Live sound - Live mixer

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The main difference between a live mixer and a studio mixer is the absence in the former of monitor channels and the monitor path, since these components are only needed in recording [Recording ] and studio mixing [Mixing ] . To simplify the following description, let's imagine a mixer which fulfils both the functions of a stage mixer and those of a FOH mixer. As we've said, it is possible to create a set of independent mixes for the musicians onstage. These mixes are created because of a greater number of auxiliary sends [Auxiliary send ] compared to studio mixers. An average-sized mixer can have more than 10 auxiliary sends, of which some will be used for the effects and the remaining ones will be used for creating the musicians' mixes[16 ]. So, with each channel's auxiliary sends we control the amount of signal in the mix, whereas the overall volume of each mix will be controlled by the aux send masters. Naturally, depending on the kind of mixer, a set of modules for the manipulation of the signal, such as equalizers, filters, compressors, gates etc. shall be present on each channel. Sometimes mixers, rather than having auxiliary sends, have a set of faders which function similarly to groups, in which each fader has the same function as an aux send master. The difference is that a master is piloted by a fader rather than an aux send master potentiometer. Let's also take a closer look at the way the groups are organized [Mixer: groups ] ; the latter can be of two kinds: normal or VCA. The normal groups work like the groups on studio mixers, namely, they group a set of input signals into one fader. VCA groups (Voltage Controlled Amplifiers) consist in an extra series of faders each of which controls a series of amplifiers that are present on the input channels, as shown in the following diagram:

Live sound - VCA controls

VCA controls

In the diagram we can see how in actual fact the signal in the channel isn't controlled by the variable resistance of the fader, but rather, by an operational amplifier whose gain is controlled by the fader. In other words, by lifting the channel's fader we don't act on simple resistance, as is the case with normal channels, but we modify the gain of the amplifier whose task is to control the signal. If we then transfer the control of one or more amplifiers present on the channels to a VCA group, the result will be that by acting on the group fader, we will control the level of all the channels that have been assigned to that group.

[16 ] Usually the mixes that are created are in mono, therefore each mix takes up one auxiliary send only. Sometimes it happens that a musician requests a stereo mix in front of him which requires two monitors.


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