D8 Skills #70 | How XLR Cables Cancel Noise
Two days ago, we learned how XLR cables cancel out noise introduced in their path by a demonstration in Pro Tools. It was really interesting, and today I successfully did it myself in Logic.
It uses a technique called CMRR which stands for Common Mode Rejection Ratio. It works by having two duplicates of audio travelling through the cable, however, one of them is inverted meaning they're cancelling each other. When noise is introduced somewhere along the cable, it'll be the same (not inverted) in both signals. This means that when the two signals reach the mixing desk, the inverted signal can be flipped back to normal so that any noise that was introduced along the path of the cable gets cancelled out, and we're left with a clean signal.
You can see in the two channels above that the sine waves are the same as each other, however, the wiggles on the waves are opposite to each other. It's easiest to notice this at the two tiny rectangular waves right after the play head.