Balanced and unbalanced audio and AC power

After much skull scratching and soul searching, I decided to combine several concepts into one section, because they are so intimately interconnected. No, not that intimately, they ’ re just good friends. So in this section I ’ ll talk about unbalanced and balanced audio, unbalanced and balanced AC power, and the best ways to wire and clean up the sound (and picture) of your studio/disco/home theater/whatever.

Unbalanced/balanced audio
Let ’s start with audio; a nice, simple bit of audio – a sine wave. Some of you may have seen a sine wave on an oscilloscope or in a picture. They all look more or less like the one in Figure 2.3.1 .

Since the sine wave is AC (alternating current), it will start at 0 V (zero volts), rise to a positive peak, then reverse itself, cross the 0 V reference line again, and rise (inversely) to its negative peak. Or it will do what I’ve shown here: start negative and fl ip positive. And it will keep doing this, over and over, until we get bored and turn it off.

If the sine wave repeated this action 1000 times in a second, we ’ d say it has a frequency of 1000 Hz (hertz) or, in older terminology, 1000 cps (cycles per second). We audio folks got tired of saying ‘ see-pee-ess ’ and renamed the unit of measurement ‘hertz’ as it ’s shorter.
Higher frequency sine waves will appear more squished together horizontally;
lower frequency sines will look more spread out. The reason for this is that the horizontal axis in an oscilloscope is the ‘ time base ’ – it shows the progression of the waveform from the past into the future. The more times a signal reverses polarity, the higher its frequency and the more reversals present in a given period of time.

All sound (almost) is made up of complex combinations of AC (alternating current) waveforms, most of which are not sine waves. The only exception is a DC (direct current) pulse, which will make a one-time ‘ click ’ when connected to a speaker or headphone, but not much else.

We use sine waves for measurement because they ’ re easy to quantify.
I hope you are now fine with sine, as it were, and ready to see how this applies to real-world situations.There are only two ways that an analog audio signal can be carried along in a wired connection. For the sake of brevity (and sanity – mine), I ’ m not going to expound on digital or RF transmission of audio.
The simplest way for an audio signal to be carried on a wire is as an unbalanced signal. This means that there is a center conductor (hot), and (typically) shield and ground are combined in the outer layer of the wire. So half of the signal path is (sort of) shielded by the outer layer, and the outer layer itself is tragically vulnerable to interference from sources in the outside world.
What this means is that unbalanced audio is basically limited to runs of 20 feet or less, and even then it lacks the ability to null out induced noise, hum and the other crud we encounter with great ah, frequency.

Balanced audio, on the other hand, can survive runs of hundreds of feet, so all pro audio facilities use balanced mic lines, balanced transmission lines, and do most of their internal wiring in a balanced manner. We ’ ll explore what unbalanced/balanced wiring is after we take a quickpeek at a couple of guitar plugs to show you the physical difference between balanced/unbalanced connectors.