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Quantizing and quantizing noise
Quantizing refers
to
the process whereby
the range
of
values
of
the
sampled ampl
itude
of an analog signal is divided
into
a
finite
number
of
subranges,
each
represented by
an assigned (quantized)
value, and substituted for the
digital
sig
nals.
There is a slight error
between
the original signal
and the quantized
value.
This is heard
as noise
and is known
as
quantizing noise,
or
quantizat
ion
distor-
tion.
Th
is
noise is inherent
in principle to
PCM.
The
signal-to-noise
ratio
of the
PCM
and
dynamic range
are determined
by
th is noise.
Sampling
and holding
This
is
a circu
it wh
ich is
used in
an ana
log-to-digital
converter to
measure an analog signal (sampling) and
to
increase
the duration
of that signal (holding). With
holding,
a
fixed
period of
t
ime
is
re-
q
uired to convert
the
analog signal into a
digital
signal.
Sampling
and sampling theorem
Sampling
refers to
the extraction of the amplitude of an analog
signal
at regular intervals of
time.
The sampling theorem (developed
by
Shannon) states
that
two
samples per
cycle
wil
l
completely
characterize
a bandlimited
s ignal;
that
is,
the
sampling rate must be twice the
highest frequen-
cy
component.
Word
A group of bits that express a single
quantizing
value
is
called a
word. In
the PCM-F1
,
a word comprises 14 or 16 bits.
SYSTEM
AND CIRCUIT DESCRIPTION
Emphasis
The
emphasis circuit of
this
unit is designed to
reduce
the amount
of noise and improve the signa
l-to-noise ratio
by automatically
boost
ing
the high-frequency response during recording
(pre·
emphasis) and detecting the boosted amount and lowering
the
response during
playback
(de-emphasis).
LED peak
program meters
A
n incoming analog signal
is
converted to a digital
signal,
which
is
further converted to a video signal and delivered
from
the VIDEO
OUT jack of this unit to a video input jack of a video cassette
recorder. When
the
video cassette recorder is set
to the record
or
record
monitoring mode,
the video
output
signal from
the
recorder
is
fed to the
VIDEO IN
jack of this
unit. The
incoming video signal
is
converted
to
a
digital
signal, then
to
an analog
signal,
and the
peaks of this analog signal are displayed on the
LED peak
program
meters.
For
this reason
,
if the VIDEO IN jack
of
this unit is not
connected
with
the
video output jack of the video cassette
recorder
even in
recording, you cannot monitor the input signals to
be
recorded,
nor
do
the meters deflect,
though recordings
can
be
made.
14-bit format and 16-blt format
The 14-bit format of the PCM-F1
conforms
to the technical
specifi-
cations of the
EIAJ
which has adopted the
14-bit linear
quantiza-
tion
format
.
In the PCM-F1
,
the 16-bit format which is compatible
with the
14-bit format
of the
EIAJ is adopted
together with
the
14-bit
format
in
order
to
obtain
better
results such as wider
dynamic
range and
less
distortion.
The 14-bit and 16-bit formats
can
be
selected with
the RES
selector.
A tape
recorded
using the
PCM-F1
with
the RES
selector set to "16
BIT"
can
be
played back
using
another
PCM digital
audio proc-
essor
which
conforms
to the 14-bit format
of the
EIAJ
.
In this
case,
the
reproduction will
be
equivalent to that of the
14-bit format.
A
tape
recorded
using
another
PCM digital
audio processor which
conforms to
the
14-bit
format
of
the EIAJ
can, of course,
be played
back using t
his
unit.
Duri ng playback, the
difference
between these two formats is
detected automat
ically.
If a tape recorded
in
accordance with the 16-bit format
is
duplicated
using
the
digital-to-digital
tape copy function of
this
unit
with the
RES
selector set
to
"
14 BIT", the format
will be
con-
verted
to the 14-bit format.
Error correction capability of the 14-bit'and 16-bit
format
s
In recording
with the 16-bit format of
this
unit,
the
error correction
word
Q
of the 14-bit format is rep
laced
by
t
he
15th
and 16th
bits of
the data
so
that the
16-bit
format is
compatible wit
h
the 14-bit
for-
mat of the
EIAJ.
For
convenience
sake,
we express the word com-
prising
the
information
of
the 15th
and
16th
bits
by
a symbol
"
S" in-
stead of
the
symbol
"Q"
of
the
14-bit format.
In
the 14-bit format,
data contain error correction words of
P
and Q; in
the 16-bit
format,
data contain a
single
error correction word of
P. Accordingly,
the
error correction capability of the 16-bit
format
is
inferior
to
that of
t he
14-bit format. If
a tape
recorded
with the 16-bit format is played
back
by
using
a
PCM
digital
audio
processor which conforms to
the
14-bit
format of the
EIAJ,
the error correction capability wil
l
be
equal to one parity bit of the 16-bit
format.
Usable error correction
Error correction
word
capability
14-bit format
Two
parit
y bits of
Burst
errors of
up
to
of the
EIAJ
P and Q
32
H
can be corrected
.
16-bit
format
A s
ing
le parity
bit
of
P
Burst
errors of up to
of
the PCM-F1
16 H
can
be
corrected
.
It
should be
noted that
burst errors
beyond
the error correction
capability will be compensated for so that
they
are not perceptib le.
25
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