sold at the same price as CDs. The high price of today鈥檚
CDs, which sell for around 拢15, suggests that this is something the record
industry will be reluctant to do.
While factions from the hi-fi and record industries remains locked away in a
darkened room, arguing the relative merits of rival technologies, in the world
outside life goes on. Dolby Laboratories has teamed up with American record
company Delos to release the first audio-only DVD-Video disc. It includes
recordings of Tchaikovsky鈥檚 1812 Overture and Richard Rodney Bennett鈥檚
Barcarolle. The disc carries a surround sound signal encoded with Dolby
AC-3 lossy compression. It plays on DVD-Video players to give home cinema
surround sound, without the moving pictures. The Japanese company Denon has now
released a similar disc of Beethoven鈥檚 music.
The appeal of these discs is obvious. To most people鈥檚 ears, there is nothing
wrong with the sound this gives them. If the idea catches on before DVD-Audio
takes off, the ARA鈥檚 worst nightmare and Dolby鈥檚 wildest dream look likely to
come true. The next generation will grow up with ears attuned to lossy
compression. Any hope for Ambisonics and the chance to hear Juliet calling down
to Romeo will be lost forever.