Appendix A: General Information - Mackie SR24•4 Owner's Manual

APPENDIX A: GENERAL INFORMATION

Many of you reading this manual have a lot
of experience in using mixers and mixing con-
soles. For you battle-scarred pros, Section 3
and the Block Diagram will probably be all
that you need to look at.
For those of you who are either new to
using mixers or just like to read even larger
quantities of our glib prose, we've provided
this short section that discusses the basic
concepts and procedures used in recording,
mixing and sound reinforcement work. If you
can make some sense of it, you can check out
your application and patching in Section 4
and start plugging things in.
Here is a primer covering a few important
ideas you should be on good terms with before
you sit down to a mixer.
LEVELS
Microphones have low output signals. Line
amplifiers have high output signals. One of
the functions of a mixer is to amplify or at-
tenuate these signal levels properly. Since it's
easy to degrade the signal by not handling lev-
els well, and since it's your hand on the knobs,
you should be sure you know how much gain
to apply and where to apply it. The Level Dia-
gram in Appendix E is a good place to start. It
isn't as complicated as it looks and is very
educational.
NOTE: No matter what combination of
cable adapters you may have at hand,
never connect the output of a power ampli-
fier to the input of a mixer.
NOISE
Every electronic circuit produces noise or
hiss or hash or buzz, and any noise present on
the input of an electronic circuit will be faith-
fully passed through. Turn it up high enough,
and you will hear the noise.
HEADROOM
Every electronic circuit also has a point of
overload, a clip point, where the voltage sim-
ply cannot rise any higher, no matter what the
input signal and your fader move would like.
This overload, or clipping, will show up as
tooth-grinding distortion.
Somewhere between the noise and the
clipping is an optimum level for your signal:
high enough above the noise floor to render
the hiss inaudible, and far enough below the
distortion point to allow range for loud peaks
of music to pass without clipping. This safe
operating zone might be called operating level
or nominal level or zero or perhaps line level.
The range between your operating level and
clipping is called headroom, which defines
just how tall your signal can be without hav-
ing to duck for the rafters.
Your mission as a designated Master of the
Levels is to get the low level signals up to line
level as soon as possible and to keep them
there as much as possible. But don't turn
them up too loud.
UNITY GAIN
If you haven't already, please read
"Important Sensitivity Adjustment
Procedure" on page 5.
METERING
A meter is an aid, a window looking onto
part of the dynamic range of your signal, and
it will tell you if your level is in the ballpark,
so to speak.
Try to keep your signals in the middle
range of the meters, for the most part. If the
signal is always very low, you may not be get-
ting the best signal-to-noise ratio you can. If
the meter LEDs are always solidly lit from bot-
tom to top, you are likely distorting both the
console and your recording tape regularly.
Keep the signal in the middle, around 0 VU.
Remember, the top yellow LED of the meter
represents a level of +10dBu, and the SR24•4
Appendices
39