THE AUDIO SIDE OF THE LASER VIDEODISC
Greg Badger and Richard Pioneer Video, Inc. Costa Mesa, California
(F-5)
Allen
Presented at the 72nd Convention
1982 October
1935
__'_
23-27
Anaheim, California Thispreprint has been reproduced from the author's advance manuscript, without editing, corrections or consideration by the Review Board. The AES takes no responsibility for the contents. Additional preprints may be obtained by sending request and remittance to the Audio Engineering Society, 60 East 42nd Street, New York,New York 10165USA. All rights reserved. Reproduction of this preprint, or any portion thereof, is not permitted without direct permission from the Journal of the Audio Engineering Society.
AN AUDIO ENGINEERING SOCIETY PREPRINT
THE G.
O.
the
program
beginning
has
been
mere
helper
This
philosophy
program
-
to
with
the
OF
R.
THE
LASER
Allen,
VIDEODISC
Pioneer
audio
in
video
As
MCA
optical offer
music
as
Philips
videodisc, high
achieve
laser
the
United NTSC
channels
quality
that
The
Video,
Inc.
in
reaches
video
States
compatible of
of
the
nadir
when
that
the
cable brought
A generation
raised
of music The
developed they stereo
editing
is
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video.
of
videotape
the recorders
examine
are
with on
the
experiencing
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high
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standards agreed
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a demand
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That
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program
of most
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growth
audio
hand-maiden.
recording
its
average
the
fidelity
arrived.
the
the
laser
medium
assiduously
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goal.
optical
educational,
conveyer
reproduction
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broadcasting,
improvement.
stereophonic
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Fortunately,
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system
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dreadful
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and
Badger
SIDE
Introduction
Since
are
AUDIO
audio and
videodisc for
four
has
been
years.
television prograrm_ing entertainment
It
signal for
a
commercial is
and
a wide
applications.
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capable two
high
variety
reality of
in
providing
quality of
It is
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only
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so
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player
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disc
reflective
focus.
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11).
fingerprints of
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center
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the
disc,
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approximately
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compensation
for
differences
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tracks
by
the
RF
correction
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they
electrical
amplified
outer
diodes contacts
because
into
the
the
subsequently
level
onto
photosensitive
never out.
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circuit,
37
RF db
between audio
the
focused and
are
out
signals (figure inner signals
12.)
are
retrieved
by
signal.
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bandpass
filters
detector
stages
ocourence causes
of
the
voltage
lowpass
lowpass
signals
microprocessor
appearing
are
audio
circuits
before
decoder.
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for
100%
4.
Audio
to
noise
ratios to
Although down
with
or
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to
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decoder
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through
pass
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audio
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noise
and
usec
deemphasis
reduction through
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for
playback
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to
unweighted
peak
58 and
db,
between
ratio RMS
audio
respect
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passed
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frequency
Ratio
(VCNR)
to
hold
The
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separate
detector
The
control
CX
the
via
Characteristics
have
noise
carrier
of
FM
signal.
respective
are
television
Noise
to
switching.
RF
channels.
channels
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available
Channel
discs
signal audio
are
audio the
of
composite
quadrature
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loss to
the
separated
to
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applied
outputs
are
detected
switching
standard
Typical
and
deviation)
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the
applied
being
and
over
Signal
the
of
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audio
channel
after
amplifiers
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during
audio
and
obtain
demodulated
under
signals are
dropouts
value
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filtering
between noise
the
and
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38
video
63
are
43
fall at
carrier,
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video
producing
db.
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between a
level a
carrier
10
a video to peak
25 and of db
to
20
35
to
reduction
db.
26 db in
noise
level
audio
channels.
Carrier 58
db
audio
and
Frequency
and
the
KHz
the
vary
audio
minimum
of
bandwidth
deemphasis,
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translates at
where
to
the
slightly
the
the
25
db
output
CNR
is
of
the
Audio
approximately
depending
the
LaserDisc
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75
usec
deviation
of
deviation
after
that
the
level
of
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the
on
disc
measured.
audio
the
subcarrier
and
their
limiting,
and
has
been
maximum
limited
in
to
compression.
established
filters
significant
used,
The
is CX
levels
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curve.
subcarriers
preemphasis
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audio
at different
preemphasis
frequency
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to
player
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pass
with
attenuation.
