Cables

      Balanced vs. Unbalanced?

Audio cables (analog) can be either balanced or unbalanced, depending on their intended use. For long cable runs, especially when using relatively low microphone levels, a three-wire balanced audio circuit reduces noise. Balanced audio cables use the principle of phase cancelation to eliminate noise flow while maintaining the original audio signal.

A balanced audio cable sends the same audio signal on two wires, but inverts the phase of one signal by 180 degrees.

When noise is introduced into the cable, it is introduced equally to both the original and the inverted signal.

When the signal arrives at its destination, the inverted signal is put back in phase and both signals are combined. This puts the original and inverted signals back in phase, but it causes the noise signals on each line to be out of phase.

Now, both audio signals are in phase, but the noise is inverted, causing the noise to be canceled. At the same time, the original signal gets a little stronger because it is sent on two wires and combined. This helps compensate for the reduction in signal strength that occurs naturally on a long cable run.

Any noise introduced into the cable across its long run is almost completely eliminated by this process.

Note: Unbalanced cables have no way of eliminating noise and are therefore not as robust for long-distance cable runs, microphone signals, and other professional uses.

Analog signal cables.

Paired Wires

Wires which are in a configuration keeping them somewhat closely spaced together are paired wires. Paired wires can resist some noise due to cancellation of the signals created on the wires by the electromagnetic noise going in the same direction.

Twisted Pairs         

Twisted pairs are wires which are closely spaced as well as twisted around each other. Twisting the wires together makes it easier to keep the wires close together, and in addition greatly increases the noise rejection due to the twisting itself creating more or less equal exposure to the noise signal dependent on the twist ratio and frequency of the noise generated field.

Twisted Pair with Shield (Balanced Cables)

The shielded twisted pair is a twisted pair with a shield (braid or foil, etc) surrounding the twisted pair. Basically used in balanced audio, you have a twisted pair with a common ground which is electrically between the two. Opposite polarity signals are applied between each wire and the shield. Using a transformer or electrical circuitry the signals are combined back together re inverting their polarities so they are additive, and the noise on them is subtractive. Balanced lines like this therefore have even greater noise immunity than twisted pairs and are excellent at running signals very long distances with very low noise. 

Coax Cable

The area where Coaxial cables spank twisted pairs, and therefore are so worthwhile for so many applications is in maintaining a constant impedance which becomes very important at higher frequencies.