Multi-Track Recording

Unbalanced Signals

An unbalanced cable consists of two connectors with two conductors each, connected by two wires inside the cable—a signal wire and a ground wire.  You can quickly (in most cases) identify a cable designed to carry an unbalanced signal by its connectors: because each wire has to terminate at the connector with its own contact point, an unbalanced cable requires only two conductors at the connector. A standard TS (or “tip-sleeve”) guitar cable is the unbalanced cable you’ll run into on stage most. Standard RCA cables used for many AV components are also unbalanced cables.

Inside the cable itself, the signal wire is typically in the center of the cable with the ground wire surrounding it. The ground wire serves two functions—it carries part of the audio signal and serves to shield the main signal wire to some degree from outside interference from noise such as the hum from lights and transformers, as well as RF (radio frequency) interference that comes from TV and radio transmissions. It does a decent job of rejecting noise, but unfortunately, the wire itself also acts like an antenna and picks up noise.

Unbalanced cables work great for connecting a guitar to an amp, for instance, but because they are not very good at suppressing noise from outside interference, unbalanced cables should have a maximum length of 15-20 feet (4-6 meters), especially when used in noisy environments and with signals that are low level to begin with, such as those from keyboards, guitars, MP3 devices and so on.

Balanced signals

A balanced cable, by contrast, has three conductors in the connector and three wires in the cable: two signals wires plus a separate ground wire. As in the unbalanced cable, the ground wire still surrounds the signal wires and is used as a shield against interference. But what makes a balanced cable special is the way the gear utilizes that extra signal wire.

So why would you want audio gear that flips the polarity of your signal? In this case, because the receiving gear will flip the inverted signal back into its original orientation. But because both copies of the signal picked up the same noise as they traveled along the cable—and that noise is identical on the two wires in the cable—flipping the polarity of what arrives at the receiving gear will produce the original signal intact and noise which now has reversed polarity. Summing that gives you a welcome result: signal that’s preserved and noise that’s canceled.

Because of this, balanced cables can support much longer cable runs; 50 to 100 feet (15-30 meters) is not uncommon, though even shorter runs will often use balanced wiring to protect against noise. The wiring for microphones, and the interconnect cables between consoles, signal processors, and amps, etc.,  in a pro sound system or recording studio environment are typically of the balanced variety. Standard connectors designed for use with balanced signals are XLR and TRS (or “tip-ring-sleeve”).

Direct boxes are called "DI" boxes, which stands for "Direct Injection".

Their primary purpose is to convert unbalanced or high-impedance instrument signals into a signal suitable for direct connection to the microphone input of a mixing console - whether live on stage or in the recording studio. As it says above in the section about balanced and unbalanced signal the advantage of using a DI box is that you can run longer cables and not get unwanted noise.

Here are some audio interfaces. They are used to convert the analogue signals from instruments and microphone to digital signals that go in to the computer.