Talk:What does balanced mean?/@comment-31022905-20171228232910

To start at the beginning: 'Balanced' refers to a plus and a minus version of the signal (inverted copy as aptly mentioned above), that are each others opposite in voltage (=amplitude). These two versions run over two conductors, with ground (the third conductor) usually running around the former two, in order to shield them from RF interference. The interference may be led away to earth, in the case of true ground, but in any case does not connect to the signal path anywhere.

Single ended on the other hand, has only one conductor carrying the signal, thus delivering only half the amplitude of the two-conductor setup, while noise that's gathered during the transmission basically remains the same in amplitude. Balanced, in other words, offers you practically twice the SNR that single ended does, simply because it doubles the amplitude of the signal but not of the noise.

We might add that well designed amplifiers tend to have a high CMRR spec. The Common Mode Rejection Ratio refers to the extent to which the amp rejects current that both conductors have 'in common' while accepting current that is different (like the opposite copies in two balanced 'differential' conductors).

This spec is of little use when applying single ended connections: even when your conductors are twisted, usually evening out the amount of interference picked up by each conductor (making the interference 'common' to both wires!), one of the conductors is 'signal ground', meaning the amp is not receiving a signal input from that conductor anyway. So by using SE instead of balanced, we throw away a valuable instrument for fighting RF noise, included in every amp that has balanced input connectors.

Mostly other words for the same story as above, hope it helps some.