Frame Rate Lock Setting; Vertical Interval Data - Videonics MX-1 Instruction Manual

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Frame Rate Lock Setting

There is one option you can set that affects the operation of the MX-1's
TBC. The option, frame rate lock disable, reduces or eliminates the need for
dropped or duplicated video fields, a common consequence of TBC use. The
option is normally set to 0 to enable locking and you will not need to change
it unless you are using equipment that demands an unusually accurate time
base. The following section describes it in detail.
What is Frame Rate Locking?
A TBC forces the video output to an exact rate, independent of the frame
rate of the input signals. If the input video is coming at a slightly slower rate,
there will come an instant when the output gets ahead of the input and a
video field will have to be repeated. Conversely, if the input is running
slightly faster than the output, eventually a field has to be dropped. The
visible result is a small hesitation or gap in the action and a vertical jump in
the picture, at rare intervals. This is an inherent, unavoidable artifact of TBC
operation. In most cases, the rates are very close and frame drops and
duplication are very rare (hours apart) and unobtrusive.
The MX-1's automatically compensates for this. It adjusts the frame rate of
the output by very small amounts at the end of each video field, to reduce
differences between the input and output rates. This reduces or eliminates
the need to drop or duplicate fields. However, it does mean that deviations in
input frame rates will cause the output frame rate to be very slightly off-
standard.
This slight change in frame rate is of no consequence in most setups and
we recommend you leave the setting off (0, its normal setting). If you are
connected to equipment that requires very exact frame rates, you can change
the setting to 1 and the timing of the output will be more exact and fields will
be dropped or duplicated as required.
Note that in real life situations, neither setting will result in serious picture
problems unless the timing of the input video is beyond accepted standards.
How to Turn Frame Rate Locking On and Off
To change the Frame Lock Disable Setting, press SHIFT and SETUP at the
same time to enter Advanced Setup mode (Chapter 5, "Setup Screen") and
change the setting. "1" disables locking and "0" turns locking back on.

Vertical Interval Data

Time code, closed captioning, and other data in the vertical interval should
be added after mixing (downstream from the MX-1) since dissolves and other
transitions would mix the data signals, making them unreadable. Depending
on how data has been added and the accuracy of a source's time base, vertical
interval data in the sources may be removed by the TBC.
VIDEONICS DIGITAL VIDEO MIXER