TM

UNDERSTANDING BALANCED

AND UNBALANCED AUDIO

TECHNOLOGY

MARKET: Security, Professional

Video, Videoconferencing

DOC. NUMBER: T-09

When designing a distribution system for audio,

one of the first determinations that an installer must

make is whether the system needs to support bal-

anced or unbalanced audio. While, in theory, all au-

dio signals may be transmitted in either a balanced

or unbalanced format, in practice, different indus-

tries have opted to use one or the other type of sig-

nal because of the costs and benefits involved. In

general, consumer-level electronics use an unbal-

anced signal, while professional-level equipment

uses balanced audio. As a result, any fiber optic

transmission system connecting such equipment

must be designed or configured to support the ap-

propriate type of signal.

Within the

Fiberlink

line of transmission

systems

there are several products designed

to support

line level audio in both unbalanced and

balanced formats (1 volt rms with 600 Ohms im-

pedance). This TECHnique reviews the basic dif-

ferences between unbalanced and balanced audio,

so that the installer has a better understanding of

each underlying technology.

In short, unbalanced audio is less expensive to support than balanced audio. Among other things, it

requires less expensive connectors and fewer wires. Not surprisingly, the trade-off is a lower sound qual-

ity and limited cable distance. By comparison, balanced audio generates a cleaner signal with less hum

and noise. Due to economics, different industries have adopted either balanced or unbalanced audio as

the standard used by audio equipment designed for use within their respective marketplaces. In general,

consumer-level electronics, such as simple microphones and VCRs for the home, use unbalanced audio.

While the signal from these devices is not as clean as it could be using balanced audio, most consumers

would be unwilling to pay the price for these electronics if balanced audio technology were incorporated

into their designs. Similarly, industrial applications tend to use unbalanced audio signals, as in these envi-

ronments, the requirements for sound quality are quite low. Basic functionality is usually sufficient. Con-

versely, professional level equipment, such audio mixers, amplifiers and broadcast equipment use bal-

anced audio. In these applications, the users of the equipment are far more concerned with ultimate sound

quality than with budgetary restrictions.

The accompanying diagram shows the details of both types of interfaces. In an unbalanced system, the

input is referenced to ground. The system is designed to interface with common, single-conductor, shielded

Fiberlink

is a trademark of Communications Specialties, Inc.

© 1999, Communications Specialties, Inc.



Page 2:

UNDERSTANDING BALANCED AND UNBALANCED

AUDIO TECHNOLOGY

cable and two conductor connectors, such as RCA

phono plugs or standard ¼ inch phone plugs. The

reason this design provides lower quality than a bal-

anced is system is because signals caused by un-

equal ground potentials (called “ground loops”) can

be conducted through the cable’s shield and inter-

fere with the audio.

In a balanced system, the input is often transformer

coupled (although electronic non-transformer

equivalent circuitry does exist). This type of system

uses twisted pair cable, which can be shielded or

unshielded. The audio signal travels through two con-

ductors at the same time, but 180 degrees out of

phase. Meanwhile, any interfering signals travel

through both conductors in the same phase. The

result is that interfering signals, such as hum, are

cancelled out, while the original audio signal is con-

ducted in its pure form. Typically, balanced audio

configurations use multi-pin connectors, such as

common XLR-style connectors, or even simple ter-

minal blocks. A center tap in the transformer wind-

ing may also be used to provide additional shielding

purposes.

•

Pure Digital Fiberlink

system for

4 Channels

Audio ....................

4040 Series

•

Pure Digital Fiberlink system for

16 Channels Audio

.......................

4160 Series

•

Pure Digital Fiberlink system for

32 Channels

Audio .....................4320

Series

•

Educational Guide:

An Introduction to

Fiber Optics

•

Educational Guide:

Advantages

of Digital

Transmission Over Fiber

Note that a balanced input can often be converted

into an unbalanced one by simply grounding one

side of the transformer or equivalent input.

In those cases where the ultimate in low noise high

quality audio transmission is desired, not only should

the balanced configuration be used, but shielded

twisted-pair cable with proper grounding should also

be employed.

© 1999, Communications Specialties, Inc.