Balancing Act

Understanding balanced and unbalanced audio connections can help you record better audio. As a youngster, I loved to go to the circus. The sights and sounds of the big-top fascinated me especially the tightrope walkers. These were people who risked life and limb, balanced high above the crowd with only a thin wire between them and certain peril. That fascination stayed with me over the years and, when I started dealing with audio equipment, I realized there was a lesson to apply from my childhood.

In this article, we’ll look at the difference between balanced and unbalanced audio connections, where they are used and how they benefit you as a video producer.

Walking the Wire

Consider the intrepid tightrope walker. He climbs up to the wire and starts to walk across arms extended for balance. Then, a gust of wind comes along and blows directly in his face, but because of his outstretched arms, the wind affects him evenly. His journey is a bit more difficult, but the wind does not throw him off balance. Now imagine that we tie one arm behind his back for the next trip across the wire. Once again the wind gusts, except now he has only one arm for balance. You guessed it, he falls this time because the wind pushed on his one arm, throwing him off balance (don’t worry, he’s OK – it was a practice wire and just a few feet off the ground).

But let’s apply this analogy to your audio connections. A balanced audio signal, like our tightrope walker, travels down the wire with an equal amount of signal on either side of an imaginary line. There are three wires in a balanced audio connection (Figure 1B): ground, hot (or positive) and cold (or negative). The ground wire functions as the tightrope, with the positive and negative portions of the audio signal serving as the outstretched arms. In this configuration, an audio signal can travel for hundreds of feet, virtually unaffected by interference or signal loss. Why? Because any interference that might harm the signal is equally applied. At the receiving end of the cable (your mixer or camcorder), the audio circuit understands the correlation of the positive and negative portions of the signal to the ground wire. Since each part of the signal is distinct, any extraneous noise or interference is considered an outsider and is cancelled.

Interfering Signals

Interference takes many forms, but falls into two main categories: RFI (radio frequency interference) and EMI (electro-magnetic interference). RFI comes from anything that generates radio waves radio and TV stations, cell phones, intercoms, etc. Of course, all these items have legitimate uses, but when the radio energy intrudes on your audio signal, it becomes interference. EMI comes from things that generate a magnetic field by electrical means; camcorder/laptop power supplies and computer monitors are notorious for this. You can minimize the effects of interference by keeping your audio cables and connections away from these noise generators.

Unbalanced cables use only a ground wire and one other to transfer their signals (Figure 1A). As a result, all the audio activity takes place on one side of the tightrope, so to speak (Figure 2A). This allows interference to corrupt the signal easily due to the inability to cancel the noise at the receiving end of the cable. Of course, unbalanced connections still have their applications. A microphone signal can usually survive up to 25 feet of cable length before the risk of interference is too great. Unbalanced line-level signals work at lengths of 50 feet or more in many applications. Your results will vary based on how much potential interference exists at your recording location. A remote shoot at the base of a radio station tower is a bad idea.

Connectors

You’ll encounter a wide variety of audio connectors in the video world (see photo). Professional microphones use balanced three-pin connectors, generally referred to as "XLR." Some microphones and mixers use a 1/4-inch connector for audio connections (also called a "phone plug" from their origin in telephone switchboards). These connectors come in two and three conductor flavors for unbalanced and balanced applications. The little brother of the 1/4-inch connector is the 1/8-inch or mini-plug connector. This type of plug is often the only way to get external audio into your camcorder. Modern digital cameras use a three-conductor version for stereo audio, but don’t confuse three conductors with a balanced connection. This application provides two unbalanced inputs in one connector. Finally, there is the RCA connector or phono plug – a classic unbalanced connector used for simple audio and video hookups.


Application is Everything

Balanced audio connections offer low noise, high signal quality and operate over long distances. They are always superior to the unbalanced alternative. So why doesn’t everything use them? The answer is simple. Unbalanced audio connections work fine for short distances under low-interference conditions, and they’re cheap to manufacture. On the other hand, balanced connections require better wire, pricey connectors, more circuitry inside the equipment and more connector real estate on the outside. All of which translates into more cost for the consumer. Further, balanced audio connections are considered a professional option. That’s why you only find balanced audio options on cameras costing upwards of $2,000.

Does that mean you can’t use balanced audio with your $500 camcorder? Of course not. Here’s what you need to benefit from balanced audio. First, your camcorder must have microphone input; most are the 1/8-inch variety. Next, you need a balanced audio source. Many hand-held microphones, some wireless mikes and all audio mixers will qualify. Finally, you need the cables and connectors to go from the balanced output to the input of your camera. How do you know for sure you have a balanced audio source? If the connector is XLR, it’s 99.9 percent certain. If the connection is 1/4-inch, you should consult the equipment manual. If the connection is 1/8-inch or RCA, you’re out of luck.

Adapting the balanced cabling to the unbalanced input of your camcorder requires a trip to your local electronic parts store. First on the list is a balanced XLR plug to an unbalanced 1/4-inch plug adapter. Next, you need to convert the male 1/4-inch plug to a 1/4-inch female jack. Then, convert the 1/4-inch female into two RCA female jacks. Last on the list is a longish cable that has two RCA male plugs on one end and a 1/8-inch stereo plug on the other perfect for plugging into your camcorder. Why all the adapters? There isn’t a simple, inexpensive way to convert balanced, professional connections into unbalanced ones. This setup has two major benefits. The adapter configuration is designed to accept two balanced signals for stereo; just add another balanced-to-unbalanced adapter. The other benefit of this setup is that the camcorder end is a simple cable, not a weighty combination of adapters and connectors, which could potentially break off in your camera. You can lay the heavy stuff on the floor or tape it to your tripod.

But is there really a benefit to running balanced audio for 50 feet, only to convert it to unbalanced for the final 6 feet? Yes, here’s why. Even at shorter distances, the balanced arrangement naturally rejects noise and interference, resulting in cleaner audio. Unless you live in the shadow of a clear-channel AM radio station, the short, unbalanced portion of the cabling will be insignificant.

Visit the Big Top

For your next production, remember the lesson of the tightrope walker and try some of the balanced audio alternatives we’ve discussed. You’ll gain some creative options and the quality of your sound will shine like it never shined before. Now, where’s that hot-dog vendor?

Sidebar: Shielding

Whether balanced or unbalanced, all audio and video cables are shielded to help eliminate interference. Cable shielding takes several forms: spiral-wrap, braided and foil. Spiral-wrap is the simplest type. A layer of bare copper strands wraps around the center wire(s) and provides 60 to 75 percent surface coverage. Braided shielding takes a basket-weave approach to protect the signal wires and typically provides 90 percent coverage. Foil shielding is simply aluminum foil attached to a plastic backing and offers 100 percent coverage to the signal wires. Although foil seems like the best method, percentage-wise, these cables are normally less flexible than their copper cousins. In addition, copper shielding provides more resistance to EMI than aluminum foil.

Sidebar: What’s My Level?

Audio signals come in a variety of levels or volumes. The two you’ll deal with on a regular basis are microphone-level and line-level. Microphone-level is just what is says, the level of electrical signal that comes from a typical microphone. This is a very small signal and is easily swamped by external interference. Line-level is much higher in volume and, as such, is less prone to corruption. Typical line-level devices are CD players, VCR and camcorder audio outputs. Just don’t get the two confused. A microphone plugged into a line-level input won’t register any sound. A line-level device plugged into a mike input will sound fuzzy and distorted.

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