OK - here's the situation. You're sitting in front of a studio mixing desk,
and you are feeling
utterly daunted by all of the knobs, sliders and buttons in front of you. You think
that anyone who can operate one of these things must be some sort of superhero.
Not so. e-troon's Guide to using a mixing desk will reveal the secrets, and give
numerous tips and tricks.
Structure and function
A mixing desk is designed to take lots of input signals, and mix them all together
into one or (usually) more output signals in a controlled fashion. A typical desk will
have between 8 and 96 input channels, with a strip of knobs, buttons
and a slider (fader) for each channel. All you need to learn is what one of these strips does,
and you know how most of the desk works.
Imagine the signal coming in at the top of the strip. This usually isn't hard, as
it quite often actually does connect at the top of the strip. It then works its
way down, getting manipulated on the way, and then through the fader (slider).
The output from the fader goes across the desk to the master section. It
may also get split up and move across at various points down the strip - see the
section on auxiliary send outputs below.
Input types and the gain control
There are two main types of input signal: balanced microphone / DI box
level and unbalanced line level signals. Often, a good desk will have
an XLR input for the mic signals and a jack socket for the line level signals. Occasionally, desks intended for disco use may have an RIAA phono input for connecting a record deck. Each channel is usually monophonic, so you'll need to use two channels for a stereo input.
You may find an additional "insert" jack - this is a "stereo" jack socket into
which you can plug external units such as compressors that you want to act on that
channel only. It's basically an "out-and-back-in-again" socket.
The topmost control on most mixers is the gain control. This is where you can set the
level of the incoming signal to be roughly equivalent across all the channels. For
example, two different types of microphone may have different output levels
(or you may have a quieter singer!): you can use the gain control to balance the two so
that the fader settings (see below) are independent of this difference. The intention
is that this is set up for each session and then not adjusted again.
EQ is like the tone controls on non-purist hi-fi systems. Typically, a desk will
Use these sparingly, to tune the overall sound of each channel. You will find that
setting up each channel to sound as good as possible will not result in the best
mix when all the sounds are combined. Pick out the essential frequencies of each input
and emphasize those, cutting anything extraneous or confusing.
The parametric controls aid reduction of feedback - you can "tune out" the frequencies
that are feeding back by applying a bit of cut, and sweeping the frequency control until
the ringing or feedback is suppressed. This method won't compensate fully for poor
acoustics or positioning of microphones and speakers, but it helps. There is a fine
balance between reducing feedback and ruining the sound with excessive controlling EQ.
Many desks also have a low-pass filter which effects a sharp cutoff below 100Hz, to reduce thumps and hum. Obviously, don't use this on any input that has useful content below that point (bass, guitar, piano etc).
Most desks have a number of auxiliary outputs. These can be used to provide additional outputs for foldback, recording, hearing-aid induction loops, effects etc. Some aux
sends are of the pre-fader type, where the setting of the main fader does not affect the
output of the aux send (think parallel);
some are post-fader, where the output is affected by the fader (think series).
This information may or may not be marked on the desk. Some desks have both types
of aux send.
For example, if I connect AUX1 to the foldback system, and it is a pre-fade aux send,
I can provide a completely independent mix to the foldback, totally unaffected by the
main front-of-house mix, which is controlled by the main faders. For a reverb unit,
it would be preferable to use a post-fade aux send, as you would want the output from
the unit to be proportional to the main fader setting.
The Pan setting determines "where" this mono channel is positioned in the main stereo output, and can be set from 100% left to 100% right.
Subgroups and master output
Many desks have one or more subgroups, which act as an intermediate "pre-master" for a
subset of channels. You'll probably find a few buttons allowing each channel to be
"assigned" to any of the subgroups and/or the master. For example, you could mike up
each of the drums in a kit, and group all of these together on to a subgroup. The faders on this subgroup can then control the entire drum kit level without having to adjust
ten separate faders.
PFL / AFL
There may be a couple of other buttons labelled PFL and/or AFL. This stands for pre- and after-fader listen, and feeds that channel to the desk's headphone output. Useful for tracking down a problem channel.
Push it away from you to get louder, pull it towards you to go quieter. Typically, the fader will have a scale of minus infinity to +10dB. The intention is that the gain control is set
so that the "correct" level has the fader at 0dB, giving a bit of headroom to turn it up if necessary, and plenty of downwards adjustment for smooth fading. Following this philosophy will
also ensure that the signal levels in the mixer are optimum for best signal to noise ratio.
I'm going to add tips and hints at a later date. If anyone wants any more information on any section, /msg me and I'll endeavour to add it.