Balanced and unbalanced lines

What are audio lines?

Hello, this time we will talk about an important topic in audio. It is related to how to interconnect equipment, this is: balanced and unbalanced lines. When we talk about a line (transmission line) we mean the cable used to carry the electrical signal. The cable type we use can make an important difference in the transmission quality. This is due to the electrical characteristics of the conductor's material and the signal's frequency.

So we must know the application to use the best audio cable for the job. Different cables are needed for: microphones, guitars, speakers, digital signals, etc.

Unbalanced lines

Unbalanced lines are the simplest and thus, the most common found in lower-cost or semi-professional equipment. It consist of two wires: positive (+) and ground (GND). The most common connector for this kind of line is the TS (tip, sleeve) plug or "mono" plug.

TS plug

In these connectors the tip is positive. Then we find a plastic strip and then the ground, which is the sleeve. The cable only needs two poles for unbalanced signals. Another type of unbalanced connector is the RCA. This is used for video and audio signals. While the audio quality is not degraded with good quality RCA connectors, it is recommended to use TS whenever possible.

RCA

The main disadvantage of an unbalanced line is that the signal is more vulnerable to interference and noise. This could come from motors, lights or radio signals. An unbalanced cable is only useful for distances less than 5 meters (15 ft.). For longer distances the risk of noise increases. Anyway, these lines are still very common. They are the standard connections for electric guitars, keyboards and devices such as tablets, mobile phones or MP3 players. This is because the typical distances for these devices are not large.

Balanced lines

These lines use cables with three poles: positive (+), negative (-) and ground (GND). The signal travels in both the positive and the negative wires, but it does so with reversed polarity in the negative one. For proper operation it requires special audio inputs in the equipment. These inputs need a circuit called differential amplifier that can receive both signals, positive and negative. This feature of receiving two equal signals with reversed polarity allows so much more immunity to noise and interference. On the other hand, its implementation a bit more complex and expensive. The connectors used for balanced signals are the TRS plug (stereo) and the XLR (Cannon).

TRS and TS plugs

In the case of TRS, the tip (3) carries the positive signal. The ring (2) carries the negative signal and the sleeve (GND) closes the circuit. The TRS connector has two insulating strips (4), while the TS has only one. It is important to notice that, as in the TRS two signals can travel at the same time, it is often used to carry an unbalanced stereo signal. This means that the right and left signals are sent on the same cable. An example of this application is the headphone cable. In the case of the mini-plug (3.5 mm) the connections are the same as the standard plug. The mini-plug connector could be both TS or TRS versions.

The XLR (Cannon) also has the same functionality as the TRS, but it is more robust and secure. In this case each pin is numbered and has a standardized function: Pin 1 ground (GND), pin 2 positive (+) and pin 3 negative (-). The numbers are indicated on the connector itself.

Cannon

As we said, balanced lines are much more effective against noise. A balanced line can easily reach 50 meters (150 ft.) without noise problems. This is why they are the best way to connect pro audio gear. Finally, we must clarify that it is not possible to balance a signal just by changing the type of connector or cable. For example, to put a TS at one end of the cable and an XLR at the other. This merely serves to adapt connectors but the signal remains unbalanced at the end of the XLR.

The correct way to balance a signal is using a "direct box" (DI Box). These boxes have internal balancing circuits (usually transformers) that do the balancing job. Using DI Boxes can lead to an important investment, but it is worth it if good audio quality is what we are looking for. We can find active (amplified) and passive (without amplifier) DI Boxes.

DI Box