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Complex productions often will combine several different audio inputs
- microphones, CD players, tape decks, etc. A way to manage all of
these inputs and combine them so they can be played out of a single
sound system is clearly necessary. This is where the mixing
board (also called a sound board, mixer, or mixing
console) comes in.
A 14-input mixing board, manufactured by Mackie Designs,
Inc. Small boards such as this are offer plenty of capability for
most theatre shows, and should be used in place of large boards where
The overall job of a mixer is to take several inputs and combine them
into a small number of outputs. Generally many features are
offered, such as adjustable equalization (the changing of the
tone of a sound), volume level adjustment, and muting. Mixing
boards can be quite complex, and there are many differences in
operation between models.
Mixers are generally referred to by the number of input channels
and output channels they have. An input channel is a place
where a single audio signal can be connected into the sound board. An
output channel is a path of exit from a sound board for an audio
signal. Mixers with four, eight, twelve, sixteen, twenty-four or
thirty-two input channels and two to eight output channels are not
uncommon. On these boards, each input can be assigned to an output,
with the options of assigning several inputs to one output, and one
input to several outputs.
The typical elements of an input channel on a mixer. This is
representative of a relatively small mixer. Larger boards usually
have a larger equalization section, more aux sends, and output channel
Input channels typically allow for the connection of a microphone-level
signal or a line-level signal such as that from a CD player or tape
deck. Microphone-level signals are very low-level, on the order of
millionths of a volt. Line level signals are in the range of a tenth
of a volt to two volts. This discrepancy in levels is one of the
reasons that most mixers have two types of inputs. Typically these
inputs are chosen with a small pushbutton or toggle switch, as only
one may be used at any given time. Most mixers allow for some sort of
trim adjustment, to normal the level of the signal as it enters
the board. This is necessary because different microphones and pieces
of equipment have slightly different output levels. The trim
adjustment allows the board operator to make each input appear to be at
about the same level so that the differences can be ignored once the
board is set up properly.
Each channel on a mixer typically has what are referred to as
auxiliary sends (aux sends). It is common to find one to
eight aux sends on a sound board. Each send typically has a knob
associated with it on each vertical channel strip. The knob controls
the level sent to that particular aux send. Aux sends can be thought
of as board outputs with individually adjustable levels. Typically
aux sends are used to send some of the input signal to an effect such
as reverb, but they can be used creatively for other purposes.
Generally, each channel has some form of equalization (EQ)
is, controls to adjust the tonal quality of the sound. Small mixers
may only have adjustments for bass and treble, while larger boards may
provide bass, treble, mid-range, and adjustable range controls. These
adjustable range controls are called parametric equalizers, and
allows the user to choose not only to boost or cut a frequency range,
but to choose which range to work with. Equalizer controls function
much like the familiar bass and treble knobs found on stereos. It is
common to use an equalizer to improve or alter the sound of an input.
For instance, removing bass from wireless body microphone inputs can
reduce annoying ``clunking'' sounds that may be picked up from the mic.
Most mixers are capable of handling stereo signals. A system is
considered stereo if it has two discrete signal paths in the final
output stage (i.e. the left and right speakers). Since each input
strip is mono (on most mixers, anyway), the board provides a pan
control to adjust the ``position'' of the mono sound between the left
and right channels. The signal can be panned anywhere from full left,
to center (both channels), to full right. This is an extremely useful
feature, as it can make for more realistic effects. For example, if a
sound is supposed to be coming from one side of the stage, the pan
control can be used so only the speaker on that side is used.
It should be noted that on boards that have multiple outputs, the control
is usually set up to pan between even and odd sets of outputs. For
example, hard left really means output channels 1, 3, 5, etc. The
manual for a sound board should always be consulted to see how this
feature is implemented to avoid any unpleasant last-minute surprises.
The most prominent part of a mixer is probably the set of channel
faders, generally located at the bottom of the board. Most
mixers use linear style faders (also called sliders), but some use
rotary knobs. Regardless of the style of control, they all perform
the same function, which is controlling the level of the signal sent
to the outputs of the mixer. On large boards, the output select
switches are usually positioned near each channel fader. These
switches allow the board operator to set which output channels each
input gets routed to.
Lastly, two buttons commonly found on mixers are the mute and solo buttons. Mute, as its name implies, silences the input signal.
This is very useful in situations where there is noise on an input
(such as someone chatting near a microphone) that is not desired at
the outputs (or ``in the mix'', as it is called). The mute switch
allows the faders, which may be set at an important level, to be left
alone when silencing an input. The solo switch, found in many
different forms on different boards, allows a signal to be listened to
by itself. Often this can be routed to a pair of headphones, which is
an extremely useful feature for cueing tapes, etc.
A 32-input mixing board with eight discrete output buses,
manufactured by Mackie Designs, Inc. This particular model of
mixer is owned by WPI, and is often used for large theatre shows.
The mixing board is a key element in the sound system, and knowing how
to use it properly can go a long way towards making the sound effects and
music of a production sound good. While most mixers function
similarly, there are always small differences between boards. These
differences sometimes are very obvious, but sometimes they require
reading the manual before they become apparent.
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