Balanced Signals – XLR

Posted: September 29, 2015 by TGASMrDunne in Classwork, hardware, Techniques
Tags: , , , , , ,

The XLR cable is a fantastic system for preserving signal quality over long distances, but the way it works is difficult to understand. Hopefully this mini guide will help!

We start off with the cable itself.

Kabel-Symetrisch.png

There are three conductors, one acts as the shield (and ground) and the other two carry the main signal, however one pin carries the unaltered signal (hot) and one carries the inverted polarity signal (cold).

balanced-waveform

If noise or interference penetrates the shield and gets through to our hot and cold conductors, it will be added to the voltage of each conductor equally.

Polarity noise added

When we reach the input end of the signal chain (mixer, amp etc) the cold signal is inverted again, leaving us with the following.

Polarity noise input flip

Notice how the original signal is identical, but the noise is now in opposite polarity! When we combine these signals, we are left with…

signal final

A noise free signal, stronger than the original! (Any noise included with the original signal will of course still be present at the input stage.)

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