There are two ways to send audio signals from point A to point B via copper cables: symmetrically and asymmetrically also referred to “balanced” and “unbalanced”. There are many beliefs surrounding audio signals, some claiming differences can even be heard using in-ear headphones! To shed light on these myths, we addressed this issue in a much simpler way.
The symmetrical (or balanced) cable was invented to solve a fundamental problem in sound transmission: noise/ interference from outside the cable. Eliminating external interference at the root cause would be physically impossible, so therefore the solution lay in the exclusion of it: by duplicating the signal on a separate wire before it is transmitted through the cable. More importantly, one of the two signals is inverted. This is a process called balancing and is illustrated in the following diagram:
Because of the inverted phase signal, these two signals cannot be mixed at the other end of the cable, as they would simply cancel each other out. At this point, the phase of one of the two is recovered and mixed with the original. But then where does the magic happen? The background noise/interference is captured by both signals and the phase-inverted signal will cancel the one on the regular phase, and voila … The noise is canceled! In mathematics, it would be displayed as so: x + (-x) = 0
As you can see, balanced connections are the perfect option in minimizing noise/interference, especially in longer distances accompanied by the presence of electronic devices along the way. Unfortunately, the classic “hum” of 50Hz cannot be removed, as this has something to do with the ground connection. But that’s a whole nother story …
In order for the balanced signal to be transmitted correctly, both the source and the target device must be equipped with this option. Signals produced by microphones, for example are almost always balanced, as they have a moderately low output level and are thus vulnerable to external noises before entering the preamp. Instrument signals, however, are almost always unbalanced. Fortunately, modern audio interfaces can process signals depending on the type of Line / Instrument controls. Line inputs are often designed as XLR while accepting balanced connections, but also allow you to connect TRS / Jack cables and therefore unbalanced signals. It’s not possible to have a balanced signal in the presence of simple “TS” links which is missing the extra contact that transmits the inverted signal mentioned earlier. Situations like this are rare and are usually found using low-cost audio interfaces, when manufacturers save on the cost of the components needed for the circuitry.
Don’t worry if you accidentally happen to “mix” balanced cables and instruments to equipment that only work with unbalanced connections, there is no risk of damaging anything. The worst thing that can happen is that you won’t be able to hear anything.
Incidentally, there is balanced and also unbalanced signals for the digital world, where noise/interference can be even more invasive as it does not allow the interface used to properly “read” the signal. The coaxial formats S / PDIF and AES / EBU formats do not differ much in size as in the physical differences of transmission: the first uses unbalanced connectors ( “RCA”), while the AES / EBU comes with the classic 3-pin balanced XLR cables.
The balanced transmission is the preferred choice for obtaining the signal routing as free from problems as possible. In the world of microphones it’s the only possible transmission, whereas in other areas it is increasingly preferred as long as it is possible to have compatible equipment (XLR or TRS). With very long cables (we’re talking tens of meters, for example), using balanced cables is practically a must. In addition, balanced cables are able to supply the power required by microphones or active DI Boxes (phantom power). Basically, everything that revolves around the world of miking requires balanced cables.
Guitar and bass players would normally rarely use balanced cables. A guitar, bass guitar, pedal or amplifier have always operated on an unbalanced signal. When distances are a problem, then a buffer is preferred. Only when miking an amplifier /cabinet or when the guitar signal is sent via line-out on the mixer are balanced cables necessary.
Keyboard players normally use unbalanced cables, as their connections are usually quite . short and simpleIn addition, many keyboards only have TS connection. For longer distances it is best to use a DI Box, which in this case requires a balanced output cable that goes to the mixer.