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Immink,
Hoogendijk
and
Kahlman:
Digital
Audio
Modulation
DIGITAL
AUDIO
MODULATION
IN
THE
PAL
AND
NTSC
LASERVISION
VIDEO
DISC
CODING
FORMATS
Kees
A.
Schouhamer
Immink,
Ad.
H.
Hoogendijk
and
Joost
A.
Kahlman
Philips
Research
Laboratories
P.O.B.
80.000,5600
JA
Eindhoven,
The
Netherlands
Abstract
We
present
an
extension
of
the
current
LaserVision
video
disc
format
that
includes
a
digital
audio
signal.
We
show
the
feasibility
of
a
combined
digi-
tal
audio
signal
according
to
the
Compact
Disc
Digital
Audio
format
and
the
current
analog
audio
signals
in
the
NTSC
video
format,
enabling
the
realiza-
tion
of
a
compatible
system.
For
the
PAL
and
SECAM
video
formats
we
show
the
feasibility
of
digital
audio,
but
unfortu-
nately
it
cannot
be
combined
with
the
analog
audio
carriers.
O.
Introduction
In
the
current
LaserVision
(LV)
video
disc
coding
formats
(NTSC,
PAL
and
SECAM),
the
ana-
log
audio
stereo
channels
are
frequency-modulated
and
added
by
means
of
pulse-width
modula-
tion
of
the
frequency-modulated
video
signal
(refs.
1,2,3).
The
maximum
audio
signal-to-
-noise
ratio
of
the
LV
525
lines
NTSC
format
at
present
attainable
is
approximately
70
dB,
which
includes
15
dB
im-
provement
by
the
CX
noise
re-
duction
system
(ref.
3).
In
the
625
lines
PAL
and
SECAM
formats
of
the
LV
the
audio
signal
is
approximately
10
dB
superior
to
the
NTSC
LV
format.
An
improvement
in
audio
quality
seems
possible
only
by
going
digital.
For
example
the
16
bits
linear
quantization
used
in
the
Compact
Disc
Digital
Audio
System
format
(refs.
4,5)
achieves
a
signal-
Manuscript
received
September
19,
1983
Contributed
Paper
0098-3068/83/C
-to-noise
ratio
of
96
dB.
Furthermore
the
powerful
error
correction
system
of
this
digi-
tal
format
has
a
beneficial
in-
fluence
on
the
effect
of
drop-
-outs.
In
this
paper
we
report
on
experiments
and
simulations
to
show
the
feasibility
of
adding
a
digital
audio
signal
according
to
the
Compact
Disc
Digital
Audio
format
in
the
current
LV
video
disc
formats.
The
bandwidth
of
the
digital
audio
signal
spectrum
(approximately
1.5
MHz)
and
its
modulation
index
on
the
main
carrier
are
of
great
importan-
ce.
The
disturbance
of
the
digital
audio
signal
in
the
video
picture
plays
an
impor-
tant
role
in
the
overall
design.
A
low
modulation
index
of
the
digital
audio
signal
results
in
a
poor
signal-to-noise
ratio,
giving
rise
to
a
high
bit
error
rate.
Many
experiments
have
been
done
to
arrive
at
a
com-
promise
on
these
conflicting
parameters.
In
Section
1
we
briefly
des-
cribe
the
LV
video
formats
and
derive
requirements
which
a
di-
gital
audio
modulation
system
should
meet.
We
describe
the
simulations
used
to
find
quan-
titatively
the
constraints
for
the
digital
audio
modulation
within
the
LV
coding
format.
In
Section
2
we
describe
the
expe-
rimental
results
obtained
with
actual
discs.
3543-0551$01.00
©
1983
IEEE
543
IEEE
Transactions
on
Consumer
Electronics,
Vol.
CE-29,
No.
4,
November
1983
1.
Requirements
to
be
met
by
digital
audio
modulation
systems
in
the
LaserVision
formats
In
this
section
we
describe
the
LaserVision
coding
formats,
and
give
the
particular
re-
quirements
to
be
met
by
a
digital
audio
modulation
system
in
order
that
it
can
be
added
to
the
current
LaserVision
formats.
1.1.
Description
of
the
Laser
Vision
coding
formats
The
signal
format
of
current
NTSC
and
PAL
LaserVision
is
a
two-level
signal
(HF)
which
is
frequency-modulated,
after
pre-
-emphasis,
by
the
composite
(luminance
and
chroma)
video
signal.
