So far we can balance and equalise. We can monitor by listening to what the audience hear through headphones. This does help as we can detect the onset of ringing much easier through headphones. What we cannot do yet is any form of monitoring what the audience cannot hear. We need some method of listening from a point in the signal path before the fader. In this case we can hear the channel even though the fader is still down and the audience cannot. This pre-fader listening ability (PFL) is extremely useful. It enable CD players and cassette decks to be cued to the correct tracks, it allows microphones in the wings to be checked before being faded up - all in all a most useful feature. Some mixers originally intended for recording studios sometimes end up as PA mixers. In most cases there are few problems but occasionally they have a facility very similar to PFL known as SOLO. This appears to work the same way, but instead of routing the selected source to the monitoring section, it simply mutes everything else - not a feature to be discovered half way through a show! The audience also find additional facilities useful. The main feature of almost all systems is their ability to amplify sound in stereo. This is not really stereo at all in the hi-fi sense, but merely a system which allows the apparent origin of a sound source to be moved across the sound stage from left to right. In the case of a music event the normal stereo mixing rules apply, but for very many shows the sound is virtually mono, with only sound effects being PANNED from point to point. The pan control, or to give it its correct title, the panoramic potentiometer, simply allows us to place the sound source anywhere between the left loudspeaker and the right loudspeaker. Even for music events realism is difficult as the loudspeakers are normally spaced widely apart. Normal recording techniques sound quite odd sometimes - consider miking a grand piano with two microphones for stereo. If the microphone at the bass end of the piano feeds the left speaker and the microphone at the other end feeds the right speaker we could have a piano over 20 metres wide! Imagine what that would sound like as the player went up and down the keyboard. For theatre we would probably leave the piano in mono and pan it to one suitable position and leave it. Stereo does of course mean twice as many amplifier channels. Although most theatres use two stacks of loudspeakers either side of the stage there are alternatives. The left/right approach works well for music, but speech is a little different. From the perspective of someone in the first few rows, close to the centre, the impression is that the actors voice is coming from somewhere else. It is, of course, coming from the far edges of the stage. To counteract this effect many larger houses in America, and more and more over here, are installing a split system. An extra 'cluster' of vocal range loudspeakers is flown centre stage, either just in front of the proscenium, or just over the apron (if fitted). This gives a central sound source for the audience to lock in on. Music and effects can still of course use the main left/right installation. Normally the mixing desk used has an extra mono fader group fitted which feeds just the flown centre cluster. The other main feature found on theatre type mixers is the auxiliary or send section. It is often necessary to send some of the individual channels contributions not only to the main output, but also to other devices for additional treatment. Normally this is some type of effect - reverb, echo or delay. The system used for these type of effects is to take the level that has been already adjusted by the channel fader (POST-FADE), control this amount with a rotary fader, and then group it together with similar sources from the other channels and then send it to the effects unit. After treatment the effected sound is then injected back into the mixer through the RETURN section. Most mixing desks also give control of overall return volume and left/right pan position and sometime EQ. Most desks also have provision for another similar send to that detailed above except that this time the sound is tapped off before the main channel fader (PRE-FADE). This time the extra output from the desk is independent from what the audience hear, and this signal can be returned to the stage (FOLDBACK), amplified and connected to loudspeakers designed for the performers to hear - not the audience. Singers, in particular do need to hear themselves, especially when the main PA system in use is quite loud. Most one night shows who do not tour with a PA of their own require the house to provide one of adequate quality. They will usually specify that it must have certain facilities. Very often the artistes consider the monitoring system one of the most important facilities present. Some may even require reverb to be included in the monitoring system. A good general purpose house system should be able to offer two separate, controllable channels of on-stage monitoring, independent from the content of the main house system. Normal usage requires one channel for the main artiste with the other used for the backing band. Even if the artiste is performing to backing tapes they will need the music through the foldback to sing to. It is a fact of life that many artistes spend more time on the monitor sound than on that for the audience. On small mixers the balance set on the individual channel faders is then combined into a left and right master output. This system is extended on large mixers by the introduction of grouping. Imagine the case of a rock and roll band. We may have 8 or more microphones just on the drum kit, plus a keyboard player with four or five synths. Even with enough channels available on a simple mixer, it would be difficult to raise or lower the entire drum kit or keyboard section volume without using all our fingers, and even this may disturb the balance set carefully at the sound check. Grouping enables us to direct all 8 drum kit faders to one or two group masters, which in turn feed into the main mix. In this way the drum kit balance can remain set while its overall volume can be simply raised up and down. In this case we may have groups set up in a similar way to this.

1. Lead vocals
2. Backing vocals
3. Bass
4. Guitar
5. keyboard left
6. Keyboard Right
7. Drums Left
8. Drums Right

This extra output approach can be taken even further with a number of extra outputs being available so that sound can be very precisely controlled in terms of destination. Very often these extra outputs are fed from the group outputs. A common format is that each of 8 groups can feed up to 8 separate outputs, this 8 X 8 mixing section being referred to as an 8 X 8 MATRIX