Music is a massive bunch of these squiggles all thrown in together, but it can be represented for our purposes as a single squiggle line. Now picture this squiggle line, and let’s mentally cut it in half horizontally. The upper half is just the tips of the wave, and the lower half is just the troughs. Because of the time element and the way the wave is shaped, the tips never line up vertically with the troughs.
Balanced cables, also known as XLR cables by the typical connectors used at the ends, take advantage of this fact to pull off something special: “common mode noise rejection.”
Picture sound-canceling headphones for a moment. They use microphones to listen to surrounding noise, and they inject that noise into your music, delayed half a wave. So they change a tip into a trough, and the tips and troughs of the surrounding noise align vertically.
When this happens, sound cancels out. That’s why they’re called noise-cancelling headphones instead of noise-reducing headphones — they really do nix that business right out.
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