Digital Mixers

Digital Consoles in Live Sound Reinforcement Systems

Digital mixers have been around for quite a long time now (early examples included Yamaha's 01V and 02R, and the Soundcraft Spirit 328), but they did not initially have much impact on mainstream live sound production.

More recent digital consoles have ironed out some of the early difficulties of combining extended and recallable functionality with rapidly accessible and intuitive controls, and some of the latest models from a growing number of manufacturers are quickly gaining acceptance and market share. Later digital mixers are less reliant on menus and have more of an analogue feel than their predecessors, and the balance in the professional live music arena has now moved from analogue to digital. Technical riders that once said ‘No Digital’ are now saying ‘No Analogue’.

What it is

It is a mixer in which mixing and sound processing are carried out in the digital domain. Analogue audio from the mixer's microphone preamplifiers is converted by analogue-to-digital converters (ADCs) into digital format. Signals are processed and combined by computer functions rather than by discrete electronic components, then converted back into analogue audio by digital-to-analogue converters (DACs) at the mixer's outputs.

What it does

Most of the latest digital mixers not only provide all the functions offered by their analogue predecessors, but also include banks of effects and processing that exceed the most comprehensively-equipped analogue offboard-rack. Channel functions commonly include four-band fully-parametric EQ (often with a choice of peaking or shelving on the uppermost and lowest bands), gating, compression, and multiple effects. In addition, there will usually be a generous provision of auxiliary sends (frequently with a 31-band graphic equaliser and/or multi-band parametric equaliser on all mixes and outputs). Most also include motorised faders (so everything, including fader positions, can be recalled at the touch of a button), and all but the least expensive makes and models include - or at least allow for - a digital ‘multicore’ and stage-box (placing ADC and DAC conversion at the stage box), so attaching the multicore to the mixer is via a single connection, and a 40+12 50-metre cable is little bigger than a domestic 50-metre 230V extension reel.

One principal facility that digital mixers offer and analogue mixers do not is the ability to store and recall settings. This allows you to store anything that you do repeatedly (for example, EQ-ing a Shure SM58) and recall it accurately and quickly. It also allows you to store and recall multiple settings (for example, console settings for an entire band), enabling, among other things, sound-checking and saving the settings for four bands, then recalling each band's settings for their performance. Digital mixers also offer considerable processing power (like compression and gating on every single channel) without the cost and weight of an equivalent offboard rack. Most also allow remote operation (so you can EQ the monitors from the stage with an i-Pad), and nearly all provide digital as well as analogue outputs (so you can take a digital - often multi-channel - recording, or connect directly to an amplifier with a digital input).

On higher than entry-level digital desks, also, channels are often independent of a physical control location: you can reorder them without needing to repatch on stage or at the mixer. Many also have more channels than their default stage-box has inputs, so that the same input can be routed to more than one control channel (allowing different mixes to be set up from a single set of microphones), which can make it much easier to manage shows with more than one band, or cover monitors and front-of-house with a single desk.

How it works

Essentially, it is a dedicated computer with an interface (control surface) optimised for live sound-processing. Typically, digital processing will deal with everything except input gain (and even this is under digital control), so that knobs and faders control processor functions rather than physical signals. This means, among other things, that a single knob or fader - like a PC's right-hand mouse button - can be context sensitive, and can be used for more than one task (or for the same task in more than one setting).

How do you use it?

If all else fails, read the manual! This may take some time: for example, the Midas PRO2 Quick Start Guide - to be fair it is multilingual - is a 40-page document.

In general, most of the actual functions control the same processes (and have the same effect) as their analogue counterparts, so if you understand all the components of sound processing from an analogue point of view your main challenge is to find out which knob does what. This isn't always helped by the fact that each knob or fader may control more than one function or channel, so you will usually need to select something before you can adjust it (putting you at least one button press - which button is it? - away from whatever you need to do). Commonly, a single control or section of controls for each function (for example, EQ) will operate on a selected channel or group. However, some controls are also commonly multi-function (for example, many mixers have a single parameter knob next to the display screen, and this will adjust whatever function has been selected on the active channel and/or mix), so you need to be aware at all times of which mix, channel and function is active. Some digital mixers are better than others at making the active selection obvious.

Even the most basic digital mixers generally have some sort of display screen (touch-screens are increasingly common), and having a visual illustration of what you are doing with EQ or dynamics can be very useful. Some of the larger touch-screens can give you most of an analogue console on-screen (you can expect having to toggle between channel and master sections), which can also make selection and operation clearer.

In general, however, you will probably need at least an hour or so to gain sufficient familiarity with any digital mixer to be able instantly to put your hands on the right function in a live environment. A mixer with an uncluttered interface that crams a lot of functions into a small footprint will typically rely more heavily on multiple-function controls.

If you are confronted with a digital mixer you haven't seen before and need to get operational quickly, concentrate on finding out what indicates selection and how to access:

Find out and make a note of the answers to the following (if you write it down, you are less likely to need to look at it later):

How do I...

...add (remove) a channel to (from) a mix?

...change channel volume in each mix?

...change channel EQ?

...change front-of-house volume?

...change front-of-house EQ?

...change monitor volume?

...change monitor EQ? an effect?

...add (remove) an effect to (from) a channel?

...change channel effect level?

...change overall effect level?

...add (remove) compression/gating to (from) a channel, group or mix?

...adjust compression/gating?

Do you need one?

If you already have a good analogue mixer with all the channels and offboard facilities you need, a digital mixer probably isn't essential. How useful its extra functions or save and recall capability will be depends on what you need your mixer to do, and you may wish to balance this against the loss of instant access to every control (although with most of the better current digital mixers you are usually only a single selection away from it).

However, if your event schedule includes (but is not limited to) repeat appearances by the same band, or regular returns to a specific venue or PA system, you will probably find the ability to save and recall multiple settings a considerable improvement on cue sheets.

If you are building a system from scratch, a digital mixer will typically cost less (and certainly weigh a lot less) than an analogue mixer with a well-equipped external rack. Also, it will have more processing facilities than the most comprehensively-equipped racks: you won't often see a rack with 48 channels of gating, 48 channels of compression, 16 channels of graphic EQ and eight effects units, and you certainly won't have room for one in the back of your car.

What sort do you need?

Most manufacturers have their own relatively distinctive hallmarks, so that feature-sets, layout styles and metering protocols remain brand-consistent from entry-level to stadium-class. All have advantages and disadvantages, as well as reviewers who will advise for or against them, but in general you probably won't go too far wrong with anything from the better-established manufacturers, including (in alphabetical - which means no particular - order) Allen & Heath, Digico, Midas, Soundcraft, and Yamaha. It is certain you will like some more than others, so it is well worth trying to get some hands-on experience before you buy one.

Some important variables are:

More generally, you should check it has:

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