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Audio for Video Production: Balanced Vs. Unbalanced

In the battle for Audio City, Balanced Man stands alone as the only hero left to fight the evil Unbalanced Signal... Well, that's how this article was going to start, until I really started thinking about it. You see, in the real world, balanced audio signals are the reliable, professional way to go, while unbalanced connections are prone to problems. That didn't make for much of a villain. At the same time, there are many legitimate uses for unbalanced audio. That left me with more of a superhero and a sidekick that could work together, but with no substantial enemy. It's a work in progress. In the meantime, I think we'll just discuss the differences between balanced and unbalanced audio connections and how to use them both in your productions.

The concept of a balanced audio signal can be difficult to grasp since you can't see sound - either in the air or as it's converted to electricity and traveling down your cables. But we can get a better look once it's inside the computer. Open an audio file in your favorite sound editing application. The first thing you'll notice is a center zero line with information above and below the line. Zoom in a little closer and you'll see that the audio waveform is evenly distributed in the upper and lower regions. This is a balanced audio signal. Using the zero line as a reference point, the audio contains equal amounts of positive and negative information. This is seen in the movement of the woofers in your home or car stereo. With no signal, the woofer cone sits in a neutral - or zero position. When an audio is played through the speaker, the woofer travels forward and backward in response to the positive and negative portions of the audio signal.

A balanced audio connection works the same way. If you look closely at the end of an XLR connector, you'll see the pins numbered 1, 2 and 3. Pin #1 is the zero voltage or ground connector. Pin #2 carries the positive portion of the audio signal while Pin #3 carries the negative portion. Many years ago, telephone engineers discovered that this was a great way to send audio signals very long distances with a minimum of loss. Later, the broadcast world found that balanced audio connections helped eliminate interference from transmitters and other signals. Finally, the professional audio world signed on and today, you'll find balanced audio connectors on everything from microphones to mixers and most of the devices in between.

Using our previous example, imagine a zero line with all the audio information above it. It looks a little odd, but that's how unbalanced audio works. An unbalanced audio connection has two electrical connections: a positive or signal wire and a zero or ground wire. You can also see this type of signal at work if you can find an old speaker and a 9-volt battery. Simply touch the battery across the terminals of the speaker and then release it. You will see the speaker cone move in one direction rather than two because it's receiving an unbalanced signal - zero and positive voltage only. With nothing to balance things out, unbalanced audio connections don't travel well over long distances and often pick up interference from nearby transmitters and electronic devices.

However, there are plenty of perfectly good uses for unbalanced audio signals. Most electronic musical instruments - guitars, basses and keyboards - use unbalanced audio outputs. Since the signal only needs to travel a few feet, this is a simple, effective solution. Many budget wireless microphones use unbalanced audio outputs too. This keeps costs down and, since you're probably plugging the receiver directly into a mixer or camcorder, there is little chance for interference. The microphone and line input connections on your computer soundcard are unbalanced too. Because of this, you will sometimes hear faint noises in the background when you move your mouse or type on the keyboard. Computers generate a lot of internal noise and the unbalanced connection can't keep it all out of the audio. You can also hear the effects of noise pickup if you place your cell phone near some computer speakers. 25 feet is the maximum length of cable for an unbalanced signal, and you'll do well to keep it as short as possible.