Pairing

This is particularly important on balanced systems. On unbalanced systems, all signals are referenced to the same point, usually earth. For example, RS-232 uses pin 7 on a DB25 as the reference point and the transmit line goes to plus and minus 15 volt w.r.t. pin 7 etc. On a balanced system, the transmit would be with respect to itself etc., and both these require two wires each. Any noise induced in one wire will be induced in the other and so cancel each other out at the receiver, assuming the two wires are very adjacent to each other. What we do is twist them together and this is called pairing. It's vital that we get correct pairing to have effective noise immunity.