INSTALLATION
page 7
Keys
There are two keyers in the MVS3: Effects (upstream), and DSK (downstream). Each
keyer can be used with any of the six external key inputs (KEY1 thru KEY5 and
CGEN), the optional RGB chromakeyer, as well as with insert bus video as a key input.
The gain of the Effects keyer and the Downstream keyer can be continuously adjusted
from high-gain to linear by use of the appropriate key gain commands. The Effects keyer
and the DSK keyer will accept 1v standard monochrome key signals.
Two different types of key signals are accepted by the MVS3, high-gain and linear keys.
HIGH-GAIN
KEY
This is the conventional key signal, which has been in use for
many years. An example is the use of a monochrome camera
focused on an art card, with the art traditionally being composed
of white letters on a black background. This polarity is less
sensitive to camera and lens signal falloff at picture edges and
corners. For this use, the signal is nominally 1v p-p, but in
practice a keyer gain of ten or more is used to clean up
imperfections in the black and white areas. This means that the
middle ten percent or so of the camera signal is amplified and
used to dissolve from background to insert bus.
LINEAR
KEY
Electronically generated key signals from equipment such as
character generators and digital effects generators usually
require a "linear" keyer. The linear keyer has a gain of 1, so a
full one volt level will dissolve to the insert bus and a black level
will select the background picture. If a high gain keyer is used
instead, the key edges will be too hard and cause chroma crawl.
Also, if a transparent key is used it will not be reproduced
correctly. The Effects keyer can be made linear by pushing the
effects KEY GAIN button and using the +/- keys to set the
desired softness. The DSK key is similarly adjusted using the
DSK KEY GAIN button.
Key Delay
The MVS switcher has a very short overall path delay thru the mixer. Worst case path
matching inaccuracies are typically less than 35 ns.
