Yamaha MG82CX Bedienungshandbuch PDF herunterladen (Seite 7)

Mixer Basics

MG82CX/MG102C Owner’s Manual

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

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.

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 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 decibel

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.

Noise cancelled

Balanced noise cancellation

Noise

Hot (+)

Ground

Cold (–)

Cable

Source

Receiving device

Phase

inversion

Noise-free

signal

Phase

inversion

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.

+ 20 dBu

0 dBu

0.775 V

20 dBu

40 dBu

60 dBu

The inputs and outputs on

home-use audio gear

usually have a nominal level

of –10 dBu.

Most professional mixers,

power amplifiers, and other

types of equipment have

inputs and outputs with a

nominal level of +4 dBu.

Microphone signal levels

vary over a wide range

depending on the type of

microphone and the source.

Average speech is about

–30 dBu, but the twittering

of a bird might be lower than

–50 dBu while a solid bass

drum beat might produce a

level as high as 0 dBu.

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