Balanced Cables

Garret C. Maynard
July 2004

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Audio cables can be the weakest link in the chain of sound recording. When deploying external microphones, videographers need to know the difference between unbalanced and balanced cables.

The best way to understand the difference between balanced and unbalanced cables to think in terms of signal separation. You can remember how it works by thinking of a balanced cable with three wires, one for the positive, one for the negative and one for the ground: X=ground, L=left or positive and R=right or negative. XLR, get it? Unbalanced cables have two wires, one for the positive and one that acts as both the negative and the ground. Such a configuration means that the negative wire is doing more "work" than the other: therefore, we could call it "unbalanced."

Balanced cables are better because they have a separate wire for the ground, which means they are less susceptible to extraneous noise. Their XLR connectors often have a locking mechanism that makes the connections more reliable and more difficult to accidentally unplug. Unbalanced phone, mini and RCA connectors are not hearty and can be easily damaged and dislodged from their inputs. Balanced cables often also include a tight metal mesh wrapper that acts as an electronic shield to protect them from interference. Electricity can generate hum through a broken cable or a damaged connector. It can even arise simply by laying a power cable parallel to an audio cable. The upshot to all this is that hum in a cable can ruin an audio recording.

Balanced and unbalanced audio adapters potentially need to do two things. First, an adapter might physically change the connections to match each other, say from an XLR plug to a 1/4-inch phone jack. Second, an adapter might electronically change the impedance of a signal so that it matches the source to the destination. Impedance is a characteristic that refers to the resistance a sound signal encounters as it goes through a system. Some adapters only do one of these things and some do both. Or you might need to combine two different adapters in a chain to connect your equipment fully.

Professional microphones are balanced, use XLR connection and are of low impedance. Consumer equipment is unbalanced, does not use XLR connections and often has high impedance. Be careful when using adapters because some lack the electronic component necessary to properly match the signal levels used in XLR cables and those used in mini-inputs. This can definitely create buzz in your audio and could potentially damage your equipment. Fortunately, you can purchase adapters and boxes that can compensate for the impedance differences. Beachtek, Canon, Sign Video and Studio 1 (among others) manufacture the boxes that take care of both the physical connection and any impedance difference.

Many professional camcorders have XLR connections ready for microphones. Sometimes there are inputs for two channels, left and right for stereo recording, but a single XLR input is always mono. If a consumer camcorder has a microphone jack, it is almost certainly a stereo mini plug (1/4-inch).

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