Unbalanced audio refers to a type of audio signal transmission where the signal is carried over a single conductor (usually a wire) along with a ground or reference conductor.
Umbalanced lines are more susceptible to electromagnetic interference as long as ground can pick up interferences.
It could be used for runs under 5-6 meters to minimize noise issues. (the larger the conductor surface, the greater the probability of interference).
Balanced systems
Balanced audio refers to a type of audio signal transmission where the signal is carried over two conductors along with a ground or reference conductor.
In a balanced connection both wires transmit the same audio signal but the audio signal is sent 180 degrees out of phase between the two wires.
Those wires are called "Hot wire" and "Cold wire". The hot wire carries the original audio signal and the cold wire carries the phase-reversed audio signal (180 degrees).
Balanced lines cancel out any noise that has been introduced along the cable (see Operating Principles below).
This technique is commonly used in professional audio equipment to ensure high-fidelity sound over long cable runs and in noisy environments.
Operating principles
In balanced systems, the audio signal is cloned. The Hot Wire carries the original audio signal voltage and the Cold Wire carries the same audio signal voltage but 180 degrees out of phase.
In math terms, all the voltages values from the hot wire audio signal are multiplied by -1 and then are sent over the cold wire at the same time.
Thus, in a pedagogical way it could be said there is a "positive" audio signal and a "negative" audio signal: Signal and -Signal.
When electromagnetic interference reaches a conductor it causes voltage spikes that generates noise in the audio signal.
In a pedagogical way it can be said that voltage spikes are a wave that result in a Wave Superposition with the audio signal wave.
This wave superposition between the electromagnetic interference and the audio signal is an addition.
In the figure above, is represented the interaction between the Hot wire audio signal and the electromagnetic interference.
However, as long as Hot wire and Cold wire are placed pyshically together inside the cable, when the electromagnetic interference reaches the cable, it affects the both wires in the same way.
This means, the same electromagnetic interference wave is interacting with both wires and been added to both audio signal waves in the same way.
It is important to note, this only happens because both wires are pyshically together. If each wire were far from the other, then the electromagnetic interference could not be the same on each wire.
Following with the previous figure, below is the representation of the Cold wire audio signal interaction with the electromagnetic interference.
At this point, there are two waves: (Signal + Noise) and (-Signal + Noise).
Next, when waves reach the end of the cable, the hardware performs a substraction between the Hot wire wave and the Cold wire wave.
In math terms this is: (Signal + Noise) - (-Signal + Noise)
Clearing the parameters, results in: Signal + Noise + Signal - Noise
Clearing again: Signal + Signal
Finally: 2 * Signal
The balanced input of the hardware always perform the wave substraction between Hot wire and Cold wire. Resulting in the noise removed and the audio signal amplitude doubled.
That process is called diferential inputs. This allows noise rejection, better sound quality and longer cable runs.
