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Mixing with faders or gain controls?

There is a technique used by some operators where they set all the faders to ‘0’ position and balance the mix using the channel gain controls. We do not advise this method as the signal to noise ratio and control resolution can be severely degraded. In addition, it is impossible to mix monitors from FOH in this way as changes to the gain settings affect the monitors too.

The correct method is to use GAIN to match the source to the operating level of the channel for optimum dynamic range, and then use the FADERS to balance each source into the mix. With correct system gain structure, prime sources such as vocals would have their faders operated around ‘0’ while sources low in the mix such as backing vocals and acoustically loud brass and drums would display their true contribution with their lower fader positions. This is a much more visual and accurate way of mixing.

Mixing the PA in mono or stereo?

Because a console provides an L and R output does not mean you have to mix in stereo. It is often convenient to have separate fader control, processor inserts, and outputs to drive two mono speaker stacks in an FOH system. How much stereo you introduce into your mix depends on where you position the pan controls. In most situations the size of the room and position of the speakers makes stereo mixing an advantage only for a small section of the audience, usually those around the sound operator! Those listening near the speakers are likely to lose information from the opposite stack. For this reason it is best to mix most sources in mono (pan centred). However, it can enhance the image by mixing some ‘ambient’ sounds in stereo, for example reverb returns, keyboards and special effects. Where the speakers are widely placed, you can reduce the stereo image by reducing the amount of panning to each side. Whatever image you create it is important that you listen to the results and consider the listeners at all positions in the room.

Zero the console Before starting the sound check

it is good practice to ‘zero’ the console by setting all its controls to a sensible starting condition. Check that the mode switches are correctly set for your application. Set all GAIN, EQ and PAN controls mid, FADER, AUX and MATRIX controls off, TALKBACK and OSC/NOISE levels off, and all switches up.

Turning the system on and off

It is good practice to:

Turn the amplifiers on last and off first.
Mute channels before plugging cables, unplugging instruments and switching phantom power.
Let equipment which has been stored in a damp or cold place acclimatise in the venue first before powering it up.
Power up the system in plenty of time before you start the sound check or show.

Sound levels

The ear is a delicate instrument. Do not subject yourself or any listener to long periods of loud sound, particularly with extreme equalisation. This may result in frequency selective or full range hearing loss. Adhere to the sound level regulations which may apply to the venue… and common sense!

Mix and Aux-Fed Subs

Driving the PA system sub bass speakers with their own mix has two main advantages. First, the mix is much cleaner because only sources that generate the low frequencies, for example kick drum, bass guitar, keyboards and sound effects are sent to the subs. Low frequency bleed from these sources into open microphones such as vocals and snare is eliminated from the PA much more effectively than using just the channel filters. Second, the sub bass amplifier is only working with the sources needed. It is not wasting power reproducing unnecessary pickup.

The subs can be separately driven in several ways. A common method is to use the independent M mix. Route all sources to L-R. Route the sources you want in the subs to both L-R and M. Feed the LR to a stereo crossover to drive the top speakers, and M to a mono crossover to drive the sub speakers. Refer to the speaker manufacturer for recommended crossover frequency, usually within the range 80Hz to 120Hz. The PA overall level is adjusted by moving the L, R and M (sub) master faders together.

Another method that has become popular is to use an Aux mix to drive the subs. This is referred to as ‘aux-fed subs’. Align the system so that the normal unity gain position of the channel fader and aux send result in the correct speaker balance. For sources you wish to send to the sub, turn up the channel aux send to its unity 3 o’clock position. Avoid the temptation to ride the aux send to create more or less sub as this may upset the natural speaker balance or cause problems for listeners in different parts of the room.

One problem with using the aux in this way is that it becomes difficult to balance the top and sub speakers if you need to adjust the overall volume of the PA. Typically the LR (tops) use fader masters, and the aux is on a rotary master.