Addition
of
the
stereo
sound
signal
is
achieved
by
means
of
pulse-width
(duty-
-cycle)
modulation
of
the
HF-
-signal
by
the
two
frequency-
-modulated
audio
carriers.
Figure
1
shows
a
block
diagram
of
the
signal
path
of
the
en-
coder.
The
signal
xo(t)
is
the
frequency-modulated
composite
video
signal.
Signals
x1(t)
and
X2(t)
are
the
frequency-
modulated
sound
signals.
The
sum
signal
is
limited,
so
that
a
pulse-width
and
frequency-
x(t)
Figure
1.
Generation
of
the
modulator
signal.
The
sum
signal
is
limi-
ted
so
that
a
pulse-width
and
frequency-modulated
two-level
signal
results.
-modulated
two-level signal
y(t)
results.
Figure
2
depicts
the
principle
of
pulse-width
modulation;
x(t)
is
the
input
signal
to
the
limiter,
y(t)
is
the
resulting
two-level
output
signal.
video
y(t)
limiter
Figure
2.
Principle
of
pulse-width
modu-
lation;
x(t)
is
the
input
sig-
nal
to
the
limiter,
y(t)
is
the
resulting
two-level
output
sig-
nal.
Figure
3b
shows
the
spectrum
of
a
PAL
video
signal
which
is
frequency-modulated
on
a
carrier
of
7.1
MHz
(i.e.
the
frequency
corresponding
to
the
black
level
of
the
video
signal),
where
JO
is
the
prin-
cipal
component
representing
the
frequency
as
a
function
of
the
amplitude
of
the
video
sig-
nal.
Jl
is
the
first-order
lower
sideband,
also
referred
to
as
chroma
band,
which
is
situated
at
4.43
MHz
from
the
principal
component
JO,
4.43
MHz
being
the
frequency
of
the
chrominance
carrier
in
the
PAL
video
signal,
and
J2
is
the
second-order
sideband
which
is
mirror-inverted
(see
ref.
6)
relative
to
the
frequency
zero-
-point.
In
the
LV
PAL
format
two
frequency-modulated
audio
carriers
of
0.683
and
1.066
MHz
are
added
to
this
signal.
The
amplitude
of
the
sound
carriers
is
chosen
as
-26
dB
relative
to
the
main
carrier.
544
Immink,
Hoogendijk
and
Kahlman:
Digital
Audio
Modulation
Figure
3a
shows
the
spectrum
of
an
NTSC
video
signal
which
is
frequency-modulated
on
an
8.1
MHz
carrier.
Since
the
chrominance
carrier
in
an
NTSC
dB
0
t-20
-40
-60
-80
NTSC
Laser
Vision
standard
A1
A2
K
ii
0
1
2
3
4
5
6
7
8
N
freq.
MHz
sync
Jo
9
10
PAL
Loser
Vision
standard
dB
0
-20
-
Al
A2
-40
-60
-80
0
1
sync
JO
J2
2
.i
3
4
5
6
7
8
9
10
freq.
MHz
Figure
3a/b.
Frequency
spectra
of
the
NTSC
(a)
and
PAL
(b)
LaserVision
video
formats.
signal
has
a
frequency
of
3.58
MHz,
the
lower
sidebands
Ji
and
J2
are
now
spaced
at
distances
of
3.58
and
7.16
MHz,
respec-
tively.
In
the
NTSC
video
format
the
audio
signals
are
added
as
FM
carriers
at
2.3
and
2.8
MHz.
The
basic
idea
of
the
addition
of
digital
audio,
which
will
be
explained
in
detail
in
the
following,
is
to
use
the
low-end
frequency
range
up
to
1.75
MHz.
We
may
there-
fore
conclude
that,
unlike
the
case
of
PAL,
the
analog
carriers
can
even
remain
in
the
case
of
NTSC,
so
that
compati-
bility
with
analog
sound
is
possible.
The
interference
caused
by
the
second
order
sideband
J2,
found
in
this
low-end
frequency
range,
has
to
be
removed.
An
example
of
an
embodiment
of
such
a
system
is
given
in
ref.
7.
The
method
(see
fig.
4)
is
basically
a
compensation
method.
The
chroma
band
is
filtered
out
from
the
composite
video
signal.
By
means
of
a
squarer
circuit
and
bandpass
filtering
the
second
harmonic
is
generated.