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defined
as
6 db
headroom
of
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narrower
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radius
overall
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maximum
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VCNR
track
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partially
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The
to
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150
75
the
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Ratio
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With
to Noise
player.
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is afforded
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KHz
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50 KHz
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redefined
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This
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reduces available
deviation
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SNR on
by
a
2 db
the
level
40%
on
with
preemphasis
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KHz
above
Subsequently,
LaserDisc
the
0 db
at
1 KHz
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at
all
(figures
13
and
disc.)
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14)
input,
allowing
0 reference
modulation 2 db
was
reference
(_ 40
KHZ
frequencies
show
audio
has
deviation). and
headroom
Compare
this
typical
music
cassette,
a
15.)
It can
seen
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with
due
to peak
may
be
peak
Any
disc
and
of
the
consumer the
first
video
below
Residual
Channel
audio
on
area noise
player the
of
the
response
broadcast,
the
modulator
at
high
tape
of
a
LP
disc
compares
Any
attention
during
and
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careful
slight
loss
frequencies
to
high
frequency
mastering.
timebase
if
the
disc
replication
to
disc
and
as
30
not
a
corrected this
mirror
timebase on
errors
all
FM
Hz
errors.
also Wow
LaserDisc
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used
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modulation
16). is
and
disc
player
frequency
(figure
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to
process.
player
component
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due
In
the
removed
by
to
reduce
flutter
are
programs.
Noise
concern
relies
servo
to
disc
player
during
video.
that
primarily
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of
assigned
tangential line
from
servo
typically
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during
LaserDisc
order
FM
fidelity
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tangential
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is
manifested
audio
typical
the by
to
Errors
varies
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in for
eccentricity
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high
response
equalization
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influence
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compensated
Timebase
track
frequency
clipping
levels
Audio
new
to
vertical on
the
During
One
signals of
color the
engineers
flyback
several
track. is
audio
the burst
vertical
-8-
and to
is the
at
the
interval
residual
vertical
keep
signals
the
the
used
laser
beam
in the
beginning and
interval.
of
blanking
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periods,
no
color
Consequently, phase due
is
present
in
may
be
present
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the
audio
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modulation
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burst
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of
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during
on
LaserDiscs
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of
lower
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of
residual
level
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blanking.
Transform
reveal
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NTSC
carriers
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the
period
After
the
audio
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modulation
energy
harmonics.
Distortion
Sibilance audio
levels
release
or
master
or
after with
audio
in
the
carrier
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of
due
to
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in place
of PPM
playback
of
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excessive. to
audio
or
VU
with
discs
fluctuations
player
the
client due
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excessive The to
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eliminated
audio
peak
detecting
has and
-9-
been
distortion caused
dropouts
on
overall with
noise
monitoring
Occasional
audio
maintain
equalization,
level
to
frequency,
matters be
or
narrative
audio
complicate
and
meters.
quality
the
to excessive
difference
necessary
levels,
preemphasis
typical
generate
This
techniques,
on
preemphasis.
machine
sometimes
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harmonic,
audio
mastering
are
causes
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within
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carrier
levels
usually present
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deviation
program
RF
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high
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distortion
distortion tapes.
overmodulation soundtrack
is
by the
carrier LED's during excessive disc.
Dropouts
Crackle
on
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uncompensated carrier
or
due
subcarrier in the
to
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sample
began. disc
The
ultimate
discs
almost
5.
CX
While
Noise
Reduction
sufficient
for
To
studied
the
version
many
for
the
compression
LaserDisc
this
are
these
and
of
CX
basic
reduction,
LaserDisc
discussed
several
noise
applicability
in
than
the
chosen
would
be
most
systems
noise
spectrum
was
a modified
for
CX
17).
specifications Appendix.
