Making the Most Of Your Mixer

MG10/2

8

1-2. Balanced, Unbalanced—What’s the Difference?

In a word: “noise.” The whole point of balanced lines is noise rejection, and it’s something they’re very
good at. Any length of wire will act as an antenna to pick up the random electromagnetic radiation we’re
constantly surrounded by: radio and TV signals as well as spurious electromagnetic noise generated by
power lines, motors, electric appliances, computer monitors, and a variety of other sources. The longer
the wire, the more noise it is likely to pick up. That’s why balanced lines are the best choice for long
cable runs. If your “studio” is basically confined to your desktop and all connections are no more than a
meter or two in length, then unbalanced lines are fine—unless you’re surrounded by extremely high lev-
els of electromagnetic noise. Another place balanced lines are almost always used is in microphone
cables. The reason for this is that the output signal from most microphones is very small, so even a tiny
amount of noise will be relatively large, and will be amplified to an alarming degree in the mixer’s high-
gain head amplifier.

To summarize:

Microphones: Use balanced lines.
Short line-level runs: Unbalanced lines are fine if you’re in a relatively noise-free environment.
Long line-level runs: The ambient electromagnetic noise level will be the ultimate deciding factor, but
balanced is best.

■

How Do Balanced Lines Reject Noise?

** Skip this section if technical details make you queasy. **

Balanced lines work on the principle of “phase cancellation”: if you add two identical signals out of
phase (i.e. one signal is inverted so its peaks coincide with the troughs in the other signal), the result is …
nothing. A flat line. The signals cancel each other out.

A balanced cable has three conductors:

1) A ground conductor which carries no signal, just the “ground” or “0” reference against which the
signal in the other conductors fluctuates.
2) A “hot” or “+” conductor which carries the normal-phase audio signal.
3) A “cold” or “–” conductor which carries the reverse-phase audio signal.
While the desired audio signals in the hot and cold conductors are out of phase, any noise induced in
the line will be exactly the same in both conductors, and thus in phase. The trick is that the phase of
one signal is reversed at the receiving end of the line so that the desired audio signals become in-
phase, and the induced noise suddenly finds itself out of phase. The out-of-phase noise signal is effec-
tively canceled while the audio signal is left intact. Clever, eh?
Normal-phase signal.
Reverse-phase signal.
No signal.
(Phase cancellation)
Normal-phase signal
+ normal-phase noise.
Normal-phase signal
+ reverse-phase noise.
Desired signal
with no noise.

MG10_E.book Page 8 Monday, May 26, 2003 1:52 PM