This
frequency-
-doubled
chroma
signal
is
now
added
with
the
correct
phase
and
amplitude
to
the
original
composite
video
signal.
After
frequency-modulation
the
chroma
J2
component
will
be
cancelled.
5MHz
ws
2ws
A
co
m-P
Z
t
oto
optical
video
rmoduator
pre
emph.
CD
encoder
Figure
4.
An
example
of
the
compensation
of
the
second-order
side
band
J2.
1.2.
Picture
quality
To
find
the
effect
of
a
pulse-width
modulation
of
the
carrier
on
the
picture
quality
we
designed
the
experimental
set-up
shown
in
Figure
5.
The
video
modulator
supplies
a
com-
posite
PAL
video
signal
to
the
frequency
modulator.
The
sine-
wave
from
the
signal
generator
is
fed
to
the
pulse-width
input
of
the
modulator.
The
frequency
and
pulse-width
modulated
carrier
passes
a
circuit
which
simulates
the
frequency
roll-
-off
of
the
optical
read-out
system.
The
video
signal
can
be
545
IEEE
Transactions
on
Consumer
Electronics,
Vol.
CE-29,
No.
4,
November
1983
eol
dB
FM
disc
mod
ulator
simulator
I
pulse
-width
input
generato
Figure
5.
Block
diagram
of
the
experimen-
tal
set-up
to
study
the
in-
fluence
of
pulse-width
modula-
tion
on
the
picture
quality.
studied
with
a
video
demodula-
tor
and
a
video
monitor.
An
in-
formal
panel
examined
the
effect
of
the
pulse-width
modu-
lation
on
the
picture
quality
as
a
function
of
the
amplitude
and
frequency
of
the
signal.
We
determined
the
pulse-width
level
at
which
it
became
just
visible
in
the
video
picture.
To
achieve
the
maximum
visibi-
lity
of
the
disturbance
of
the
pulse-width
modulation,
the
frequencies
of
the
generator
were
chosen
at
even
multiples
of
the
line
frequency
(15625
Hz
for
PAL).
The
disturbance
in
the
video
signal
is
caused
by
the
second
order
sideband
of
the
pulse-
-width
modulation.
Figure
6
gives
the
maximum
pulse-width
level
that
can
be
allowed
as
a
function
of
the
generator
frequency.
The
graph
shows
that
the
influence
re-
mains
fairly
constant
up
to
approximately
1.5
MHz
and
in-
creases
rapidly
above
this
frequency,
due
to
direct
inter-
ference
in
the
video
FM
spec-
trum.
The
vertical
amplitude
axis
is
given
relative
to
the
amplitude
of
the
main
carrier.
Figure
6
illustrates
that
with
a
maximum
signal
level
pulse-
-width
modulation
may
be
applied
when-the
signal
is
passed
through
a
lowpass
filter
with
a
cut-off
frequency
in
the
range
from
1.5
to
2
MHz.
-20.
-
40
-60
0
is
2
MHz
Figure
6.
Relative
amplitude
of
sinus-
oidal
pulse-width
modulation
when
it
becomes
just
visible
in
the
picture.
The
video
decoder
is
an
unmodified
model
LV
720,
Mk-1
PAL
decoder.
1.3.
Interference
and
noise
In
optical
recording
the
signal-to-noise
ratio
at
low
frequencies
(
500
kHz)
deteriorates
as
a
result
of
the
interference
produced
by
the
He-Ne
laser
which
is
used
to
readout
the
video
disc.
Since
a
comparitively
weak
signal-
-strength
is
desirable
for
the
coding
of
the
digital
audio
signal
(see
Fig.
6),
it
is
ad-
vantageous
to
boost
the
signal-
-strength
at
low
frequencies
relative
to
the
signal
strength
at
higher
frequencies.
A
suit-
able
cut-off
frequency
is
situated
in
the
range
from
100
kHz
to
1
MHz,
in
particular
at
500
kHz,
because
at
approxima-
tely
500
kHz
the
EFM
spectrum
(EFM
is
the
modulation
system
used
in
the
Compact
Disc)
exhi-
bits
a
maximum
and
rolls
off
below
this
frequency
(refs.
8,9,10).
Figure
7
shows
the
frequency
diagram
of
a
suitable
low-frequency
pre-emphasis
filter.
The
roll-off
frequency
is
situated
at
500
kHz.