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is
circumstances
reduction
to
finally (figure
the
of
are
player
audio
expansion
careful
dropouts
range
dynamic
system
in
Discs
fewer
wider
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problems.
the
system
by
dropout
conditions.
are
end,
noise
maintains
lies
noise
limiter
possible
a detected
considerably of
as
which
dropouts
room
use
far
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the
impulse
as
player
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of
there
The
CBS
to
of
applications,
their
LaserDisc. of
of
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quality
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with
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audio
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solution
entirely
the
where
levels
exhibit
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when
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threshold
corrected
in
under
manufacture
earlier
were
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manufacturing
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circuit
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defects
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hold
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channels
partially
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spikes.
audio
audio
This
on
version
of
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system
quality
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transmitted
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of
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Hz.
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for
to
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In
interference
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fact,
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of
material.
outlined
overshoots
of
In
sound
4K Hz
characteristics
levels
picture the
most
lowered high
signals.
overview
necessary
to
understand
noise
spectrum
ratio
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more
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than
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due
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to the
available db
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how
in
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output
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video
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specification
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level
brief
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level
with
deviation
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modulation
attack
signal.
bright,
decoding)
high
disc
which
scheme
quality
marketing
maximum
noise
modulation
the
standard
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with
frequency
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compansion
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good
inventory
LaserDisc.
increased
audio
encoded
prefer
band
within
typical
CX
single
listeners CX
the
with
resulting
allow
wide
program
of
compatible
for
"knee"
of
that
which noise
able The
amount
fact
could floor at
encoder/decoder
which
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to
deal
with
the
compression/expansion perceived
few
noise
videodisc
tolerate on
is
a the
an
single
reduction
source increase
of
inventory
compressor
reverts
from
2:1
below
to
the
0 db
modulation
on
frequency prevent with
1:1
in
reference playback
the
undecoded
CX
in
_ manner
not
alternation time
slow
in
small
changes
figure
The
noise
audio
signals
AC
high
signal
outputs VCA's
The decay
of for
signal (10
also pass
has
filter
is converted the
two
both
tone
burst
voltage
to a
a DC
rectifiers
of
wave
no
not.
fast
the
passes
circuit.
through
and
shown
the
the
two
amplifiers.
which
passes
through
rectifier. The
higher
controls
the
final
Such
a
fast
circuit,
-12-
attack if
in
encoder, through
level.
a
and
distortion.
encoder,
controlled
full
or
are
tracking
the
loop
and
dynamics
decoder
image
In
feedback
to
performance
modulation
and
decoder.
Here
gain
(1 mS)
used
a
the
peak of
channels.
next mS)
encoder
interfering
CX
between
in music
induce
process.
a
dynamic
alternate
CX
through
the
system
could
to
from
of
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-13-
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can ear
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and
paths
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music
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only
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large
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decays,
and
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Namely,
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signals
its
attention
on
persists
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or disc
noise.
This
an undesirable
when
music.
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filter,
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diode
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200
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ear
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during
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and
the
same
control
circuit
configuration
to
restore
the
state.
-14-
is
audio
in
a
signal
2 S
now
undesirable
output
to
as
CX
signal.
the
voltage
controlling
VCA's.
decoder,
tape
soft
noise
current
gain
audible
the
component from
focus
masks
and
Even
to
level
to
a
the
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functions
steady
a
become
two
will
begin
adjust
on
for
As
ear
If
then
decay.
will
mS
music.
may
only
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readjusted
a
forward-
longer
longer
remaining
for
music
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serves
to
swishing
has
appear
200
only
agaSn
continue
change
music
(decays).
level,
the
in
response
signals
primary
F 3 works
response
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about
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mS,
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it will
of
to
a rapid
the
effects
output
reverse-biased any
provides
occurring
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breathing
F 3 allows
period
are
after
200 mS,
but
S.
loud
rapidly
the
2
prevents
listening
after
circuit,
is
in reverse-biased
decays
readjust
operation,
changes
constant
(attacks)
changes
signal
no major
its
functions. biased
when
in
feedto
its
6.
