A balanced signal is the cleanest way to get audio from point A to
point B. Any questions?
Weíve all heard of a balanced diet, a balanced composition and
a balanced checkbook. But what the heck is balanced audio? Thatís
a good question, one weíll answer along with nine more good questions
about balanced audio.
- What is balanced audio?
Balanced audio is nothing more than a special way to carry an audio signal
down a cable (the other common way being called unbalanced). The reason
for this special method of signal-carrying is to eliminate electronic noise–any
unwanted electromagnetic radiation that creeps into the cable, causing an
audible hiss and a reduction in the overall quality of your sound.Advertisement
In a normal unbalanced cable, one piece of wire–or "conductor"–carries
the moving electrons that make up the audio signal. Around this conductor
is a shield that intercepts electromagnetic noise and carries it harmlessly
away from the signal.
A balanced cable uses two signal-carrying conductors encased in a shield,
instead of just one. One of these conductors carries the normal audio signal,
while the other carries an inverted (or "out of phase") version
of the same signal. When the signal on one conductor swings in a positive
direction, the signal on the other swings negative by the same amount. When
itís received on the other end by a balanced connector, a circuit
flips the inverted signal over and adds the two together.
- But why is balanced audio better than unbalanced?
For one simple reason: balanced signals actually cancel noise the cable
Hereís how: when unwanted noise gets past the shield of an unbalanced
cable, it hitches a ride on the inner conductor and becomes a permanent
part of the signal. Thereís nothing you can do to get rid of it.
When noise breaks through the shield of a balanced cable, it affects both
inner conductors equally. In other words, the energy from the noise goes
in the same direction on both conductors. When the input stage of the receiving
device flips the inverted half of the balanced signal back over, the two
signals combine in-phase to create a stronger result. The noise on one conductor
is now out-of-phase with the noise on the other, effectively canceling itself
out of existence when the input stage combines them (see Figure 1).
- How can I tell if something uses balanced audio?
A distinct tip-off is when you see a wiring system that makes three electrical
connections (remember that balanced audio requires two conductors plus a
shield). The most common balanced audio jack is the XLR connector–itís
circular, about 3/4-inch across and has three small pins or sockets. Professional
mikes almost always have male XLR connectors on their ends; professional
recorders and decks usually have female XLR inputs.
Though not as common, you may find gear that uses a 1/4-inch tip-ring-sleeve
connector to carry balanced audio. Itís more likely that a 1/4-inch
"phone" jack will be carrying unbalanced audio, as evidenced by
its two-conductor (tip-sleeve) connector.
- How do I know if I need balanced audio?
The most obvious sign that you need to move towards balanced audio is
the presence of unwanted noise in your audio. While some noise is a result
of bad cables or improper grounding, much of it comes through the air. Weíre
surrounded by electromagnetic radiation in our everyday lives; it comes
from radio transmitters, power lines, electric appliances–even the sun
itself. Itís these types of noise that balanced cabling will help
Your need for balanced audio is proportional to the length of your signal
run, and inversely proportional to the strength of your signal. In other
words, if you have extremely long cable runs or very weak signals, you need
balanced audio. If you have both (a long mike cable, for example; compounding
length and a weak signal), then a balanced line is a must.
- My camcorder has a 1/8-inch mike input. How can I tell if itís
Odds are, itís not; you almost never find balanced audio flowing
through a 1/8-inch or "mini" jack. If your camcorder records in
mono, the 1/8-inch minijack mike input is expecting a tip-sleeve connector
carrying the output of one unbalanced mike. If your camcorder is a stereo
model, the input is probably set up to accept two unbalanced mikes on a
single tip-ring-sleeve plug. This is where things get a little confusing.
Three conductors on a minijack usually point to a stereo unbalanced connection,
not balanced mono.
The world would be a much friendlier place for audio folk if manufacturers
would either standardize audio connections or label them clearly. Unfortunately,
you rarely find either. The only way to be sure what type of audio is in
use is to try it. Power amps aside, you canít really hurt audio equipment
by plugging things in wrong (thank goodness).
- I want to use balanced audio, but none of my video equipment supports
it. What do I do?
The easiest and most effective place to start using balanced audio is
in an external microphone. Professional mikes with balanced connectors are
affordable and easy to come by, as are balanced mike cables. Since your
camcorder wonít accept a balanced signal, use an inexpensive transformer
to convert the balanced signal to an unbalanced signal right at your camcorder.
You can find balanced line (or "impedance-matching") transformers
at Radio Shack and other electronics stores. Shure Brothers (222 Hartrey
Ave., Evanston, IL 60202; (847) 866-2200) makes the A97F ($51), a quality
transformer thatís used by many prosumer videographers. It converts
a balanced mike signal into an unbalanced minijack output, and even includes
a short cable to ease mechanical strain on your camcorderís mike
Balanced audio is of the greatest benefit when protecting very weak audio
signals. The mikeís output signal is as weak as they come, making
it the ultimate candidate for balanced signals. Even if you use balanced
signals at the microphone and nowhere else, they can make a huge difference
in the health and well-being of your audio.
- Do I need to run balanced audio between my mixer and my record deck?
If your mixer has balanced outputs and your deck has balanced inputs,
by all means use them. If one (or both) of these components doesnít
support balanced audio, youíd have to rig up transformers and converters
to run balanced audio. This isnít worth the hassle for two reasons:
first, signals flowing between audio components like mixers, audio recorders
and VCRs are quite strong. This makes them much less susceptible to stray
electrical noise. Second, one rarely has to run cables more than a few feet
to connect audio components, further reducing the risk of picking up unwanted
- I have an unbalanced accessory mike that sits on top of my camcorder.
Should I use transformers to balance and unbalance the signal?
Probably not. Even though the signal flowing from mike to camcorder is
small and vulnerable, the cable run is extremely short. This makes it unlikely
your audio will pick up much noise in its short trek to your camcorder.
Should you use a longer cable to move the mike 10 or 20 feet from your camcorder,
however, you may need to use a balanced line.
- Iíve never seen any consumer gear with balanced audio. Why?
First, manufacturers donít perceive the need to grace consumer-level
equipment with professional-level connectors. The assumption on the part
of manufacturers is that there are too few videographers needing these features
to justify putting them on the equipment. In essence, theyíre right.
If youíre using balanced audio or professional mikes with your camcorder,
youíre in the minority.
Second, balanced connectors and the added electronics they require cost
money. Putting these on a camcorder may drive the retail price up, making
that model less cost-competitive in the market. Finally, balanced connectors
(XLR being the most common) are quite large. Few compact consumer camcorders
have the real estate to spare for these connectors.
- All my local electronics store has is RCA-style audio cables and
unbalanced mikes. Help!
To find these products, you may need to turn to a local music store.
The balanced mikes and cables youíre looking for find more use in
live music than video, and are easy to locate at stores that sell PA (public
address) equipment and instruments.
Many mail-order video equipment companies sell balanced mikes and cables
to cater to professional video production companies. You can probably find
what you need right here in the pages of Videomaker.