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a novice engineer's guide to what all the knobs and switches on a mixing-desk do

Mixing consoles have a lot of knobs on them because they need them. And if you're going to mix your music properly, you need to know what they all do. Finding out is easier than it looks.

BLIMEY, WHAT A LOT of controls. Do you know what they all do? If I had a penny for every time someone asked me that question after seeing my mixing console for the first time, I'd now have, well, at least 48p.

But there's no getting away from it: mixing consoles do look incredibly complicated. The good news is that they are fairly logical if you take them a piece at a time, and the aim of this feature is to acquaint you with the more important features of mixing consoles, so you can at least make intelligent-sounding comments the next time you casually lean on one.

It doesn't matter whether the mixer is large or small, or for that matter whether it is designed for PA or studio use; the underlying principle is exactly the same. Essentially, a mixer takes several audio inputs (such as microphones, synths or outputs from tape machines) and allows them to be combined in an artistically pleasing manner. At its simplest, you could have a mixer with (say) four audio inputs, four volume controls and a single mono output. This would be called a "four-into-one" mixer and would give you control only over the relative volumes of the individual sounds. Not all that hot, you might think, but the earliest Tamla Motown hits were produced on mixers that were this basic, and simple four-into-two mixers, which are just stereo versions of the same thing, are the preferred type for today's nightclub and hip-hop DJs.

But because almost everything we hear now is in stereo, a mixer with just level controls is no longer adequate for most people; we also need "pan" controls so that the individual sounds can be moved to any point between the speakers.

Diagram 1

Diagram 1 shows how a very simple four-channel (four-input) mixer might look. Notice that I've also drawn in a master volume control, which would enable you to turn the overall output level up or down without having to change the level settings on the individual channels. The two outputs carry the signals for the left and right sides of the stereo mix and, would usually be fed to an amplifier and speakers, although many mixers allow you to plug in headphones so you can hear what you're doing that way.

And so to our first piece of technical gobbledegook: "equalisation". This is something studio engineers and PA operators are always talking about, but it's often abbreviated to "EQ" and is only a flash term for "tone controls" anyway. In the good (?) old days, amplifiers and mixers often had just a single tone control that made the sound brighter or mellower. This was soon replaced by separate bass and treble controls, and the reasoning behind the change was fairly straightforward - the treble control allows you to increase or decrease the amount of treble without affecting what's going on at the bass end, and vice versa. Pretty soon after that, someone decided that a separate control for the "midrange" would be nice, and before long equalisers had grown dozens more knobs and buttons which allowed them to be more selective in operation. And just so you don't have to put your audio signal through unnecessary circuitry, there is now often an "EQ bypass" button which sidesteps the tone circuitry completely if you decide you don't need to make any changes.

So, rule one is simple. Remember that when anyone tries to impress you with details about equalisers, they're just talking about a tone control. A mighty fancy tone control, perhaps, but a tone control nonetheless.

To keep the layout of the average mixing console logical, the front panel is usually divided into vertical rows, each row carrying the controls required for a single input or channel. If you look at any big mixer, you'll notice that all the input channels are exactly the same - so learn one and you've learnt them all. But even with the fancy tone controls, there are still lots of knobs or buttons that haven't been accounted for, so let's look at a few more.

Any serious mixing console has to be able to handle a wide range of input signals: from the tiny electrical output of a microphone to the relatively hefty output from a tape recorder. So, you'll almost certainly find a "Mic/Line" switch somewhere near the top of each channel. Next to this will be a "Gain" control so that whichever signal level is plugged in, it can be adjusted to the correct level for the rest of the mixer to accept. This process is sometimes called matching - remember that term if you want to look (and sound) cool.

Another impressive term which you normally find written next to a button near the top of a mixer channel is "Phantom Power". This sounds utterly wonderful and very mysterious, but it's really a simple system for feeding 48V of power along the cables to any microphones that need power - such as condenser mikes.

You may also see a microphone "Pad" button, which is actually used to reduce the signal from the microphone if it happens to be too high for the mixer - as it might be if you have a particularly efficient mike next to something very loud like a bass drum. Think of it as the electrical equivalent of a pillow between your ear and a pneumatic drill.

Moving down the channel, you might find some more knobs labelled "Auxiliary". These don't look much, but are quite astonishingly useful. For a start, you can use them to set up a separate mono mix of your inputs which can then be fed to headphones so that the musicians in the studio can hear a balance which suits them. For example, the bass player might want a mix which has the drums high up so he can keep time. The Auxiliaries used for this are called "pre-fade" because they work independently of the channel's main level control, and you may also find them labelled Monitor or Foldback.

Auxiliaries are also used for adding effects to music, though for this you'd use the "post-fade" Auxiliaries, sometimes called Echo Send or Effects Send. Again you're setting up a separate mix, but this time it is affected by the main channel level controls, for fairly obvious reasons. If you have echo on the lead guitar, for example, and you turn the guitar down part way through the song, you'd normally want the echo effect to go down by the same amount.

