Audio Engineering

Balanced and Unbalanced Transmission Systems (3)

The Music Telegraph | Text 2019/04/05 [12:48]
Audio Engineering

Balanced and Unbalanced Transmission Systems (3)

The Music Telegraph| 입력 : 2019/04/05 [12:48]

▲ When audio enters a balanced cable, both the (+) and (-) wires receive identical versions of the signal. The only difference is, polarity of the (-) wire is inverted. As the two signals travel along the cable, both wires gather noise, the same way unbalanced cables do. However, before re-combining them at the opposite end of the cable, the polarity of the negative wire is flipped back, to once again match the positive signal. With the noise patterns now on opposite polarities, they cancel each other out, leaving the original signal noise-free.

© E-Home Recording Studio



 

Balanced and Unbalanced Transmission Systems (3)

 

 

When to Use Balanced vs. Unbalanced Lines

We come to the point where we should decide on an arbitrary set of rules guided by the state of technology in the field of audio, regarding the time and place for the use of balanced and unbalanced lines. (Let us just add before any final deductions are made that in both cases the amount of interference picked up by the line is proportional to the length of it. However, this factor will be neglected at present.) The set of rules we have to establish are to be developed based on the experimentation and experience of many audio specialists and engineers in this field. 

 

 

 

Microphone Lines

Let us start with microphone lines: Don't ever attempt to use unbalanced mic input lines unless they are shorter than a few inches. This includes the mic for the talkback system within a console, announcer mics on goosenecks with the mic wires going directly into the preamp input, or any microphone with a built in amplifier (e.g., FET condenser microphones which may have output levels far exceeding levels of conventional microphones). Although it is possible to run some mic lines unbalanced, no self respecting professional would dare to run these lines any other way than balanced.

 

 

 

Line Level Signal Processors

In the cases where interconnection of several pieces of equipment with unknown ground potentials and different power supplies is expected, balanced lines are mandatory. This refers to patch bays in particular. You never know what equipment you will be called upon to patch in and the only sure way to prevent ground loops, noises, and melted patch bays, amplifiers, and power supplies is to use balanced lines isolated with transformers.

 

The goal of today's processor designs is to process the signal from the source to the final destination with the least amount of deterioration of quality. In this age of miniaturization, and high performance standards, the transformer is frequently the most objectionable part of the system, so a tendency exists to eliminate it from as many circuits as possible and replace them with active op amp circuitry. This is a healthy one, but we will never get to the point where transformers can be entirely eliminated. Take for example, the recording and live sound console.

 

 

 

Consoles

The only place experience dictates should use transformers for isolation and balanced lines is on all inputs and outputs from the console. All the rest of the circuits within the console can be unbalanced and there is no other reason than having access to parts of the circuitry balanced, to do otherwise.  

 

 

 

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