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Balanced, Unbalanced- What's the Dierence?
In a word: "noise." The whole point of balanced lines is noise rejection, and its some-
thing 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 conned to your desktop and
all connections are no more than a meter or two in length, then unbalanced lines are
ne-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 amplied to an alarming
degree in the mixer's high-gain head amplier.
Balanced Noise Cancellation
Microphones
Short Line - Level runs
Long Line - Level runs
Use balanced lines.
Unbalanced lines are ne if you’re in a relatively
noise free environment
The ambient electromagnetic noise level will
be the ultimate deciding factor, but balanced is best
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 appropriate "decibel" (dB) unit was created for sound-related measurements.
In this system the dierence between the softest and loudest sounds that can be
heard is 120 dB. This is a non-linear scale, and a dierence of 3 dB actually results in a
doubling or halving of the loudness.
You might encounter a number of dierent varieties of the dB: dBu, dBV,dBM and
others, but the dBu is the basic decibel unit. In the case of dBu, "0 dBu" is specied 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 amplied 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 panelor listed in the owner's manual.
Most professional mixers, power ampliers, and other
types of equipment have inputs and outputs with a
nominal level of +4 dBu
The Inputs and outputs on home-use audio gear usually
have a nominal level of -7.8 dBu (-10 dBV).
Microphone signal levels vary over a wide range
depending on the type of microphone and the source.
Avarage speech is about -30 dBu, but the twittering of a
bird might be lower than -50dBu while a solid bass
drum beat might produce a level as high as 0 dBu
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