MG8/2FX
8
Making the Most Of Your Mixer
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 con-
ductors 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?
1-3. Signal Levels—Decibel Do’s and Don’ts
From the moment you start dealing with things audio, you’ll have to deal with the term “decibel” and its abbreviation, “dB”.
Things can get confusing because decibels are a very versatile unit of measure used to describe acoustic sound pressure levels as
well as electronic signal levels. To make matters worse there are a number of variations: dBu, dBV, dBm. Fortunately, you don’t
need to be an expert to make things work. Here are a few basics you should keep in mind:
●
“Consumer” gear (such as home audio equipment) usually has line inputs and outputs with a nominal (average) level of
–10 dB.
●
Professional audio gear usually has line inputs and outputs with a nominal level of +4 dB.
●
You should always feed –10 dB inputs with a –10 dB signal. If you feed a +4 dB signal into a –10 dB input you are likely to
overload the input.
●
You should always feed +4 dB inputs with a +4 dB signal. A –10 dB signal is too small for a +4 dB input, and will result in
less-than-optimum performance.
●
Many professional and semi-professional devices have level switches on the inputs and/or outputs that let you select –10 or
+4 dB. Be sure to set these switches to match the level of the connected equipment.
●
Inputs that feature a “Gain” control—such as the mono-channel inputs on your Yamaha mixer—will accept a very wide range
of input levels because the control can be used to match the input’s sensitivity to the signal. More on this later.
Normal-phase signal
+ normal-phase noise.
Normal-phase signal
+ reverse-phase noise.
Desired signal
with no noise.
