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How do balanced Audio systems work? It's actually very simple yet very smart and effective move to eliminate cable noise. First of all the signal path is not comprised of one ,,hot'' wire and one ground wire. The signal is actually split in two wires, one carrying the original signal and the other carrying a phase inverted copy of the signal. Since opposing vectors cancel each other, the amplifier on the far end of the cable must invert one of the signals so that they would be in phase and their amplitudes will be summed and not substracted. In RF terms this is called constructive interference, as opposed to destructive interference caused by out of sync signals mixing. Noise picked up by the cable is in the same phase for both conductors, so when the amp inverts one of the phases, the noise actually becomes cancelled on the amp side, leaving only the audio signal. There is usually a third conductor added to the whole cable, which is usually grounded and acts as a shield to further minimise noise. Ingenious little trick for long cables and sensitive audio equipment.
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