27
Installation
Reference page
About clock pulse
The clock pulse is keyed either to specified frames in continuous
modes (6H or 8H) or to the beginning of the recording of video
fields in the time-lapse recording modes (L18H-224H).
Output signals can be used to synchronize the VCR with other
equipment, such as sequential switchers. These signals are
generated just after the VCR begins to record either fields or
frames of video. In VCR596 or VCR407, continuous recording
(6H or 8H) is done in the frame mode, while in time-lapse
operation (L18H-224H), only one-field is recorded at each time-
lapse interval. In real-time playback, a frame consists of two
interlaced fields of video, and in VHS-compatible recorders, each
field of a single frame of video is processed as part of a frame.
During playback in one of the time-lapse modes (L18H-224H), a
single recorded field is read twice from the tape to produce a
complete video image. This has the effect of reducing the vertical
resolution to one-half its normal value.
The clock pulse output has great versatility. If the clock pulse
output mode is set to 1 and the VCR is set to the 6H or 8H mode,
the clock pulse will be timed for a frequency of 30 Hz. If the VCR
is operating in a time-lapse mode, the clock pulse will occur
slightly after the recording of each video field. The time-lapse
modes are named relative to the 6-hour real-time duration of a
standard VHS T-120 cassette on EP mode. For instance, if the
L18H time-lapse mode is selected, it means that a 6-hour
cassette will also last 18 hours. The ratio 18 hours/6 hours = 3
shows that one field of video will be recorded in the L18H mode
for every 3 fields in the 6H ordinary mode. Since the normal field
rate is 60 fields/second, the time elapsed between recorded fields
in the L18H mode is:
In VCR596 or VCR407, the clock pulse may be selected to be
output every time a field is recorded, or once every two fields, or
every three fields, etc. This number is called the frequency
division ratio (FDR), and the ratios available are 1, 2, 3, 4, 5, 10,
15, 20, 25, 30, 50 and 60, along with a “field” rate, to be explained
below. If the frequency division ratio of 1 is selected, then the
clock pulse will be generated shortly after each recorded frame
(in one of the continuous modes) or each recorded field, if the
VCR is set to a time-lapse mode. If an FDR of 2 is selected, then
a clock pulse will be generated for every second frame or field.
An FDR of 3 will produce a pulse for every third frame or field, etc.
In our example of operation in the L18H mode, we saw that a field
of video is recorded every 0.05 second. If we select an FDR of 3,
then the clock pulse will be generated shortly after every third
recorded field, or
In the L18H recording mode, then, if an FDR of 3 is selected, the
clock pulse will be generated every 0.15 second.
18 hours
6 hours
1 sec
60 fields
0.05 sec
x
=
0.05 sec
1 field
3 fields
0.15 sec
x
=
Desired Frequency
of Pulse
Every frame*
Every second frame
Every third frame
Every fourth frame
Every fifth frame
Every tenth frame
Every 15th frame
Every 20th frame
Every 25th frame
Every 30th frame
Every 50th frame
Every 60th frame
Number to Select
from Screen Display
1
2
3
4
5
10
15
20
25
30
50
60
The clock pulse frequency can be selected as follows:
*
When the clock pulse is keyed to one of the continuous
recording modes (6H or 8H), it is generated just after the
recording of a frame; when it is keyed to a time-lapse mode
(L18H-224H), it is generated just after the field that is about to
be recorded.
One additional option is available in the frequency division ratio
selection. If the word “F” (field) is selected in the screen display
instead of one of the numbers from 1 to 60, then the clock pulse
will be generated each time a field is about to be recorded in one
of the continuous modes, or 60 times per second.
Summary of Contents for VCR407
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