Below
this
frequency
the
signal
is
546
z
.5
Immink,
Hoogendijk
and
Kahlman:
Digital
Audio
Modulation
boosted
by
6
dB/octave,
which
is
easy
to
achieve.
The
cross-
-over
frequency
at
which
the
characteristic
becomes
flat
again
(in
the
present
example
30
kHz)
is
determined
by
the
visibility
limit
(Figure
6)
and
its
possible
influence
on
con-
trol
systems
such
as
the
radial
tracking.
During
our
experi-
ments
we
found
a
pre-emphasis
of
23
dB
an
optimal
choice.
dBf
Composite
Video
H
I
I
SIGNAL
PROCESSING
ENCODING
Audio
I
Audio
1I
Digital
Audio
Figure
7.
Amplitude
Bode
diagram
pre-emphasis
filter.
500k
1M
treq
of
the
1.4.
Complete
diagram
of
encoder
and
decoder
After
the
preliminaries
of
the
preceding
sections
i-t
is
now
quite
easy
to
draw
the
block-
diagram
of
the
complete
system.
Figure
8
shows
the
dia-
gram
of
the
combined
video
and
digital
audio
encoder.
We
deci-
ded
to
use
the
Compact
Disc
en-
coder
as
the
line
encoder.
In
other
words
the
bit
stream
supplied
to
the
pulse-width
mo-
dulation
input
is
bit-to-bit
compatible
with
the
normal
Compact
Disc
modulation
bit
stream.
It
is
clear
that
this
has
the
advantage
of
enabling
current
equipment
to
be
used
for
encoding
and
decoding
the
digital
audio
signal.
Accor-
dingly
the
digital
audio
signal
is
CIRC-encoded
and
EFM-modula-
ted,
and
the
subcode
generator
supplied
the
additional
infor-
mation.
The
two-level
output
of
the
EFM
modulator
is
lowpass-
Figure
8.
Block
diagram
of
the
combined
video
and
digital
audio
en-
coder.
The
block
diagram
holds
for
the
PAL
and
NTSC
video
for-
mats
with
some
altered
para-
meters.
Note,
however,
that
the
analog
audio
carriers
have
to
be
removed
in
the
PAL
case.
The
video
FM
modulator
is
extended
using
J2
compensation.
-filtered
with
a
cut-off
fre-
quency
of
approximately
1.75
MHz.
After
the
low-frequency
pre-emphasis
the
signal
is
applied
to
the
pulse-width
in-
put
of
the
video
modulator.
Figure
8
holds
functionally
for
both
the
NTSC
and
PAL
cases,
with
of
course
some
altered
parameters.
Note,
however,
that
in
the
PAL
video
format
the
analog
audio
carriers
have
to
be
removed.
The
level
of
the
digital
audio
signal
with
res-
pect
to
the
main
carrier
is
approximately
-22
dB.
In
Figure
9a/b
we
have
depicted
the
re-
sulting
spectra
in
both
the
NTSC
(a)
and
the
PAL
(b)
formats.
547
IEEE
Transactions
on
Consumer
Electronics,
Vol.
CE-29,
No.
4,
November
1983
dB
freq.
MHz
dB
0
sync
JO
1
2
3
4.
5
6
7
8
9
10
freq.
MHz
Figure
9
a/b.:
Spectra
of
the
combined
digital
audio
and
the
NTSC
(a)
and
PAL
(
b)
vidDeo
formats
.
Figure
10
shows
the
block
dia-
gram
of
the
decoder.
The
digi-
tal
audio
signal
can
easily
be
SIGNAL
PROCESSING
DECODING
Figure
10.
Block
diagram
of
the
decoder.
The
EFM
signal
is
simply
recon-
structed
by
de-emphasis
and
lowpass
filtering.
reconstructed
by
de-emphasis
and
lowpass
filtering.
The
low-
pass
filter
cut-off
frequency
is
1.75
MHz.
After
this
filtering
the
signal-is
passed
to
a
normal
Compact
Disc
deco-
der
which
eventually
supplies
the
audio
signal.
The
video
decoder
does
not
need
any
functional
changes
with
respect
to
the
current
one.
2.
Experiments
The
digital
audio
signal
can
be
disturbed
by
different
sour-
ces.
These
disturbances
may
originate
from:
1.
irregularities
on
the
video
disc
surface,
2.
birefringence
of
the
disc
substrate,
3.
crosstalk.
We
recorded
many
experimen-
tal
discs
(NTSC
and
PAL)
to
measure
the
effect
of
these
sources
of
interference.
