Yamaha EM5014C - Manual (Page 13)

Making the Most of Your Mixer
EMX5014C Owner’s Manual 13
Mixer Basics
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.
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?
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.
Hot (+)
Cold (–)
Ground
Balanced noise cancellation
Unbalanced noise
Noise
Source Cable Receiving device
Source Cable
Phase
inversion
Noise
Noise-free
signal
Phase
inversion
Receiving device
Receiving device
Noise cancelled