reported
by: Dr. Roland K C Tan
Section Advisor
(Term 1998/99)
On Friday, 18 December 1998 at
7.00pm, 11 members and 25 guests of the AES Singapore Section gathered at
TOUCH Community Theatre to listen to a talk on "The Compact Disc Story" by
Dr. Kees A. Schouhamer Immink*. A professor at the Institute of Experimental
Mathematics, Essen University in Germany and also Fellow
Member of the AES and Vice President
of the AES Northern Region in Europe, Dr. Immink is currently in Singapore
for 3 months as a Visiting Professor at the National
University of Singapore (NUS).
|
The audience,
comprising of AES Singapore Section members and guests, in full
concentration and 'all ears' to Dr. Immink's talk at the Touch Community
Theatre - photograph by Stephen Low |
Before the evening's presentation,
Mr. Jibby Jacob, current Chairman of the AES Singapore section, gave the
opening address before introducing the speaker. In his
speech, members were reminded to
renew their memberships. At 7.45pm, Dr. Immink began his talk by giving a
brief summary of the history of compact disc (CD) where he was involved in
its standardization while he was with the Philips Research laboratories in
Eindhoven, The Netherlands. He also talked about the future of audio
recording mediums such as the new digital versatile disc (DVD) and
DVD-plus.
The storage density of recording
medium has been growing gradually since the original cylinder developed by
Edison to the recent DVD. In fact, the storage densities
have grown by more than 1 million
times greater than those available at the end of the last century. The
evolution of audio discs have indicated that it was at least 10 years after
Edison's cylinder invention before Berliner and others invented a method of
disc recording. The stereo LP record introduced in 1958 delivered a major
step in sound quality. However, as far as optical recording is concerned,
everything before 1969 is prehistory!
In consumer electronics, CD is the
most important development since the introduction of television. According
to Dr. Immink, the development of an audio disc with optical read-out
started at Philips Research in early 1973. In those days, solid-state lasers
were not available so the first experiments were conducted with LEDs, gas
lasers, and lamps. Analog wide-band frequency modulation was tried. However,
it soon became evident that it was inadequate. The advent of ever-cheaper
and faster digital circuitry made feasible the use of digital audio. The
main advantage that digital implementation confers over analog systems is
that in a well-engineered digital recording system the sole significant
degradation takes place at the initial digitization, and the quality lasts
until the point of ultimate failure. On the other hand, the quality of
analog recordings just fades away.
Sony and Philips demonstrated the
first prototypes of a digital sound system using a laser disk in 1977-78. In
1979, Sony and Philips decided to join forces to develop a world standard
for CD. This strategic alliance was based on the fact that Philips had
considerable expertise in optical technology, servo systems, and digital &
analog modulation systems. On the other hand, Sony had expertise in error
correction, PCM adaptors, and in channel coding. In other words, Philips
provided the "physics" of optical and Sony provided the digital audio
technology. There was also a marketing reason behind these as both were
small companies at that time.
A total of six meetings took place
between the Sony and Philips engineers in 1979-80 at both Tokyo as well as
Eindhoven. Two working prototypes were demonstrated - a Sony's 30-inch
optical disc and a much smaller diameter disc of 11.5cm by Philips.
Decisions had to be made concerning the main parameters such as the disc
diameter, playing time, sampling frequency, error correction system,
modulation system, and so on.
A decision was made during the 4th
meeting on March 1980 to adopt the sampling frequency at 44.1 kHz, 16-bit
resolution, and the cross interleaved Reed-Solomon code (CIRC) for its error
correction system. A sampling frequency of 44.1 kHz was selected as opposed
to 44.056 kHz simply because it was an easier figure to remember. The figure
of 44.056 was the result of a need for compatibility with the NTSC and PAL
video formats used for audio storage at the time. Sony developed the PCM
adaptor which could record PCM audio onto a consumer analog video tape
recorder. This unit used a non-standard sample rate that was convenient for
formatting PCM audio into the NTSC television lines. The video lines, frame
rate, and bits per line determine the sampling frequency one can achieve in
order to store two channels of audio. The final decisions were made during
the 6th meeting on June 1980 and the first version CD originally designed at
11.5cm diameter by Philips was finally changed to 12cm due to simpler metric
measurement. The smaller diameter disc was chosen because Philips felt that
the size of a CD should not be much larger than the successful analog
compact cassette invented in 1969!
