Handbook for Sound Engineers

Transmission Techniques: Wire and Cable 409

• Some feature overall shields to reduce crosstalk and
  facilitate star grounding.


• Allows easier and cheaper installs than using
  multiple single channel cables.

Snakes come with various terminations and can be
specified to meet the consumer’s needs. Common termi-
nations are male or female XLR (microphone) connec-
tors and ¼ inch male stereo connectors on one end, and
either a junction box with male or female XLR connec-
tors and ¼ inch stereo connectors or pigtails with
female XLR connectors and ¼ inch connectors on the
other end.
For stage applications, multipair individually
shielded snake cables feature lightweight and small
diameter construction, making them ideal for use as
portable audio snakes. Individually shielded and jack-
eted pairs are easier to install with less wiring errors. In
areas that subscribe to the NEC guidelines, the need for
conduit in studios is eliminated when CM-rated snake
cable is used through walls between rooms. Vertically
between floors, snakes rated CMR (riser) do not need
conduit. In plenum areas (raised floors, drop ceilings)
CMP, plenum rated snake cables can be used without
conduit. Color codes for snakes are given in Table 14-12.

14.9.3 High Frequency Pairs

Twisted pairs were original conceived to carry low-fre-
quency signals, such as telephone audio. Beginning in
the 1970s research and development was producing
cables such as twinax that had reasonable performance
to the megahertz. IBM Type 1 was the breakthrough

product that proved that twisted-pairs could indeed carry

data. This led directly to the Category premise/data

cable of today.

There are now myriad forms of high-frequency,

high-data rate cable including DVI, USB, HDMI, IEEE

1394 FireWire, and others. All of these are commonly

used to transport audio and video signals, Table 14-13.

14.9.3.1 DVI

DVI (Digital Visual Interface) is used extensively in the

computer-monitor interface market for flat panel LCD

monitors.

The DVI connection between local monitors and

computers includes a serial digital interface and a

parallel interface format, somewhat like combining the

broadcast serial digital and parallel digital interfaces.

Transmission of the TMDS (transition minimized

differential signaling) format combines four differential,

high-speed serial connections transmitted in a parallel

bundle. DVI specifications that are extended to the dual

mode operation allow for greater data rates for higher

display resolutions. This requires seven parallel, differ-

ential, high-speed pairs. Quality cabling and connec-

tions become extremely important. The nominal DVI

cable length limit is 4.5 m (15 ft). Electrical perfor-

mance requirements are signal rise time of 0.330 ns, and

a cable impedance of 100: FEXT is less than 5%, and

signal rise time degradation is a maximum of 160 ps

(picoseconds). Cable for DVI is application specific

since the actual bit rate per channel is 1.65 Gbps.

Table 14-12. Color Codes for Snake Cables

Pair

No.

Color

Combination

Pair

No.

Color

Combination

Pair

No.

Color

Combination

Pair

No.

Color

Combination

Pair

No.

Color

Combination

1 Brown 13 Lt. Gray/Brown stripe 25 Lt. Blue/Brown stripe 37 Lime/Brown stripe 49 Aqua/Brown stripe

2 Red 14 Lt. Gray/Red stripe 26 Lt. Blue/Red stripe 38 Lime/Red stripe 50 Aqua/Red stripe

3 Orange 15 Lt. Gray/Orange stripe 27 Lt. Blue/Orange stripe 39 Lime/Orange stripe 51 Aqua/Orange stripe

4 Yellow 16 Lt. Gray/Yellow stripe 28 Lt. Blue/Yellow stripe 40 Lime/Yellow stripe 52 Aqua/Yellow stripe

5 Green 17 Lt. Gray/Green stripe 29 Lt. Blue/Green stripe 41 Lime/Green stripe 53 Aqua/Green stripe

6 Blue 18 Lt. Gray/Blue stripe 30 Lt. Blue/Blue stripe 42 Lime/Blue stripe 54 Aqua/Blue stripe

7 Violet 19 Lt. Gray/Violet stripe 31 Lt. Blue/Violet stripe 43 Lime/Violet stripe 55 Aqua/Violet stripe

8 Gray 20 Lt. Gray/Gray stripe 32 Lt. Blue/Gray stripe 44 Lime/Gray stripe 56 Aqua/Gray stripe

9 White 21 Lt. Gray/White stripe 33 Lt. Blue/White stripe 45 Lime/White stripe 57 Aqua/White stripe

10 Black 22 Lt. Gray/Black stripe 34 Lt. Blue/Black stripe 46 Lime/Black stripe 58 Aqua/Black stripe

11 Tan 23 Lt. Gray/Tan stripe 35 Lt. Blue/Tan stripe 47 Lime/Tan stripe 59 Aqua/Tan stripe

12 Pink 24 Lt. Gray/Pink stripe 36 Lt. Blue/Pink stripe 48 Lime/Pink stripe 60 Aqua/Pink stripe

Courtesy Belden.