2.1.
Irregularities
on
the
video
disc
surface
EFM
tests
sequences
(pseudo
music)
written
directly
on
the
disc
as
a
pulse-width
modula-
tion
of
the
pits,
with
levels
varying
from
-30
to
-20
dB
with
respect
to
the
main
carrier,
are
hardly
detectable
with
suf-
ficient
bit
error
rate
(BER)
without
pre-emphasis.
The
low-
-frequency
disturbance
are
due
to
scratches
and
rapid
fluctua-
tions
of
the
reflection
coeffi-
cient
of
the
video
disc.
After
pre-emphasis
as
in
Figure
7
we
found
BERs
in
the
range
10-5-1o-6
without
the
EFM
sig-
nal
being
visible
in
the
video
picture.
548
Immink,
Hoogendijk
and
Kahlman:
Digital
Audio
Modulation
2.2.
Birefringence
of
the
disc
substrate
A
source
of
interference
with
the
EFM
signal
is
the
birefringence
of
the.
video
disc
when
a
He-Ne
laser
is
used
for
read-out.
The
birefringence
of
the
measured;discs.reached
up
to
250,
resulting.in
a
certain
fraction
of
light
intensity
being
reflecte.d
by
the
disc,
but
not
reflected
to
the
signal
detector
by
the
polar,izing
beam
splitter
and
hence
fed
back
to-
wards
the
laser.
The
frequency
of
the
light-intensity
modula-
tion
due
to
this
laser
feedback
depends
on
the
frequency
at
which
the
length
of
the
optical
light
path
changes.
For
a
disc
rotating
at
a
speed
of
n
rev/sec
the
fundamental
frequency
f
is
f
=
2sn/A
where
s
is
the
total
stroke
of
the
unflat
disc
and
A
the
wavelength
of
the
He-Ne
laser.
At
s=2
mm,
A
=
633
nm
and
n=25
rev/sec
this
frequency
equals
160
kHz.
Other
unflat
modes
of
the
disc
may
cause
higher
harmonics.
In
practical
situations
unflat
discs
can
give
amplitude
modu-
lations
of
the
light
output
of
the
He-Ne
laser
at
frequencies
up
to
500
kHz.
With
deliberately
warped
test
discs
we
found
amplitude
varia-
tions
at
frequencies
up
to
350
kHz.
We
measured
the
maximum
tolerable
birefringence
of
the
disc
substrate,
where
the
digi-
tal
audio
signal
is
just
dis-
turbed
(the
appearance
of
in-
terpolations
and
mutes
in
the
decoder).
The
effect
of
bire-
fringence
of
the
test
discs
can
be
increased
by
increasing
the
amount
of
light
fed
back
to
the
laser.
This
can
be
obtained
by
a
rotation
of
the
quarter-wave
plate
in
the
video
disc
player
round
the
optical
axis.
Our
measurements
showed
that
the
BER
of
the
EFM
pseudo
music
signal,
at
a
level
of
-26.
dB,
are
not
seriously perturbed
by
the
birefringence
of
the
disc
up
to
300.
c.
Crosstalk
Another
possible
source
of
interference
with
the
EFM
sig-
nal
is
crosstalk
due
to
an
obliqueness
of
the
disc
sub-
strate
relative
to
the
perpen-
dicular
position
of
the
optical
axis
of
the
read-out
objective
lens
in
the
video
disc
player.
At
the
nominal
track
pitch
of
1.67
microns
and
at
skew
angles,
in
the
radial
as
well
in
the
tangential
direction,
up
to
1°
we
were
unable
to
measure
any
increase
of
the
BER
of
the
EFM
test
sequences
(written
at
levels
varying
from
-26
to
-20
dB).
3.
Conclusions
The
current
LaserVision
video
disc
system
can
be
com-
bined
with
digital
audio
accor-
ding
to
the
Compact
Disc
Audio
System,
fulfilling
the
require-
ments
that:
a)
the
digital
audio
signal
is
not
visible
in
the
video
pic-
ture,
and
b)
the
digital
audio
signal
can
be
readout
well
within
the
limits
of
the
CIRC
error
correction
system,
even
with
disturbing
influences
ori-
ginating
from
imperfections
of
the
disc
and/or
the
read-out
system.
Contrary
to
the
case
with
PAL,
the
analog
carriers
can
even
remain
in
the
case
of
NTSC,
so
that
compatibility
with
analog
sound
is
possible.