Evaluation
One of
of
the
the
CX
LaserDisc
its
quality
factors
for
It all
for
analogue
for
tape
on
is
final
with
magnetic
2.
1/2"
four
track
present
no
disc.
or
be
Any
the
the
be
that
range fully
limiting
production
processing
audio methods
guidelines
reviewed.
be
that
avoided
Typical
Processinq
dynamic
used
shortcomings
arguing
optical
tape
generated
during
of
multiple to
audio
noise analogue
preserve source
program
media
used
the
majority
chains
is
to
media
for disc
Dolby
stereo,
necessary
A
range
19). or
with
videotape
stills.
audio
(figure
soundtracks.
synchronized
A brief
Dolby
often,
reduction
is on film.
dynamic
audio
materials
are
will
on LaserDisc
preserve
wide
Audio
include:
audio
time,
and
audio
noise
must
mastering
computer
disc
generations.
Film
the
media
buildup
the
too
Optimal
audio
1.
At
All final
there
noise
videodisc
or
source
tape.
that
aside,
integrity
finding
source
is mandatory
generation
the
the
source
Quality
of having is
of
common
reduction
Media
capabilities.
the
most
Source
challenges
utilize
used
of
entertainment
understand If a film
dbx
and
of
review
noise
prevent
-15-
of the
programming A and
processing will
reduction noise
be
of
this
released
will
buildup
B film
be
in
used
during
to
each
magnetic the
film
microphones
dialogue,
music
Dialogue
each
to
the
pass
filter
the
surround
surround
in the
pass
Low
35mm the
film.
The
B chain
high
4 to
This
master.
augment
the
1,
3, 5
the
compensation
the
the
and
the
audio
in
audio
A chain
ends.
for
cell
-16-
is
7 KHZ
the
to modified
a two is
released
signals
are
6, respectively.
two
projecter
point,
applied
and
and
right
and
are
picture
are
response
mono
picture
produce
four
signals
bass
records
at
If
to
and
this
filter
channels
from
center,
the
reduction
encoder
format,
If
one
mixed
At
left,
pass
front
a matrix
is where
begins
frequency
three
enhancement
printer
high
B noise
tracks
or
rolls
track,
always
screen.
an
three
music
almost
produced. Hz
with
and
stereo
of
original
least
dubbed
is the
the
finished
have
(mono
is 100
The
channel
bass
optical
master
Dolby
on magnetic
2 and
behind
printing
six
frequency
tracks
and
will
dialogue
stereo,
through
optical
recorded
be
channel)
track.
70mm
may
consists
stage At
These
magnetic
low
system.
film
chain
dubbing
the
speaker
A
record
for
stereo
four
optical
a
to
generated
However,
in Dolby
on
replacement
center
The
used
rerecorded
are
tracks.
surround
channel
effects.
A
a synchronized and
and
element.
sources.
effects fed
equipment
film
audio
generation.
and
dialogue
of magnetic
many
tape
is often
automatic
for
or
recorded the
on
theatre.
channels
The
next
to
solar
cell.
It
provides
slit
loss.
If
it
is
Dolby
stereo,
a frequency decoded,
the
response
passes
used
in advanced
with
a high
delayed,
that
listener's
The
Haas, any
optical
or
The
four
for
auditorium
For
mono
stereo Dolby
channel
the power
remove
noise
from
filtering reduce
low
location KHz
recording
partially
masked
with
to
or
the
should
may
be
other
arrives
at
speakers.
then
guarantees
from
the
listener. to
compensate response.
pass
filters
are
the
film be
or
the
on
most
Dropouts use
-17-
ADR to
and of
printing
phasing was
surround with
full
be
mono poor
needed
frequency
system. remove
the
original
may low
mag
errors
in
encoded
unwanted
necessary
judicious
to
speaker
equalization
present
levels.
used
and
and
preserve
microphones
splatter
excessive
it
frequency
rumble
8-10
sibilant
encoders
is
front
the
videodisc,
If
SQ
to
low
track.
buzzing,
at
and
optical
Some
the
for
mags,
delay
is
feeds.
