ABOUT CLOCK
The clock pulse is keyed either to specified frames in the ordinary (continuous) modes
or to the beginning of the
recording of video
in the time-lapse recording modes
Output signals can be used to synchronize the VCR
other equipment, such as sequential switchers. These signals are
generated just after the VCR begins to record either fields or frames of video. in the
ordinary recording
is
done in the frame mode, while in timelapse operation
only one
is recorded at each time-lapse interval.
in
real-time playback, a frame consists of two interlaced fields of video, and in
recorders, each field of a
frame
of video is processed as part of a frame. During playback in one of the time-lapse modes
96H modes), a
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
The
pulse output has great versatility. if the clock output mode is set to 1 and the VCR is set to the 3H or
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
after the recording of each video field. The time-lapse modes are named relative to the
real-time duration of a standard
VHS E-180 cassette on LP mode. For instance, if the Ll &hour time-lapse mode is selected, it means that a
cassette will
last 18 hours. The ratio 18
hours 3 shows that one field of video will be recorded in the
8H mode for every 3 fields in
the
ordinary mode. Since the normal field rate is 60 fields/second, the time elapsed between recorded fields in the
hour mode is:
18 hours
6 hours
X
0.06
in the
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
and the ratios available are
10,
and
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
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
mode, we saw that a field of
video is recorded every 0.06 second. If we select an FDR of 3, then the
pulse will be generated shortly
after every third
recorded field, or
0.06
field
X
0.180
In the
recording mode, then, if an FDR of 3 is selected. the clock pulse will be generated every 0.180 second.
The clock pulse frequency can be selected as follows:
Desired Frequency
Number to Select
of Pulse
from Screen Display
Every frame*
1
Every second frame
2
Every third frame
3
Every fourth frame
4
Every fifth frame
5
Every tenth frame
1 0
Every 15th frame
1 5
Every 20th frame
2 0
Every 25th frame
2 5
Every 30th frame
3 0
Every 50th frame
5 0
Every 60th’frame
6 0
l
When the clock pulse is keyed to one of the ordinary recording modes
it is generated just after the recording of a
frame; when it is keyed to a time-lapse mode
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
(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 50 times per second.