|
Dr. Kees Immink
(14th from left) with members and guests of the AES Singapore Section
after his presentation - photograph by
Stephen Low |
Since the introduction of CD in
1980, the sales of LP has been declining gradually while at the same time an
exponential increase in CD sales was registered over the first decade
exceeding 1 billion CDs. The sales of CD players had climbed sharply between
1983 to 1990 reaching more than 40 million units while surprisingly, the
sales of LP turntables had remained almost constant at around 25 million
units. Dr. Immink also highlighted to the audience the numerous other
"books" in the CD standard. Among them, the Yellow Book for CD-ROM, Orange
Book for CD-Recordable, Green Book for CD-i, and White Book for Video CD
besides the Red Book for CD-Audio.
Before concluding his talk, Dr.
Immink gave some predictions for the future of optical disc medium based on
DVD. A comparison of DVD and CD-ROM main parameters show the new disc has a
capacity that is some seven times larger than CD. The data capacity of a
single layer single-sided DVD is 4.7 GBytes and for a single layer
double-sided is 9.4 GBytes. A CD-ROM has only a data capacity of around 650
MBytes. A number of different characteristics have led to the increase in
capacity of DVD when compared to CD. First of all, a thinner disc allows
more data to be stored since it minimizes error in focal point of the laser
beam due to disc tilt. Basically, a thinner disc can accommodate more tilt
errors. That is why the design of DVD has a disc thickness of only 0.6 mm
while that of a CD is twice as thick at 1.2 mm. CD has a density of 1
bit/mm2 while DVD has a density of around 6-7 bits/mm2. The greatest
capacity gain depends very much on the wavelength of the laser beam and also
on the thickness of the disc. It was also predicted that future disc could
be as thin as 0.2 mm and that DVD would replace CD as the optical disc of
the next millennium. Dr. Immink believes that by the year 2002, a 20 GBytes
DVD would materialize with a density of up to 20 bits/mm2. And by the year
2006, we shall see a 40 GBytes DVD with density reaching up to 50 bits/mm2.
|
Dr. Kees Immink
during the question-and-answer session after his talk -
photograph by Stephen Low |
Many questions were raised during
the Q&A session which lasted for more than 15 minutes. In his reply to a
question as to whether the new Super Audio CD (SACD) developed recently by
Philips and Sony could pose a "threat" to DVD as the disc of the future, Dr.
Immink does not think so. SACD, although fully backward compatible to Red
Book CD, still require a different type of player in order to playback the
high-density layer that is recorded separately on the SACD. That would mean
another new investment on top of a CD player and a DVD player. These add
extra cost to the consumers.
|
AES Chairman
Singapore Section, Mr. Jibby Jacob (right) presenting the momentous to
the speaker, Dr. Kees Immink, after his talk on 'The Story of Compact
Disc'. -photograph by Stephen Low |
One
member of the audience was also curious to know whether Philips and
Sony, in the course of CD standardization between 1979 to 1980, had
considered incorporating CD in a cartridge housing much like the current
floppy disc. It was felt that this idea could protect the disc from
scratches and other likely physical abuses. According to Dr. Immink, it
was believed that the design of CD at that time was such that it should
be something that people can "touch and feel" like an LP. Moreover the
thickness of the disc does not make it very feasible. However, with the
much thinner DVD of the near future, this is not entirely impossible. |
In a reply to another question,
the higher density disc of the future would not increase the overall bit
error rates (BERs) because of the development of more powerful error
correction algorithms which can reside in lower cost memory devices.
The meeting ended at around 9.14pm
and leaving especially the younger members among the audience with much
appreciation of the evolution of the optical discs. The AES Singapore
Section would also like to thank their fellow committee member, Mr. Robert
Soo, Technical Director of Touch Music, and his colleagues for the use of
the community theatre and their kind assistance during the meeting.
Interested readers can
find out more information from a recent paper published in the Journal of
the AES, Vol.46, No.5, pp 458-465 entitled "The Compact Disc Story" by Dr.
Kees A. Schouhamer Immink.
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