Grass Valley Switcher Products - Manual (Page 11)

Switcher Products — Protocols Manual11
Tally Background Information
Tally Types
Tally requirements can go beyond simple on/off air indication for each
source. This section describes the types of tally information which can be
provided via the switcher tally relays or the serial protocol.
The switcher performs five tally calculations: on-air tally, plus four other
customer specified calculations. Each calculation may be customized by
selecting the tally type and which buses contribute to the tally.
There are three basic types of tally calculations and two specific derivatives
for the “output tally” type.
Output Tally
Output tally indicates which sources contribute to a specific output or
group of outputs (maximum of four outputs). On-air and look-ahead tally
are specific cases of output tally.
Output tally needs a starting point for tally calculations. The customer can
select one or more outputs which will be included in the tally calculation.
Any sources which appear on those outputs will be tallied.
On-air Tally
On-air tally indicates whether a source is on or off air. This information is
most often used to provide camera tally so the camera operator and the
talent know when the camera is included on the program output(s) of the
production switcher. It is a special case of output tally. It is provided as a
separate type to ease tally configuration.
The switcher has more than one output which may be on air (e.g., all four
program outputs of the PGM PST bank may have different source contribu-
tions). On air tally includes sources which contribute to any of these out-
puts. On-air tally had no configuration. It tallies any source which
contributes to any of the four PGM PST program outputs.
Look-ahead Tally
Look-ahead tally is similar to On-air tally but is based on the selection
made on the switcher’s main PRESET bus. It is intended to indicate which
sources will be on air if a program-preset transition is performed. Look-
ahead tally is also a special case of output tally. It is provided as a separate
type to ease tally configuration. Look-ahead tally has no configuration. It
tallies any source which contributes to the look-ahead state for any of the
four program outputs of the PGM PST bank.