JVC SR-W320U User Manual

11 APPENDIX
Technical Guide
W-VHS-related technologies
W-VHS is the next-generation format compatible with
HDTV while taking advantage of the technical assets
of VHS. W-VHS provides three modes: HD (High-
Definition) mode capable of recording and playback
high vision signals; SD (Standard Definition) mode for
recording the existing TV signals with a high picture
quality ; and SD2 mode capable of recording the
existing TV signal in two separate, parallel lines,
which will find interesting applications in future. This
machine is compatible with two of these three modes,
HD and SD modes.
@ High-quality video heads (HD/SD/S-VHS/VHS)
Picture quality of a video cassette recorder depends
on video heads. The SR-W320U is equipped with
specially developed high-quality heads separately for
HD/SD and S-VHS/VHS modes.
Sendust HD Pro-head (HD/SD)
Since W-VHS uses a metal tape, a greater quantity of
information must be transmitted between the tape
and the head than with S-VHS/VHS, resulting in
severe demand imposed on the head.
Sendust Pro Head is made of Sendust alloy, not only
at the gap section but also over the entire magnetic
path. This has achieved superb recording
characteristics throughout the whole range from low
to higher frequencies, while suppressing noise during
playback.
In HD mode, two heads must be always in contact
with the tape because 2 channel parallel recording is
executed. Since the tape is wound around only half
the circumference of the rotary drum supporting the
head, four Sendust HD Pro heads are place in two
pairs, opposite to each other at an angle of 180° over
the rotary drum.
Super Crystal Pro head (S-VHS/VHS standard mode)
A pair of heads are used for recording and playback
of video signals. The track width has been made
different between the two heads to ensure a high
picture quality even during special playback such as
search. Super Crystal Pro heads have track widths
optimumly selected for excellent picture quality, which
are in good balance with each other with minimum
interference from the neighboring track. The
narrower track is now 17% wider than before. All this
has led to well-balanced head characteristics and
therefore to further enhanced picture quality.
B® HD baseband recording
In W-VHS, high-vision signals are recorded and
played back with component baseband signals,
without using the method of improving resolution by
means of bandwidth compression such as MUSE.
Since the signals input are thus recorded and played
back as they are, the resultant picture is free from
the signal format restrictions and appears quite
natural with no “bias” associated with compression.
@® W-VHS high-performance metal tape
In order to ensure high picture quality of high vision
signats on baseband, it is necessary to record signals
with a wider frequency range on the tape. To this
end, W-VHS uses a newly developed metal tape
whose high-range characteristics are 8 dB or more
better than in conventional tapes. This metal tape
enables you to enjoy high vision pictures with
enhanced quality for a prolonged period, using the
cassette as small as the conventional-format tapes.
@ Two-track parallel recording
Since high vision signals are packed with the quantity
of information four or five times greater than existing
TV signals, it is difficult to ensure necessary technical
resources merely by development of a single
technical element such as introducing a high-
performance tape.
W-VHS HD mode has resolved this problem by
developing and establishing a challenging method: to
handle this immense quantity of information, a high-
vision signal is divided into two parts by digital signal
processing, the two parts then being recorded and
played back using two video signal tracks together.
In playback, the two signals from separate tracks are
combined together to rebuild the original high vision
signal. That is, there is no loss of information during
high vision recording on the tape.
® Vertical emphasis
There are a number of technical approaches to
reduce noise. The simpler and easier one of those
approaches is cut out smail signals by regarding
them simply as noise. This could not be a good idea
because the picture is deprived of detailed
components of video signal.
The idea of “emphasis” is able to reduce noise
without such by-product based on the principle that
video signals are “emphasized” during recording to
compensate for the small signal components to be
lost during playback.
This principle is advantageous in that recording and
playback work complementary to each other so that
only noise can be reduced without cutting off detailed
signal components. VHS and S-VHS have
conventionally used this emphasis technology as
applied to horizontal signa! processing, for instance
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11 APPENDIX
Technical Guide :
as main emphasis and sub emphasis. This method is
now applied to vertical processing to provide the
“vertical emphasis” noise reduction system. With
this, we are one step closer to the ideal of noise
reduction, without loss of detailed signal components.
@ Temporal emphasis
Another noise reduction technology developed for W-
VHS is this temporal emphasis which also
suppresses noise without cutting off detailed signal
components. Temporal emphasis has been invented
by expanding the concept of emphasis in temporal
direction. Emphasis based on the video signal
variation from one frame to another is applied to all
the picture elements of the whole frame by means of
digital signal processing.
Temporal noise reduction which has conventionally
been executed during playback tends to produce an
unnatural effect in terms of motion. A variety of
technical considerations have been made to minimize
this by product. This problem is basically resolved by
the temporal emphasis by virtue of the complement-
ary operation of recording and playback. In view of
this, temporal emphasis obviously plays an important
role in the technical requirement for making noise
reduction in W-VHS compatible with reproduction of
details.
®@ TCI (Time Compress Integration) recording system
Existing TV signal consists of a luminance signal
indicative of brightness and a composite signal
carrying color signals in superposition. Luminance
signal and color signals must be once separated for
different signal processing. They are finally combined
together on the tape as frequency-modulated
luminance signal and color signals frequency-
converted to low range. While of course the
frequencies in use are different between these
signals, recording a luminance signal and color signal
together has caused a number of technical problems
such as interference between signals.
In the high vision system, on the other hand, the
broadcasting station itself transmits luminance signal
and color difference signal separately as different
components. The TCI system has been developed to
take advantage of this principle of high vision.
In the TCI system, the luminance signal and the color
carrying color difference signal are temporally
compressed and rearranged and are then recorded
on the tape. That is, the juminance signal and color
signal are not recorded together, and instead, they
are recorded on different sections of the tape,
minimizing the signal interference in its own principle.
This system is used not only for HD mode for high
vision recoding but also for SD mode for recording
the existing TV signal.
H HD digital TBC (Time Base Corrector)
W-VHS HD mode achieves a high-density recording
using the two-track parallel recording system in which
a high vision signal is recorded in two parallel tracks.
Such two-track system has been associated with one
problem, that is, temporal difference between track
widths during playback, or so-called inter-track jitter.
The time base corrector corrects this jitter and
reinstates the original signal to provide a stable
picture quality.
@ SD digital TBC (Time Base Corrector)
in SD mode, video signal is recorded in one track.
However, as in conventional VHS and S-VHS, jitter is
experienced because of subtle difference in relative
head speed between recording and playback. In
order to offer excellent recording and playback
properties, the SD digital TBC is provided also for SD
mode so that digital signal processing prevent
temporal variation as a cause of jitter of the picture.

JVC SR-W320U Specifications

General

Brand	JVC
Model	SR-W320U
Category	Cassette Player
Language	English