Handbook for Sound Engineers

Intercoms 1573

tion, impedance matching, and level sets between
systems. Additionally, it supports external relay activa-
tion and call sense circuitry. Typical circuits include
4-wire telephone lines, camera intercoms, two-way
radios and microwave links, four-wire intercoms, fiber
optic lines, and satellite links. Other types of four-wire
circuits include IFB systems, ISO systems, and program
audio in/out.
Many matrix systems have the capability of linking
to other matrix systems. This allows stations in one
system to communicate with stations in other systems
and anything that can be selected or controlled in one
system can be selected and controlled from any other
linked system. This allows independent systems in
remote locations, even in different cities, to operate a
single system.
The station-to-matrix wiring in matrix systems can
operate in either a three-pair mode or a four-pair mode.
Using the four-pair scheme, remote station operation is
possible from any location that can provide a standard
four-wire audio circuit plus a four-wire RS-422 data
circuit back to the central matrix. This can include

transmission links such as satellite and fiber optic

circuits, T-1 channel banks, ISDN, and switched 56

terminal adapters.

Port input signals are usually routed through soft-

ware controllable digital potentiometers. This enables

remote control of input levels from a PC, or directly

from the intercom control stations, allowing instant on

the fly adjustment of audio signals that are too loud or

too soft.

Because the audio is digital, noise pickup is nonexis-

tent, frequency response is 100 Hz–15 kHz ±1 dB,

distortion is less than 0.5% ,and the SNR is greater than

60 dB.

43.2.4 Program Interrupt (IFB)

IFB is a television production trade acronym that stands

for interrupted feed-back, interrupted fold-back, inter-

rupted return-feed, and in some cases prompt-mute. IFB

plays an important role in the behind-the-scenes activi-

ties that make a production, as it permits the director or

Figure 43-13. 8 × 24 program two-wire party line matrix with presets. Courtesy Clear-Com Communication Systems.

MS-812A 8

RCS-2700

RM-702 GM-18

STAGE RIGHT

DIRECTOR

19 03

03

POWER SUPPLY

POWER SUPPLY (REDUNDANT)

RCU-67 (OPTIONAL)

COMPUTER

EF-1M

FIBER MODEM

TO BLACK

FIBER MODEMTO REHEARSAL HALL

RS-501

CC-95

CAMERA-1 CAMERA-2

RS-501

CC-95

IMAG

RM-702 GM-18

TELEPROMPTER

RM-702 GM-18

LIGHTING

RM-704 GM-18 FOH AUDIO-1

FOH AUDIO-2

RM-704 GM-18

ORCHESTRA

RM-702 GM-18

STAGE RIGHT

STAGE RIGHT

STAGE LEFT

STAGE LEFT

STAGE LEFT

TWO WAY

RADIO

CUSTOM CABLE

9-PINMALE TW-47

CUSTOM CABLE

EF-1M TW-47 9-PINMALE TWO WAY

EXISTING FUTURE EXPANSION

8 X 24 PROGRAM MATRIX WITH PRESETS

CC-260

WBS-680 WIRELESS INTERCOM