Sony BVU-950 - Page 28

HHLR pulse is positive going or not. If it is positive going, then
the
gate
does
nothing.
If
it
is
not
positive
going,
then
the
reason
is because the vertical syne is occurring efter a helf norizontal
line rather than a full line. in this case, the gate emits a negative
going pulse, which triggers the flip-flop to reset the control sicnai
so that it becomes a negative-going pulse. Therefore, the 0 volt
status
of
the
control
signal
indicates
an
odd
field.
The
positive
going pulse on the control sSignai would indicate the start of an even
field, which could be the start of a new frame. This is what we
mean by "framing servo," and should explain how the framing servo
accomplishes the functions we listed above.
So, if we've gone to all this trouble to make a framing servo, then
why do we have a framing servo on/off switch?
Simply stated, it's so that you can use a tape which was recorded on
a machine without a framing servo!
Look at the example below: On &@ tape recorded without a framing
servo, there iS no standard relation between the on/off status of
the control signal pulse, and the even/odd status of the fields.
When editing, you may find that you go from an even field or one
frame to another even field on the first frame of the next scene.
If the framing servo were on when you recorded this kind of edit,
the framing servo would change the-phase of Record CTL resulting in
a poor edit. That's why we have an on/off switch for the framing
servo; to prevent this sort cf bad edit.
Scene C woe Scene B wm Scene A —
EOEOEOEOEOIOEO EO EC
Tape quay
Chart-5
What's the story with "flagging" and "whipping" at edit points?
The duration of one horizontal line is 63.5 microseconds under the
EIA/VNTSC system. In the case of a wrong field edit, this duration
may increase or decrease by 32.25 microseconds, the duration of a half
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