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138 Handbook of Intercom Systems Engineering
and Zeus™ intercom systems, you can also control intercom events from external switches. For
example: you can activate key assignments, close or open crosspoints, activate GPI outputs, etc.
In CS9000 Series intercom systems, general purpose control outputs are provided by optional
FR9528 Relay Frames (8 relays each). In those systems, a relay may be assigned to an intercom
key on a keypanel using the Relay key assignment type. Pressing the intercom key activates the
relay. ADAM™, ADAM™ CS, and Zeus™ intercom systems all have a dedicated GPIO
connector (J27 on a Zeus™ Frame, J903 on an ADAM™ CS Frame, and J11 on the XCP-
ADAM™-MC Master Controller Breakout Panel in an ADAM™ Intercom System). This
connector supports 8 control inputs and 8 control outputs. Additionally, one or more UIO-256
Universal Input/Output frames may be connected to the intercom system. Each UIO-256 provides
another 16 control inputs and 16 control outputs. Control outputs may be assigned to intercom
keys using the Relay key assignment type, and the intercom keys can then control external
devices the same as the FR9528. Control inputs can be assigned to activate “virtual” key
assignments. (A virtual key assignment is a key assignment at an intercom port where there is not
actually any keypanel connected. Basically, you use an external switch to act like a talk or listen
key.) The control inputs and outputs can also be used as conditions for UPL statements in
AZ™EDIT.Finally, there is a GPIO option available for the KP-12 keypanel, and a connector
module option for the KP-32, which includes GPIO. These are referred to as “Local” GPIO, since
they are assigned and used locally at the keypanel. Each local GPIO includes 4 control inputs and
4 control outputs.
Green Room
A room for performers / talent to stay just before making their appearance on stage. This room is
usually close to the stage, and has amenities plus a video and audio monitor.
Ground
The term ground has several meanings. One meaning is a circuit common point potential. Another
meaning is a 0 volts point. Another meaning is a connection to the earth. Another meaning is the
chassis of radio equipment. Radio Frequency engineers almost always connect circuit return to
the chassis. This can cause a ground loop in systems if the chassis is connected to earth ground as
well, and the circuit return in the system encounters another earth ground. The TW system circuit
return is bypassed to earth ground and tied to earth ground through a 10,000 or 22,000 ohm
resistor, in order to prevent ground noises or hums from being introduced into the intercom
system. Connection of a chassis grounded device to the TW System should be done through an
audio isolation transformer.
Ground Loop
A ground loop occurs when a system circuit common is tied to earth ground or another ground or
another conductor at two places in the system. This allows “ground currents” to be superimposed
on the intercom system circuit common, causing hum and spurious noises.
Ground
Potential
Often the potential of the earth, but also the potential at a zero voltage point in a system or an
electrical/electronic circuit.
H
Half Duplex
Half Duplex communication allows two-way conversations, one-way at a time, such that one
person cannot interrupt the other. In data communications, half duplex means sent data is not
confirmable by the receiving end on a continuous basis.
Harmonic
Distortion
A distortion at the output of a device where the amplified input signal is accompanied by the sum
of unwanted signals that are harmonics o the input signal. Harmonic distortion can be expressed
as a percentage of the total output intensity, or in decibels. See also Distortion.
Headphones /
Headsets
Headsets are headphones with microphones added. Headphones and headsets are available in a
wide range of variations. Some of the variations include: Lightweight, Heavyweight, Medium
Weight: Lightweight can often be used or worn for a ten hour shift with only mild discomfort;
medium weight usage ranges from two to six hours continuous, and heavy weight usage ranges
from 15 minutes to 2 hours. Acoustic Isolation: which varies from 0 dB to 40 dB. Usually more
isolation means a heavier headset. Acoustic Isolation (30 to 40 dB) is required in high ambient
noise environments such as concerts, auto racing, construction areas, aircraft engine run-up, near
machinery such as printing presses. Medium isolation (10 to 20 dB) is required in quieter
concerts, near crowds, near quieter machinery. Low acoustic isolation can be tolerated in