Balanced Wiring
Where protection from electromagnetic interference and freedom from earth references are required, a balanced interface is used. The term ‘balanced’ refers to identical (balanced) impedances to ground from each of two signal carrying conductors which are enclosed within an all-embracing overall electrostatic screen. This screen is grounded (to catch and remove unwanted RFI), but plays no part in passing the audio signal or providing its voltage reference. Instead, the two signal wires provide the reference for each other — the signal is conveyed ‘differentially’ and the receiver detects the voltage difference between the two signal wires. Any interference instils the same voltage on each wire (called a common mode signal) because the impedance to ground is identical for each wire. As there is therefore no voltage difference between the two signal wires, any interference is therefore ignored (rejected) completely by the receiver.