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Technical Information; Basic T Erminology - Sony PCM-F1 Operating Instructions Manual

Sony pcm-f1 digital audio processor
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TECHNICAL
INFORMATION
BASIC
TERMI NOLOGY
A/
0
and
D/A
converters
In
a
PCM
system,
analog
s
ignals are quantized and then recorded
as digi
tal
signals. In reproduction, the digital
signals
are
converted
back
into
analog
signals.
Converting the signals
into
digital
signals
is performed
by
the
analog-to-digital
(A/D) converter,
and
convert-
ing the
digital
signals
into analog signals is
performed
by the
digital-to-analog (D/A)
converter.
A
nalog
The wo rd
analog
is used in cont rast to
digital.
Analog quant ities
denote
quantit ies that change continuously like the
temperature or
voltages.
Ordinary
audio
signa
ls
are
called
analog signals, and
VU
meters have an
"analogy"
wit
h the
variat
ion in these analog
signals
which is
indicated
by the deflection
of
the
pointer.
This type
of
meter
can
be
called
an analog display
meter.
Bit
This is
an abbreviation
of
binary
digit. It
is
a unit
of
information
equal
to one binary
decision,
so
that
1 digit is
referred
to
as
1
bit.
Three bits
refer to a 3-digit code. With n
bits,
it
is possible
to
in-
dicate
and subdivide 2n
types of information.
Code error
This refers
to an erroneous
1
or
0 in the encoded
signals.
It is
caus-
ed
by
dropouts,
jitter,
noise, etc. If a recording is played back with
these
code errors,
It will
come
t hrough as a c licking
sound.
In order
to
compensate for
these errors, a number
of
methods
are
used in
t
he ci rcu
itry: pre-value
holding,
linea
r
interpo
lat
ion and
error cor-
rection word
encod
ing.
CRCC
(Cycl ic Redundancy
Check Code)
A group of bits or a "word"
which detects
erroneous
data.
The prob-
ability of detecting erroneous
data depends upon the
number of
bits.
In the
EIAJ
format
and
the PCM-F1
,
each
TV
H
(horizontal) line
has
one
"word"
of CRCC which comprises
16
bits, so erroneous
data are detected at
a
99.9985%
probability.
Digital
Th
is word originates
from
"d igit"
meaning
finger and is
used in
contrast
to
analog. A
digital
quan tity
denotes a quantity by
which a
variable amount is
discontinuous ly encoded (numerical va
lues). In
other words, a
digital
quan
tity is an encoded
analog q
uantity. The
word
also denotes
using numbers
expressed
in digits
and
in
a cer-
tain
scale of
notation
to represent
all
the variables that
occur in a
problem
.
Dropout
This
refers to
dist
inct bu
t
temporary gaps
in
t
he signal
level
during
the playback
of
recorded data
caused
by marks
or dirt on
the
sur-
face of the
tape.
In PCM
systems,
it results
direct
ly in a
code error.
When burst-formation type
of
dropout
s
occur, the
errors are scat·
tered
and corrected or
int
erpolated.
Dynamic range
In PCM, dynamic range
is
expressed as the ratio between the
max-
imum
accept
able
signal input and the quantizing noise. W ith linear
quantizing
t
he range is
proport
ional to t
he
number
of bits,
but with
non-linear quantizing
the
obtai
nable
dynamic
range is m
uch
wider
wi th the
same
number of bits.
Thus,
in the PCM-F1
which
has
adopted linear
quantization
fo
rmat
, the dynamic range
of
the
16-bit
format is
wider
than th
at of the 14-bit format.
24
Encoding
Encoding denotes the
conversion of
quantized amplitudes into a
pulse
code. A binary
code is
most
commonly used.
In actual opera-
tion,
t
he quantizing and
encoding
are performed simultaneously
by
the analog-to-digital
converter.
Error
c
orrection word
s
In the 14-bit
format of
the
EIAJ,
two
error correction
"words",
P and
Q,
are added to each
dat
a
block consisting of six
"
words".
Each
P
and
Q
corrects o ne
"
word" of
erroneous
data, so that two
"
words"
of erron eous data
in
a
dat
a
block can
be
correct
ed. W
it
h the in-
te rleaving process, erroneous data up
to 32
H
can be
corrected
.
Interleaving
Interleaving is a
method to
disperse dropout
errors
by
changing
the
sequence
of
information
"words"
(hereafter referred
to
simply as
word
without quotation marks)
in
recording.
Restored to
the
original
order in
playback,
the
erroneous
word is
invariably
placed
between the
correct
words,
and
thus linear
interpolation,
etc.,
can
be
easily
performed.
Jitter
This
term
denotes the
instabili
ty
of
a signal in either
its ampl itude,
its phase,
or
both. It
is
generated
when signals are
played back
on
a
t
ape
recorder with
wow
and
flutter,
whereby
noise
is
added
to
t
he
signals. In PCM systems,
it
is
the
cause
of
code
errors along
with
dropouts in the
tape
medium.
Linear interpolation
When a word erro
r
has been
detected
,
it
is corrected by the
error
correction
c ircu itry.
If the
error exceeds
the error
correct
ion
capabi
lity of the digital audio processor,
t
he
average
valu
e of the
preced ing and
succeed ing
words
is substituted
for
the
erroneous
word.
The
error
is
thus
interpolated
so that there
is
no audible dif·
ference.
In the
14-bit
format of
the
EIAJ, burst errors
of 32H
or
more,
which cannot be corrected, are
interpolated.
PCM
This
acronym stands
for pulse
code
modulation.
It refers to
a
system of
modu lation
whereby ordinary signals like
audio signals
are replaced
by
pulses,
their amplitudes are turned into
digital
codes,
and the
resul
ting
signals are transmitted or
recorded. All the
signals are
expressed in
binary digits,
1
for every
pulse and
0
for
every
absence
of pulse.
Therefore,
the signals are resistant to
noise,
and distortion
can be
kept down
to a
very
low level right up
to
t he
high
frequencies
wit
hout
being
dependent
on
t
he
f
requency.
In the
PCM
system,
the s ignals
are
sampled
severa
l
ten
thousands
t
imes a
secon
d and the
sampl
ed values
are
quantized.
The code
resulted
from
qu
antization
each time
is 42
bits
consisti
ng of 14 bits
for
ri
ght
(R)
channel,
14
bit
s
for
left
(L)
channel and
14
bits
for
error
correct ion and
error
detect
ion
.
The
binary
code
per
second is
equivalent to a frequency
of
several
megahertz.
A frequency as high as this
cannot be
recorded by a
convent
ional
audio tape
recorder.
This is why
a video
cassette
recorder,
wh ich
can
record the PCM
code
delivered by the PCM dig ital audio
proc-
essor,
is required to
be used with
the PCM
processor.
The PCM
processor
requi
res less
than
half
the
frequency
bandwidt
h
of TV
signals.
Of
course,
to
be recorded on a
video
cassette recorder,
the
PCM
code
must f irst be
converted into a
TV
signal.

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