The number of different Auxiliaries on a desk may vary from none at all up to a dozen or so, and their pre- or post-fade status may either be fixed so that you have some of one type and some of the other, or there may be a switch by the control so that you can decide which you want. The more pre-fade Auxiliaries you have, the more separate mixes you can set up for the musicians' foldback or monitoring system. On the other hand, the more post-fade Auxiliaries you have, the more effects units you can use. Remember, though, is that the Effects sends or Post-fade sends don't actually create any effects - they simply create a mix which feeds into an external effects unit such as a reverb unit, echo machine or whatever. The output of the effects unit is then brought back into the mix using a special section called Effects Return, which is really the same as an input channel but grossly simplified. Typically, an Effects Return may have only a level and a pan control, so the overall level of the effect can be controlled along with its left/right position in the stereo mix.

Well, we're nearly at the bottom of the channel now. On a more basic desk, you'll have one or two Auxiliaries followed by the channel fader. This is the same thing as the level control, except that we now use a slider instead of a rotary control simply because it's easier to adjust, and you can see at a glance where it's set.

If you look at a studio desk, you'll also find a lot of extra buttons in this area and the reason behind this is quite simple: in the studio, a mixer has two jobs to do. When you're mixing sounds that are already on a multitrack tape recorder to produce your final stereo master tape, the channels are all routed to the left and right mix outputs, depending on the individual pan control settings. But before you can mix, you have to make the recording - which is where the other buttons come in. Your multitrack tape recorded may have up to 24 different tracks, each of which can record a different sound, and the mixer's first job is to get the right sounds onto the right tracks of the tape recorder. To do this, there are additional routing buttons that correspond to the tracks on the recorder, so that you can route any mixer channel to any tape track. Instead of having 24 routing buttons, many mixers have only 12, each of which can access two tape tracks. The pan control is then turned fully left or fully right, depending on whether you want your signal to go to the even-numbered tape track or the odd-numbered one.

Believe me, it's a lot simpler than it looks in print. On the right-hand side of most desks you'll find extra faders (known as Group faders) corresponding to the tape input tracks. These are effectively master volume controls allowing you to adjust the level that goes to tape. For example, you might have eight drum mikes occupying the first eight mixer channels, but these can be mixed and routed to just two tape tracks, to give a stereo drum mix on tape. Group faders one and two could then be moved together to control the level of the whole drum kit mix fed to tape.

Other channel buttons include the Mute switch, which turns off the channel (including effects) when not needed so you can switch an instrument in and out of the mix as required. There's also the "PFL" or Pre-Fade Listen button, sometimes called Solo, which allows the engineer to hear just that one channel in isolation over the studio speakers - useful if you're trying to track down an elusive hum or buzz.

Diagram 2

The left-hand side of the console normally comprises the input channels, and as we've said, these are all identical. Diagram 2 shows a typical input channel so you can find your way around.

The right-hand side is reserved for the Master section which includes, as we've already said, the Group faders which regulate the levels being fed to the multitrack tape recorder. These can also be used when you mix to control several mixer channels from one group fader: working like this is called sub-grouping. A typical application would be to mix all your backing vocals (which might be spread over several tape tracks) to one or two subgroups so you can control the overall backing vocal level using just one or two faders.

On a recording desk, you will also find a Monitor section, which is really a mixer within a mixer - allowing you to set up a rough mix of the sounds already on tape for the benefit of the musicians recording new parts. If you think about it, you couldn't record any new parts without hearing the parts you'd already recorded, because you wouldn't know whereabouts you were in the song!

The Effects Return controls usually reside in the Master section, along with all the other useful odds and sods that don't fit anywhere else. There's the test oscillator, for example, which provides tones used in the calibration of the tape machine, and there's often a "talkback" mike so that the engineer communicate with the musicians in the studio. There may even be provision to select more than one set of monitor speakers, so you can hear your mix on a pair of domestic speakers to check compatibility, and so you'll be able to play your master stereo tape back via the mixer without having to unplug any cables. This is important, because the mixing console is really the control centre of any studio, and it's vital that signals can be routed wherever necessary without having to keep plugging things in and out.

However, where things simply must be plugged in and out - such as effects units and processors - the relevant connections are usually brought out to a patchbay so that connections can be made using short patch leads, just like in the old-fashioned telephone exchanges.

Now, next time you go into the studio or hire a PA rig, you should at least be able to say things like "that's a pretty basic EQ, isn't it?", or "do you find that two pre-fade auxiliaries are really enough?"

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Unexpected Repercussions

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The Human Side Of House

Phaze 1 - Copyright: Phaze 1 Publishing


Phaze 1 - May 1989



Feature by Paul White

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