Sound Track: The Balancing Act

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.

1. 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.
   

   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.

2. But why is balanced audio better than unbalanced?

   For one simple reason: balanced signals actually cancel noise the cable picks up.
   

   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).

3. 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.

4. 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 eliminate.
   

   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.

5. My camcorder has a 1/8-inch mike input. How can I tell if itís balanced?

   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).

6. 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 input jack.
   

   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.

7. 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 noise.

8. 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.

9. 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.

10. 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.