User Bits
Unassigned bits within the 80-bit SMPTE time code
format that may be used for the information such
as the date, scene, or take number. A limited group
of letters (A-F) and the numbers (0-9) are available
to code eight characters of useful information.
A user bit generator, which is often built into
modern TCGs, must be used to enter this special
data, and special time code readers are required
to read this information.
VCR (Video
Cassette Recorder)
An electro-mechanical device used to record and
reproduce video and audio signals in a helical
scan fashion. The videotape is enclosed within
a plastic cartridge or cassette. A threading system
in the tape transport mechanism withdraws the
tape from the cassette and wraps the tape around
numerous guides, the erase head, scanner drum,
audio head, and drive capstan. When the eject
button is pressed, the threading mechanism unwraps
the tape from the transport and winds it back
into the cassette. topˆ
Vectorscope
An instrument used to setup color encoders and
to confirm the proper transmission and/or recording
of color signal. A CRT displays the color subcarrier
in a circular pattern. The graticule contains
a pattern of measuring boxes in positions based
on the hue and chroma characteristics of the color
bar signal. The individual bars appear as bright
dots which should fall within the small boxes
if the color signal has been correctly encoded
and has not been altered in transmission or recording.
The angular position of the color vector indicates
the hue (phase) of the color. The length of the
vector is a measure of the saturation. The color
burst reference marker, a horizontal bar situated
at the 9 o’clock position on the graticule,
is the established reference with respect to the
six colors positioned in their respective boxes.
Since luminance and chroma are
often processed separately in television equipment,
it is necessary to check at various stages to
make sure that the color signal integrity is not
compromised. Color bars are usually recorded on
the head of every reel, preferably from the originating
studio or camera. Unless otherwise instructed,
these bars should be used as a reference to make
any necessary adjustments (video levels, saturation,
phase) on the videotape player. The phase (hue)
adjustment rotates the entire pattern. The saturation
(chroma) adjustment moves the dots inward or outward
to fit into the calibration boxes. Any subsequent
changes, based on the appearance of program material
viewed on a color monitor, should be undertaken
with caution. There should be an understanding
with the customer as to whether the operator is
expected to make gross color corrections on program
material, or whether the head end color bars are
to be considered the absolute reference.
Note that one color cannot be
changed without affecting the others. True color
correction is best done while video is in R-G-B-or
component form. During operation, the vectorscope
can be used to observe excessive chroma levels.
A vectorscope and a waveform monitor are sometimes
combined in a single unit with a single screen
and a switchable graticule. topˆ
Video
Communication medium that electronically transmits
images and sounds. May use magnetic tape as a
recording method.
The visual, or picture, component of an electronically
based communication medium. This includes the
black and white part of the electronic signal,
color information, and synchronizing signals.
Video Cassette
A precision plastic container
that holds prepackaged lengths of videotape that
may be inserted into a VCR. The most popular sizes
of cassettes store tape in 1/4 inch, 1/2 inch
and 3/4 inch widths in lengths from 5 minutes
to 90 minutes. topˆ
Videotape
A long narrow strip of Mylar film coated with
a material capable of being magnetized in uniform
matter and holding these magnetic patterns for
an indefinite period of time. This tape is designed
to record and play back continuous visual images
as well as aural components. Tape widths vary
from 8mm to 2 inches. topˆ
VITC
(Vertical Interval Time Code)
Also called VITC. Time code that is recorded on
two lines of the vertical blanking period in the
video signal. Unlike time code recorded on a longitudinal
linear audio channel, VITC time code is scanned
by the video head even when in still frame. This
time code then is converted to a readable time
code that maybe used to frame accurately, locate,
and define edit points. topˆ
VTR
Videotape Recorder. An electro-mechanical device
designed to record and playback video and audio
signals on magnetic tape wound on open reels.
The tape must be threaded carefully by hand through
the transport and attached to a take-up reel.
topˆ
Waveform
Monitor
A display device that shows the electronic pattern
of the video signal on the face of a Cathode Ray
Tube (CRT). Superimposed on the screen is a scale
vertically divided into 140 divisions, termed
I.R.E. units. The synchronizing pulses occupy
the range between -40 and 0. The video waveform
starts at 0 with black at 7.5 and white at 100.
A waveform monitor is a very necessary and useful
tool to allow the operator to accurately adjust
and monitor video signals. If video levels are
recorded on a videotape improperly; that is, either
too high or too low, it may be impossible to correct
them once they have been copied to another tape.
A WFM allows the operator to view the video signal
and make the appropriate adjustments as necessary
to keep the video signal within prescribed limits.
It is also used to measure sync signal parameters
to be sure that they conform to accepted standards.
Common test signals such as color bars, multi-burst,
staircase and window can easily be evaluated to
determine the performance of an incoming source
or the playback of a recorder. topˆ
Window
Dub
A copy of original videotape with the eight-digit
time code displayed in a rectangular area generally
at the bottom of the screen. This window area
may be surrounded by a black box so that the time
code numbers stand out against a light background.
The window dub is used only as a viewing copy
or may be used as a work copy tape to edit with
since the numbers once recorded in the picture
cannot be removed. topˆ
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