distortion
track
signal
hearing
amplifier
high
signals
equalizers
the
four or
through
amplifier
four
the
A
system
distortion
to bypass
the
matrix
human
for
is Dolby
speakers
from
and
power
Academy
The
inaudible
pass
a soundtrack
used
from
crosstalk
It
surround
surround
of
largely
20).
the
The
signal
effect
acoustics,
the
in
the
outputs
in
soundfield. to
be
films,
be
inherent
after
back
will
to produce
the
equalized
Enhancement
B decoded.
from
amp
(figure
Directional
Dolby
signal
to
mastering
should
and
a head
separation.
precedence
track
inserted
of
to
KHz
decoders
ears
front
fed
to 12.5
SQ
the
is
a Tate
degree
the
When
to
filtered
assure
that
output
Low hiss
pass
or
tracks
due
to
edits
may
be
reverberation.
Videotape
programs
production the
and
horizontal the
prevent
excessive
particles present
in
Interchannel
jitter over
10
flutter,
audio,
harmonic, distortion.
The
analogue
is
a 15
code
on
Tracks Track the
4 track
the
videotape
3 is
to
the
on
track
stereo
prevent
out
to
as
magnetic are
tracks
on
phase
of
more
than
due
to
excessive
wow
and
the
the
audio SMPTE
1/2"
with
programs time
tape.
noise
reduction.
the
time
code
into
are
also
frequently
program.
to
problems
avoid
PCM the
associated
audio
encoded
distortion, with
sources wow
analogue
-18-
and
flutter,
systems.
3-6
difference
quality
via
of
often
reduction.
twin-tone
4 on
to
Saturation is
high
the
Due
noise
errors
program
leakage
often
signigifant
synchronized
and
is
audio
and
for
KHz)
and
of
common.
common,
of
levels
stereo
response
format
tape
2 carry
blank
Synchronized used
tape
IPS
1 and
use
with
are
is
hiss
to
leakage
clipping.
head
the
audio addition
filtered
and
intermodulation,
frequency
ideal
band
levels
notch
between
Frequency
poor In
film,
video
20 degrees
audio
record
be
the
the
(15.734
elevated
shifts
KHz.
of
deviation of
of
television.
mandating
exceed
entire
excessive
must
carrier
phase may
at
the
and
1" videotape,
the
to
frequency
orientation on
videotape
audio
to all
problems
flyback
in
angular
common
distortion
present
the
subject
techniques
noise
video
are
and
other
db
7.
Conclusion
The
NTSC
television
system
a noise-free
picture
with
high
sound.
Our
in
quality
their
efforts
However,
the
to
high
sets
the
The
laser
quality
do
us
a poor
optical
a hope
justice
new
to
so
the
of
programs
of
that
replica
monitors
a
the
usually
videodisc,
era
for
in
ends
interference,
signal
consumer
promises Let
is
are
high
continuing
are
quality supply
-19-
SMPTE high
at
now
of
are
and
assiduous
transmitter.
cheap
television
one
audio
of
becoming
program
color,
define
quality.
original to
to
the
received
the
coupled
medium.
true
and
the of
that
sufficient
resolution,
brothers
quality
problems,
presentation
high
transmit
Transmission degrade
standards
visual
production. the
high
available
presentation.
software
that
will
Bibliograph
IEC
_
Specification
Abbagnaro,
for
Lou:
The
Laservision
CX
Noise
February
Badger,
Greg:
Willcocks,
May
System,
1982
Audio,
1982
in
Reproduction
Systems,
Martin:
S. Patent
Reduction
Advancements
the
Transformations AES
U.
Videodisc,
USQ
Family
AES
of
of Multichannel
Preprint
the
#1779
Energy
(J-4)
Sphere,
Preprint
#3,944,735:
Tate
Directional
Enhancement
System
Acknowledgements
I wish
to
thank
assistance: for
the
The
late
psychoacoustics
Carolyn
Davis
Wolfe
and
Phil
Boole
John
Browne
Rick
of
following C.A.
and
people "Puddie"
monitoring
Syn-Aud-Con;
Montez
and
Jeff
of
PVI.
of Berlin
Brad
Twentieth of
PBRS;
-20-
for
their
Rodgers
and
techniques; Plunkett
of
Chris
and
Chips Don
Century-Fox and
help
Davis
and
Urei;
Dick
Telecommunications; Leister
and
LIST
OF
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16.
