Balanced Audio Explained
Posted: 13 July 2010
Synopsis: Balanced audio, put simply, is a means to transfer an audio signal through a cable without picking up any electrical hum, often referred to as noise or noise-floor.
Balanced audio, put simply, is a means to transfer an audio signal through a cable without picking up any electrical hum, often referred to as noise or noise-floor.
Electrical hum is everywhere. It is the electrical energy in the air itself. It is most noticeable when there's a lot of electrical equipment around. Stage lights are particularly bad when it comes to electrical hum.
When electrical energy is transferred, it will always give off excess energy into the air, which is in turn picked up by other electrical circuits, particularly cables, as they are essentially a very long distance circuit.
The shielding on cables does to help negate the pickup of renegade electricity, but does not stop it completely, so fancy audio technicians came up with balanced audio.
An unbalanced cable (regular guitar cable) has two wires. One of them transmits your audio signal, known as the "conductor". While the other is a "ground" wire (earth), ensuring that any excess signal has somewhere to go and doesn't make unwanted noise clogging up your amp circuitry.
A balanced cable (XLR microphone cable or TRS cable) consists of three wires. This time there are two "conductor" wires and one "ground" wire.
When a balanced signal starts its life in your microphone or mixing desk or wherever it might have been born, it consists of two identical signals being sent in parallel. The jack on your mic or mixer then inverts one of these signals before sending it down the two separate conductors of your XLR or TRS cable.
But what does that mean, inverting a signal? Well, think of a signal as a waved line like so:
Notice there are troughs and peaks, which repeat in a cycle. This is very similar to how electrical energy works in a circuit.
If the above is the original signal, our inverted signal would look like this:
The inverted signal is doing the opposite thing from the original, but at the exact same time.
If you were to combine both the inverted and original signals, they would cancel each other out perfectly as they are exact opposites, leaving no signal at all.
|Now, remember how we spoke about renegade electrical energy being picked up? Well, in our balanced cable, the same electrical hum is being picked up by both conductors (original and inverted). Think of the angry red line as our unwanted electrical noise.|
Now here's the special part. When the balanced signal reaches its destination balanced jack at the other end of the cable, the inverted signal becomes reverted to the same as the original.
Remember how we spoke about opposite signals cancelling each other out. Now the electrical noise of the reverted signal is now an inverse of the electrical noise of the original, and when the two signals are combined, the electrical noise cancels itself out; thus we have no electrical hum, like so:
It is important to use balanced cables with microphones (low impedance especially) as they output such a low strength (voltage) signal which makes the signal very susceptible to electrical hum. This is even more important when using long microphone cable lengths. Balanced cables are also a good idea when there are many cables running near each other, especially power cables.
Line Level signal outputs and inputs can often be balanced on professional audio equipment such as mixing desks. It is less important to use balanced cables for line level signals, having a higher strength signal means they are less susceptible to electrical hum. Though again, for longer lengths and when around there are many other cables around, using a balanced XLR or TRS cable is a good idea.