Mixing for the Small Gig (Part 2)
What the knobs mean on the average desk, and which ones kill.
More map reading in mixer land. Ben Duncan forges ahead with his guide to knobs and buttons on the average desk. It begins to make sense...
WHEN YOU'RE next at a big gig, have a look to the side of the stage, and you'll see a 'monitor' mixer in addition to the main out-front mixer. This monitor mixer can be as much as 30 grand's worth of electronics, and all so the players can hear themselves.
But we don't necessarily need one: we're going to concentrate here on making do with existing equipment. Because even the most basic PA mixer will have one or more Monitor Sends on which we can create a mix for the monitor speakers up on stage.
First, though, let's straighten out the terminology. The Monitor Sends are sometimes called 'fold-back', a weird BBC-sourced word more suggestive of what happens when the 20 stone humper leans on the keyboard's flimsy stand. As for the knobs themselves, they are commonly called Auxilliary Sends but are more typically (and confusingly) labelled either Pre and Post, or Aux 1, Aux 2 and so on.
Your mixer might have two, three or four Aux controls, but they won't all be suitable for producing a monitor mix (because the output to the stage monitors has to be irrespective of each channel's fader settings). So the only ones we can easily use are the Pre-fader Aux knobs; these are the lower numbers, eg Aux 1 and 2. The remainder — the higher numbers, say Aux 3 and 4 — take their signal after the channel fader, hence 'Post-fader', and are for effects (which we'll shorten to 'FX', and about which more later).
If your mixer has just two Aux knobs (Aux 1 and 2), Aux 1 will be the one to use — meaning just one monitor mix (bah!). On more elaborate mixers with four Auxiliaries, you can often switch the Aux 2 and Aux 3 knobs between Pre- and Post-fader duties. So, assuming Aux 2 and 3 aren't needed for FX, we can switch them to Pre-fader and then go on to make three separate monitor mixes.
To set up a single monitor mix, find out what the players want/need to hear, get it down to the bare essentials, and wind up the Aux 1 knob on the appropriate channels. To hear what's going on (on your cans, or headphones) you'll probably have to press a button marked PFL (Pre-Fader Listen) on the relevant channel. The overall level sent to the stage is controlled by a master Aux knob in lieu of a fader, and it's usually placed on the right-hand side of the mixer.
With elementary stage monitor systems, howlround (feedback) is a common problem. The cure is to keep to the minimum the number of Aux sends going at full bore. If one instrument has to be turned up, others, less essential, will have to be turned down.
When there's a howlround, don't panic. Your mixer should have little red overload LEDs, which will come on to reveal the guilty channel(s). Then you can slam down the appropriate Aux knob(s) and bring them gently back up to the point just below where the howl starts again.
The one essential FX unit for PA is reverb/echo. Of the Aux sends discussed above, we need the Post-fader variety. If there are just two Aux knobs, it's Aux 2. On older mixers, it'll be labelled 'Echo' or 'Reverb Send'.
This is a bypass scheme: a clone signal goes out of the channel's Post-fader Aux output, into the FX box-of-tricks, then comes back in via the socket marked Effects-Return or Aux-Return, so it can mix back in with its unprocessed partner. Failing this, you can feed the FX output into a spare channel (if any).
Confusing? It may help you to think of the send and return jacks on the back of a guitar amp: the external signal undergoes the full FX treatment, and is then mixed back in with the clean signal (which has meanwhile passed intact through the mixer's normal pathways) to create the degree of FX required. If there's a dry v. FX balance control on the FX unit, turn this hard-over to effect; you can then get the FX balance by concentrating on the mixer's knobs alone: turning down the Aux 2 knob (say) makes the signal drier.
If the FX distort(s), check whether there's an input level control or mike/line switch, or else a choice of hi/low sensitivity input sockets.
Having set up the drum sound by balancing the various drum mikes, it can be a panic to adjust the overall drum level since it's no easy task to keep all the various faders exactly in their relative positions whilst shuffling the whole lot up or down. If by some miracle we'd managed to balance the kit with all the faders at (say) setting 7, the problem could be simply solved with a ruler or bit of wood.
Failing this, the 'subgroup' comes to the rescue.
Subgroup faders now appear on quite small mixers. They're invaluable for live work, since they allow related channels to be controlled as one. In general, there's a button or switch on each channel (just below the Aux knobs), to route (direct) the signal to one of the four, six or eight subgroup faders, and another switch adjacent to these to route all the subgroups on to the usual pair of (stereo) output faders. Having selected Group 1 for all the kit's channels, the first subgroup fader on the right of the mixer now lets us control the whole kit's level: look! just one finger. Other possible candidates for subgrouping are vocal and brass sections — it all depends on the band.
The channel's Pan control sweeps the output between the left and right sides of the PA; it's much the same as recording. Conventionally, the players are panned (ouch!) according to the visuals, so the bassist comes out the right-hand PA stack, drums central, or whatever. Tricks include putting echo to the left, and dry signal to the right, but don't go overboard. Remember people standing near the left-hand PA stack have also paid to hear the gig.
Most booms, howls and squeaks arise because there's too much level at the frequency of the boom, howl or squeak. Commonly it's the fault of the speakers, the mikes, and the acoustics of the venue: all of these can arbitrarily boost certain 'spot' frequencies. Without billions of pounds to spend on speakers and mikes with a flat (even) response and on refined 27-band graphic equalisers, there's still room for some fine tuning.
First, the frequency of the boom, howl or squeak tells us which frequency needs cutting out. Knowing that the overload LEDs on any channels which are feeding back will be glowing RED, you can now quickly spot both the guilty channel and the EQ knob to turn down. For example, if there's a sudden "boooooooom", that's a bass howlround, so we turn down the bass EQ on channel... ah, channel 6's overload LED is red... the bassist.
Secondly, if the howl is in the midrange and your mixer has a midband sweep EQ (tuneable frequency marked in Hz or kHz), you may be able to retain most of the chosen EQ by sweeping a bit higher or lower. This works because we've shifted the main boost a bit above or below the critical howlround frequency, hopefully without loosing out too much of the instrument's chosen EQ.
Lastly, we've already discussed positioning of players and monitor speakers. When howlround threatens, we'd also better beware of the position of the PA stacks. They mustn't point inwards towards the stage, and should ideally be well forward of the band. This might mean moving the whole set backwards if it's been over-enthusiastically set up forward of the PA speakers, or if the PA's sound dispersion is spreading backwards, or is being reflected straight back at the stage.
Feature by Ben Duncan
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