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after
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Effect
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Disc
Track
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on
Audio
Signal.
Standard
Maximum
compression
level
where
compression
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14 dB
-40 dB
-28 dB
100 Hz
500 Hz
and
the
2:1
changes
to
1:1 (re 0 VU):
Low
frequency
off
(-3
expander
Figure
17.
filter
dB)
in
LaserDisc CX-14
expansion ratio:
Knee
CX-20
for LP
cut-
compressor/
control
circuit:
Modifications Applications.
to
LP
CX
System
for
LaserDisc
Left
Left Voltage Controlled
In
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AmpLifier v
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Control
r
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,Right Out _
Encoder
Left
Left _n
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Amplifier
Pass
In
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_
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Decoder
Figure
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CX Encoder
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APPENDIX
_"
CX
COMPRESSION
SPECIFICATIONS
FOR
LASERVISION
VIDEODISCS
General To improve the dynamic range of the audio program on the laser optical videodisc, an optional companding technique is recommended. This technique has been developed by the CBS Technology Center and is known as CX. Use of this system for videodisc players or discs is only permitted if a license has been executed with the CBS Technology Center. The version of CX for LaserDisc has been modified from the standard CX for LP's or other videodisc formats, and those CX encoders/decoders will not yield optimum results for LaserDisc. The technique is compatible in that the program, if encoded in the CX format, can be played back on a decoding player or a non-decoding player. If played on a decoding player the fu_l benefit of 14 dB noise reduction will be achieved. Playback on a non-decoding player will be completely satisfactory but will not yield noise reduction improvement. To assure optimum compatibility between disc and player, it is essential that all disc manufacturers encoding discs for the CX process use the same reference level parameters to ensure a specific correspondence between the static compression curve of the encoder and the modulation level of the audio carriers on the videodisc. Similarly, all should arrange characteristic. Encoding 1.
player manufacturers incorporating CX decoders operating levels to match the prescribed disc
Characteristics
Statics
The static encoding characteristic of the CX system, optimized for LaserDisc use is shown in Figure 1. The figure describes the static gain relationship between the input signal level to the encoder, in dB, referenced to standard operating level, and the audio subcarrier modulation in dB re 100% modulation. Note that the modulator gain should be adjusted such that operating level at 1 KHz produces 40% modulation deviation) and at the limit, + 16 dB input will modulation (_100 KHz deviation) _ 0.5 dB.
standard 0 db + 0.5 dB (+ 40 KHz p_oduce 100T
The diagram also indicates that the "knee", the point on the compressor characteristic curve below which a 1:1 gain correspondence exists between input and output, should occur 28 dB + 0.5 dB below standard operating level.
-Al-
8/12/82
2.
Dynamics
To ensure compatibility between encoding and decoding it is also necessary to match the dynamics between compression and subsequent expansion. These parameters are defined with reference to Figure (encoder block diagram) and Figure 3, a simplified circuit diagram of the control portion of the CX system. These parameters are: 1.
Control
2.
Fast
Rectifier
High
3.
Fast
Rectifier Release 10 msec + 5%
4.
Slow
Rectifier
Attack
5.
Slow
Rectifier
Release
6.
Low
7.
Attack
Level
30 8.
Engineering 1.
Pass
Filter
Attack
Integrator
Compensator msec + 5%
(C25,
Time Time
Time Time (C29,
Decay
RS1):
(C27, (C27,
fc
=
500
R100):
=
R99 + R100):
(C29, R105): (C29,
(C28,
=
2
%
5% +
5%
=
= 30 msec
R107):
R106):
Time
Hz
1 msec
+ 5%
= 200 msec sec
R108
+
+
2A
+ 5%
5%
R109) :
In order to ensure proper transitions between different time constant attack and decay times, a fixed relationship should exist between diode forward voltage drops and the audio operating level. This relationship is established by providing the proper control path gain for specific diode types. With the application of a 1 KHz standard operating level signal, the DC control voltage (at TP-1, Figure 2) should be 3.85 + 10% times greater than the forward voltage drop of the diodes CR 12, 13, 14.
