Balanced cables what?

The real catch

Simply speaking, a balanced cable helps to reduce noise from your audio interface to your speaker (or any other audio connection between two audio terminals).

Additionally, considering that the signal is duplicated while traveling, a balanced cable can serve a better distance between two audio-connected terminals.

So how does it work?

A balanced audio cable will carry two different signals. One with the original phase and one with the phase rotated of 180 degrees (producing a mirrored copy of the signal). At the end of the cable, one of the two signals will have its phase reversed again and be mixed with the original signal.

Any noise introduced during the transmission, by reversing the phase of the signal, will be theoretically eliminated. Let's see how this works with some examples:

First we will play a simple sine oscillator with the original phase:

And now let's play a copy of the sound with the reversed-phase (the oscillator phase is rotated of 180 degrees):

They sound similar, right? The traveling signal is the same! Now let's try to mix the two sound sources and have some fun. The slider at the bottom of the oscilloscope will allow us to change the phase of the mirrored signal. The starting phase of the second traveling signal is 0°, try to play the signal with a phase rotation of 180°.

What happens when the mirrored signal is rotated at 180°? Did the volume go down to zero? The signals are still traveling in the same direction, but, as the phase of the mirrored signal is reversed, the output is equal to zero, the signal is effectively muted. How does this help with noise?

Let's imagine that while the signal is traveling, some noise is introduced in the path. The noise would have the same phase in the main signal and the mirrored one. At the end of the travel, the mirrored signal would be rotated again to the original phase together with the introduced noise which then would be reversed in phase. The resulting signal would have eliminated the noise as its phase would be reversed. Makes sense?

Q&A Time

- What's the difference between a balanced cable and a balanced stereo cable?

In theory, as the phase reversion happens in the supplier of the signal and the receiver, a stereo cable could work as a balanced cable, however, in practice, that's not the case.

The difference between a stereo cable and a balanced cable is that the stereo cable is composed of two sheaths, each one with a shield so that the single stereo channel can travel with some interference protection. A balanced cable is composed of a single sheath, 2 conductor cables, and a shield. In a balanced cable, the wires are twisted together so to improve the CMMR (Common Mode Rejection Ratio) of the wires that transport the signal.

- Does the inversion of phase happen in the cable itself?

No, the inversion of phase happens in the supplier and receiver of the signal. Thus, the cable is not responsible for the inversion of the phase. The supplier of the signal and the receiver will have to take care of switching the phase of the signal to 180 degrees.

References:

• Thread on Quora