7
There are two methods of connecng analogue audio devices, using either “Balanced” or “Unbalanced”
connecons. By far the most common is unbalanced – the main reason for this is cost - fully balanced system uses
almost twice as many components as a typical unbalanced system.
Unbalanced inputs
A normal, unbalanced system uses interconnects with just two conductors (normally using RCA connectors)—an
inner core that carries the audio signal, and an outer sheath that acts as a “Ground” or 0V reference. In an ideal
situaon, this would be all that is needed. Unfortunately, as well as transferring the intended signal, a cable is also
very eecve at picking up radio frequency noise. This noise can be generated by many things, for example the
operaon of light switches, thermostats , or uorescent lamps will commonly produce RF ‘spikes’. The result is a
combinaon of the two signals, as illustrated below:
Unfortunately, once the signal has become corrupted with noise, there is no method of removing this noise
without further damaging the original signal.
Balanced inputs
A balanced input uses a clever technique where instead of having just one signal conductor, there are two (as well
as a Ground). The standard connecon for a balanced input is the 3-pin XLR connector.
This method sends the original signal along one of the conductors, and a second idencal, but inverted one, down
the second conductor. Now, if this signal is corrupted by the same noise signal, both signals will be aected
idencally. Note the orange plot, which shows the inverted signal, the signal remains inverted, but the noise is not;
this is because, being in close proximity to each other, the two conductors pick up the noise signal at exactly the
same me (and therefore phase).
Now when the two wave forms are recombined (by subtracng one from the other, the noise cancels
itself out, leaving the original, noise-free signal.
Balanced and unbalanced inputs
Original signal Signal + noise
Balanced Signal Balanced signal + noise Recombined signal
