Live Audio: The Art of Mixing a Show by Swallow Dave

Author:Swallow, Dave...
Language: eng
Format: epub
Published: 2014-04-24T08:02:29.487000+00:00

CHAPTER 10

Line Systems

After you’ve put up your desk and outboard racks, you’ll have to run out your multicore (or at least get one of the very helpful local crew to run it out for you). Multicores are also known as snakes, or sometime just referred to as the multi; they are the method of getting mic lines from the stage to each console, and then getting the audio back to the on-stage power amps and monitor console. (We’ll go into more detail about multicores later in this chapter.)

In professional systems, the signal paths work as follows:

Input Source: Vocals, guitars, keyboards, etc.

Microphone or DI box: we’ll go into these in the next chapter when we talk about setting up the stage.

Stage box

Splitter rack

Multicore

Consoles

Returns

To properly understand how and why these systems work, and why we use them, we need to first look at unbalanced and balanced lines.

UNBALANCED LINES

Unbalanced line cables are frequently used for connecting guitars and keyboards into a PA system. Inside, they have a single insulated core, around which is wrapped a screen, which is a mesh of wire. This screen acts as a shield against electrostatic hum fields and RFI (radio frequency interference).

These kinds of cables normally have a mono quarter inch jack socket on them. You can identify the difference between a mono and a stereo jack by the amount of rings it has on it; a mono jack has a single tip that separates the single core from the screen, and a stereo jack has a tip and a ring. A mono jack system is great for connecting things over short distances. However, for cable runs over about 18 feet, the cable starts to act like a massive aerial and will pick up more noise than you want in your circuit. This, of course, is a big problem if you’re trying to send audio to the front of house console and then back again—they are usually more than 18 feet away.

To solve this problem, you must use a balanced line.

BALANCED LINES

The majority of professional equipment, including microphones, mixing consoles, and outboard, use the balanced line system. But what does it do, and why do we use it? And, most importantly, how does this affect our mix?

To explain this concept, we need to first look at what balancing is. The basic idea behind a balanced line is that, unlike its unbalanced counterpart, it rejects any hum fields that can be picked up by the cable. To understand why, think about the cable that carries the signal. The cable consists of a pair of wires twisted together, known as a dual core. The pair have two different colors; one is referred to as hot, and the other as cold. They are wrapped together so that they are both subject to the same interference (electrostatic noise picked up by the cable). They are then wrapped in a screen, which is a mesh of wire that surrounds both internal cables and shields the cable carrying the audio from external electrostatic fields.

Each

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