Making The Most Of Your Mixer; Balanced, Unbalanced-What's The Difference; Signal Levels And The Decibel - Yamaha MG166C Owner's Manual

Mixer Basics

Making the Most of Your Mixer

You've got yourself a mixer and now you're ready to use it.
Just plug everything in, twiddle the controls, and away you go ... right?
Well, if you've done this before you won't have any problems, but if this is the first time you've
ever used a mixer you might want to read through this little tutorial and pick up a few basics
that will help you get better performance and make better mixes.
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 sur-
rounded 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 con-
fined 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 micro-
phones 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.
Balanced noise cancellation
Hot (+)
Cold (–)
Phase
inversion
Ground
Source

Signal Levels and the Decibel

Let's take a look at one of the most commonly used units in
audio: the decibel (dB). If the smallest sound that can be
heard by the human ear is given an arbitrary value of 1, then
the loudest sound that can be heard is approximately
1,000,000 (one million) times louder. That's too many digits
to deal with for practical calculations, and so the more appro-
priate "decibel" (dB) unit was created for sound-related mea-
surements. In this system the difference between the softest
and loudest sounds that can be heard is 120 dB. This is a
non-linear scale, and a difference of 3 dB actually results in a
doubling or halving of the loudness.
You might encounter a number of different varieties of the
dB: dBu, dBV, dBM and others, but the dBu is the basic deci-
bel unit. In the case of dBu, "0 dBu" is specified as a signal
level of 0.775 volts. For example, if a microphone's output
level is -40 dBu (0.00775 V), then to raise that level to 0 dBu
(0.775 V) in the mixer's preamp stage requires that the signal
be amplified by 100 times.
A mixer may be required to handle signals at a wide range of
levels, and it is necessary match input and output levels as closely as possible. In most cases the "nominal" level
for a mixer's input and outputs is marked on the panel or listed in the owner's manual.
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MG206C/MG166CX/MG166C Owner's Manual
Noise
Phase
inversion
Noise cancelled
Receiving device
Cable
To summarize
Microphones
Short line-
level runs
Noise-free
Long line-
signal
level runs
Most professional mixers,
power amplifiers, and other
+ 20 dBu
types of equipment have inputs
and outputs with a nominal level
of +4 dBu.
0 dBu 0.775 V
The inputs and outputs on
home-use audio gear usually
have a nominal level of –7.8 dBu
(–10 dBV).
-20 dBu
Microphone signal levels vary
over a wide range depending on
-40 dBu
the type of microphone and the
source. Average speech is
about –30 dBu, but the twitter-
-60 dBu
ing of a bird might be lower than
–50 dBu while a solid bass
drum beat might produce a level
as high as 0 dBu.
Use balanced lines.
Unbalanced lines are fine if
you're in a relatively noise-
free environment.
The ambient electromag-
netic noise level will be the
ultimate deciding factor, but
balanced is best.