In or out?

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In or out?
Over on the PS Audio YouTube channel, there's a spirited debate over terminology. In a balanced signal, are the two halves out of polarity or out of phase? I suppose the fact viewers are in a heated discussion over such semantic differences is a good thing. Or maybe it means folks have more time on their hands than I imagine. The answer is both are accurate though one is more technically correct than the other. Phase generally refers to a change in time while polarity is absolute. In balanced audio, we have two conductors with signals, each 180˚ out of phase with the other. As one signal is rising its mate is falling. Sum the two signals together and they should perfectly cancel each other out and we get zero signal. We use this difference between the two to our advantage. If our balanced signal is fed into a balanced input, then only the difference between the two signals is amplified (and they are 180˚ different from each other). Any signal common to both signals is rejected (called common-mode rejection). Hum and other noises leaking into the balanced cable are eliminated. So here's the rub. If we say the two signals are of opposite polarity to each other we communicate correctly what the signals are that make up a balanced cable. It is also accurate to say the two signals of opposite polarity are out of phase with each other. So, both are correct though one way of expressing it makes for fewer arguments among us nerds. The trick about communicating is to make sure you're speaking clearly to the audience and that they understand. Or, find an audience with less free time on their hands to argue about such trivia.
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Paul McGowan

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