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

EQ is like the tone controls on non-purist hi-fi systems. Typically, a desk will have:

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).

Aux sends

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.

Pan

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.

Main fader

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.

The faders on BBC mixing desks customarily work in the opposite direction to other desks. You push the fader away from you to get quieter and pull towards you to get louder. This can obviously cause confusion for people working in more than one radio station.

Originally, all mixers were in the up-is-quieter format, with the SSL 4000E probably being the first to reverse the trend. While other manufacturers followed the 'new way', the BBC still have some examples of the older form.

The traditional (and possibly accurate) reason given for this is that if the presenter falls asleep on the job and slumps forward, they will effectively mute the output, rather than blowing everyone's ears off.


Source:
http://www.studio-sound.com/archive/july99/celeb_mix.html

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