Practice
In order channels maintained
to or
prevent overloading of either audio transmission the control voltage, a headroom of 16 dB should above "0" operating level.
be
2.
At no time should the peak modulation level be exceed 150% times (+ 150 KHz). A hard limiter after the preemphas_s network in the mastering accomplish this objective.
allowed to should be used machine to
3.
The purpose of the CX process is to prevent the deterioration of the program noise floor due to noise contributions from the videodisc process. For this to be effective, the signal to noise ratio of material presented to the CX Encoder should be at least 70 dB with CCIR 468-2 and ARM metering.
-A28/12/82
[_'
1.
CX
EXPANSION
SPECIFICATIONS
FOR
LASERVISION
VIDEODISCS
Statics
The static decoding characteristic of the CX system'optimized for videodisc use is shown in Figure 4. The figure describes the static gain relationship between the output of the audio demodulator in dB referenced to the level at 100% modulation and the output of the decoder after deemphasis in dB referenced to standard operating level. Note that the knee, the point at which the decode characteristic switches to linear operation, occurs at an audio demodulator output 22 dB below the 100% modulation reference point (_ 1 dB). 2.
Dynamics
The time constants associated with the circuits which control the dynamics of the decoding process must agree with the time constants employed in the encoding process. These time constant specifications referenced to Figures 2B (the decoder block diagram) and Figure 3 (the CX control logic) are as follows: 1.
Control
High
2.
Fast
Rectifier
3.
Fast
Rectifier Release 10 msec + 15%
4.
Slow
Rectifier
Attack
5.
Slow
Rectifier
Release
6.
Low
7.
Attack Compensator 30 msec + 15%
8.
In order to ensure proper transitions between different time constant attack and decay times, a fixed relationship should exist between diode forward voltage drops and the audio operating level. This relationship is established by providing the proper control path gain for specific diode types. With the application of a 1 kHz standard operating level signal, the DC control voltage (at TP-1, F_gure 2) should be 3.85 + 10% times greater than the forward voltage drop of the diodes CR 12, 13, 14.
Level
Pass
Filter
Attack
Integrator
(C25, R81)
Time Time
Time Time
(C27, R100): (C27, R99
(C29, R107):
Time
(C29,
Hz _ 5%
= 1 msec
+ R100):
(C29, R105):
(C29, R106):
Decay
fc = 500
(+ 15%)
=
= 30 msec
+
= 200 msec
15% + 15%
= 2 sec _ 15% R108
+ R109):
=
-A38/12/82
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Figure 1 Appendix
_-I
CX
o
Static
O
Encoding
Characteristics
e/12/82
Left
Left Voltage
._
Controlled Amplifier In
i
High Pass Filter
e
_a_h V _,
Right In
I Pass High _
Voltage Controlled An_plifier
Figure 2A Appendix
Out
Block Diagram
Right Out
of Encoder
Left Voltage
_-
. Left Controlled
In
I
Pass High Filter ' ']
I
Amplifier
_ Control
Pass
In Right
l
_ I
Filter!
Figure 2B Appendix
Out
Block
Controlled Out A_plifier ;Voltage I Right
DiagramofDecoder
8/12/82
Attack Block Slow
Rectifier R _I
_ I
Attack & Release Block
_
Release
I
Block
I
Block
p
_- Capacitor
Integrator/
Co ntoensator
l
;
Adder
l' Figure 3 Appendix
Block
Diagram
of Control
C
Path
8/12/82
Audio Demodulator Output (dB Re 100% Modulation)
(-8) -40
-30
(-22) -20
-10440%)
0
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0
I
-10 x O_D _o o
o_
__-20
D _
T
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(-28)4 __ 3O
-3O
-4O Figure4, Appendix
CX
Decoding
Gain
Characteristic
8/12/82