14 EMX512SC/EMX312SC/EMX212S
Making the Most of Your Mixer
BASIC
type connectors will also handle
unbalanced signals with no
problem. Microphone cables
usually have this type of
connector, as do the inputs and
outputs of most professional
audio gear.
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 levels 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.
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
effectively canceled while the
audio signal is left intact. Clever,
eh?
Hot
Cold
Shield
(Ground)
Outer
Insulation
Balanced Unbalanced
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.
Balanced noise cancellation
Noise
Hot (+)
Cold (–)
Ground
Source Cable
Noise cancelled
Noise-free signal
Phase
inversion
Receiving device