The
digital
audio
signal
can
easily
be
reconstructed
by
fil-
tering
and
decoding
by
the
EFM
and
CIRC
decoder.
Eindhoven,
June
1983
549
nm
IEEE
Transactions
on
Consumer
Electronics,
Vol.
CE-29,
No.
4,
November
1983
References
1.
P.
Bogels,
"System
coding
parameters,
mechanics
and
electro-mechanics
of
the
re-
flective
video
disc
player",
IEEE
Trans.
Consum.
Elec.,
pp.
309-317
(1976).
See
also
IEC
Draft
-
UAR-1605-222/8304.
2.
H.
Vaanholt,
"The
coding
format
for
composite
PAL
video
signals
and
stereo
sound
in
the
LaserVision
op-
tical
videodisk
system",
The
Fourth
International
Confe-
rence
on
Video
and
Data
Recording,
Southampton,
pp.
351-365
(1982)
See
also
IEC
Draft
UAR-1605-223/8304.
3.
G.
Badger
and
R.
Allen,
"The
audio
side
of
the
Laser
video
disc't,
72nd
Convention
AES,
preprint
1935
(1982).
4.
L.B.
Vries
et
al.,
"the
Digital Compact
Disc
System:
modulation
and
error
correc-
tion",
67th
Convention
AES,
preprint
1674
(1980).
5.
M.G.
Carasso,
J.B.H.
Peek
and
J.P.
Sinjou,
"The
Compact
Disc
Digital
Audio
System",
Philips
Tech.
Tev.,
vol.
40,
pp.
151-155
(1982).
6.
M.R.'de
Haan
and
C.H.F.
Veizel,
"Intermodulation
and
moire'
effects
on
optical
video
recording",
Philips
Res.'Reps.,
vol.
32,
pp.
436-459
(1977).
7.
C.H.
Coleman,
"Moire
inter-
ference
reducing
circuit
for
FM
video
recorders",
U.S.
Patent
4,
052,
740
(1977).
8.
J.P.J.
Heemskerk
and
K.A.
Schouhamer
Immink,
"Compact
Disc:
system
aspects
and
mo-
dulation",
Philips
Tech.
Rev.,
vol.
40,
pp.
157-164
(1982).
9.
K.A.
Schouhamer
Immink
and
U.
Gross,
"Optimization
of
low-frequency
properties
of
eight-to-fourteen
modula-
tion",
Radio
and
Electronic
Engineer,
vol.
53,
pp.
63-66
(1983).
10.
H.
Ogawa
and
K.A.
Schouhamer
Immink,
"EFM
-
The
Modula-
tion
for
the
Compact
Disc
Digital
Audio
System",
Premier AES'Conference,
Rye-
town
(1982).
550
Immink,
Hoogendijk
and
Kahlman:
Digital
Audio
Modulation
BIOGRAPHIES
Kees
A.
Schouhamer
Immink
joined
the
Philips'
Research
Lab-
oratories
(Eindhoven)
in
1968.
He
obtained
after
a
part
time
study
a
master's
degree
in
electronics
at
the
Eindhoven
University
of
Technology.
He
then
joined
the
Measurement
and
Control
group
of
the
Philips's
lab
to
study
the
servo
systems
of
the
LaserVision
system.
In
1979
he
reinforced
the
optical
disc
recording
group
to
design
channel
codes
for
the
Compact
Disc
Digital
Audio
System.
His
present
interests
are
modulation
systems
for
magneto-
optical
and
magnetic
recording.
Joost
Kahlman
was
born
in
Tilburg,
the
Netherlands
in
1956.
He
received
the
B.Sc.
degree
in
electronics
in
Eindhoven
in
1979.
He
joined
the
Philips
Research
Laboratories
in
1980
after
serving
the
Dutch
army.
He
is
now
engaged
in
the
design
of
modulation
systems
for
optical
disc
systems.
Ad
H.
Hoogendijk,
a
member
of
the
Main
Industry
Group
Audio,
N.V.
Philips'
Gloeilampenfabrieken,
Eindhoven,
the
Netherlands,
received
a
bachelor's
degree
in
electronics
in
1959.
At
the
present
time
his
responsibility
is
audio
and
video
signal
processing
for
the
LaserVision
video
disc
system.
Between
1963
and
1972
he
performed
similar
work
for
VCR
and
other
video
tape
recorders.
551
