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 iPad), 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:

• Master Controls, including group and main outputs (not always on separate faders), auxiliary masters, and EQ for these.
• Channel Controls, including allocation and routing, and EQ and effects selection.
• Return to Previous Menu. Then at least you will be able to get back from the Reset screen without deleting everything.

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?

...select/change 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:

• Faders and Fader Layers. Even large-format digital desks usually have more input and master channels than there are faders (for example, a desk with 16 channel faders may have 32 inputs). To accommodate the extra channels, channel faders are commonly accesssed in layers (some manufacturers describe theses as banks, while others describe fader sections as banks, so be sure you know which meaning is being used when looking at brochures or manuals). Layers are usually selected by means of buttons to the right or left of a fader section, so that (for example) you control inputs 1-16 by selecting Layer 1, and inputs 17-32 by selecting Layer 2.

  There is a trade-off between layers and the number of faders over console size: more faders gives you more working channels on each layer, while less faders gives you a more compact desk. Controlling a 48-channel band with 12 faders will mean constant layer-switching, which some engineers dislike, but whether you like it or not you will get more used to it in time. Bringing a 48-fader desk with you means you will probably need at least one extra crew-member to move it: the advantages of being able to carry everything you need in something little bigger than a suitcase are considerable. One potential problem in the multi-layer approach is that most of the desks that use it allow you to select a channel or mix on one layer and then move to another layer without de-selecting it. The point of this is that you can compare, copy/paste or assign channels and settings between layers. The disadvantage is that you can easily have something selected that isn't currently visible (making it relatively easy to apply changes to the wrong channel or mix). Manufacturers have different approaches to making you aware of which channel, mix or layer is currently selected, but some make it easier to see where you are than others.

  It isn't necessarily a choice between all faders or all layers, but it is usually advantageous to get all of a typical band on a single layer of faders, so desks with 16+ channel faders are generally easier to use. However (see Assignability, below), a compact desk with assignable layout may allow several practical workarounds, like adding all the drums to a single VCA or stereo group and assigning its control fader to the primary layer in place of the individual channels.

• Buttons and Knobs. In general, digital consoles have a lot less buttons and knobs than analogue desks, but there is a balance between having ready access and a knob for every function and having a clear and simple, well‑organised control surface. The advantage of having a couple of hundred selection points and control knobs (any of which - see assignability, below - can do almost anything) may be outweighed by the disadvantage of a very busy control surface. Conversely, the advantage of having fewer controls may be outweighed by having to change functions and layers every time you want to adjust anything. Getting this right is more of an issue in midrange small‑format consoles (which have more functions and better control than entry‑level products, but less space than their large‑format equivalents).

  On this aspect, particularly, it is useful to get some hands-on experience with a mixer before you buy it, as you will certainly find differences between manufacturers (and even between ranges from the same manufacturer) that will make one desk suit your own way of working better than another.

• Assignability. Large-format and higher-cost digital mixers generally have many more assignable controls and functions than lower-budget models, allowing a user to change fader layout and operation: the left-hand fader in layer 1 doesn't have to be channel 1 (and may not have to be an input channel at all), and any input can be assigned to any channel (so channel 3, which you have placed at the extreme right of layer 2, can control the input on socket 12). On lower-cost models, fader and channel positions are more often fixed, so that numbering corresponds with input sockets, as it would on an analogue desk (and, by default, on a fully assignable console).

  Being able to assign and locate anything anywhere you like on the control surface allows for considerable flexibility, but has its own drawbacks, principal among them being the fact that the same thing may not always be in the same place, which can impact severely on reaction-time in a live setting. It is also possible on most desks with assignable channels to remove a live channel from the control surface altogether, which may leave you hunting for a non-existent mute button (or worse).

  Other advantages include being able to use your own personalised layout (and transfer it, via USB stick, to other consoles of the same type), allowing touring sound-engineers to keep the same settings (assuming the same console is available) from venue to venue. However, assignability comes at a cost, and you may wish to consider whether you want to pay for being able to change the layout if in practice you will always have input 1 on channel 1 in fader position 1. Also, many lower-cost mixers with fixed primary layers also provide a ‘custom-layer’ (the Yamaha LS9 and Allen & Heath QU-series are examples), which allows at least a degree of flexibility for situations where an alternative layout may be required.

• Electronic Labelling. Most midrange or higher digital mixers have a small (usually LCD) label for each fader, allowing you to label individual faders using an on-screen keypad or scrollable alphanumeric selection, and even mixers without labels on the mixer surface often allow on-screen channel-naming. On compact desks channel-labels are typically limited to five or six characters, and generally don't get much longer even on large-format consoles, as names need to be large enough to see easily but narrower than a single channel-width.

  Some mixers also include a library of names (usually allowing user-additions), so you don't have to type KICK, SNARE (BASS, KEYS...) every single time you need them. Electronic labelling adds to the cost of the mixer, and you may find the ubiquitous strip of PVC tape gets it done more quickly. However, it comes into its own during changeovers, as the names can be saved with everything else during sound-check.

  The ability to name everything on the surface is of far greater importance if everything is assignable, and can be useful on any mixer. However, PVC tape has been used for channel-labelling as long as there have been channels (you can also use magnetic strips as an easily interchangeable write-on surface), and electronic labelling probably isn't enough on its own (although it probably won't be the only difference) to justify a substantial difference in price-point.

  It is also worth mentioning, however, that without (recallable) electronic labelling you may be able to recall all of the mixer's settings from an earlier session or event, but you won't know which instrument is on which channel unless you have kept a note of it somewhere.

• Display Screen. The two key screen variables are screen type and screen size.

  Most recent digital mixers have touch screens, and most users find these easier to use than those on older desks (for example, Yamaha's LS9) with button-operated menus. However, touch-screen sensitivity varies quite widely between manufacturers, and there is a trade-off between greater sensitivity (which makes them more prone to accidental presses or selections) and less sensitivity (so firm positive selections are required, which can mean you have to press the same thing repeatedly to get anything to happen). Many offer at least some sort of accuracy calibration or reset, which is useful. The screen surface is likely to need fairly regular cleaning, so ease of cleaning and sensitivity to scratching are worth thinking about: it is all very well for manufacturers to recommend avoiding solvents and only using a soft brush to clean surfaces, but even clean fingers leave a greasy residue (and fingers at events are not always clean) so a soft brush may be completely ineffective, while some solvents may damage the surface. ‘Baby-Wipes’ are usually fairly safe in an emergency, but check carefully before deciding to use one every time the mixer goes out. Mobile-phone screen-protectors may be suitable for some smaller screens.

  Larger screens tend to be the province of newer, larger and more expensive consoles, and the number of things you can do on-screen gets greater as size increases. Small button-operated screens are essentially display-only (you get a visual representation - e.g. EQ curve - of what you are doing, but have to implement changes using off-screen controls). Some of the smaller touch-screens (Allen & Heath QU-16 and QU-24 are examples) combine this with on-screen selection, but still require off-screen controls for changing most selected parameters). Larger screens generally allow much more on-screen control (for example, parametric EQ frequency, bandwidth and cut/boost can be adjusted on-screen on Allen & Heath GLD screens), as well as having higher-resolution graphics and the ability to keep more things in view at the same time. Some (see remote operation, below) allow you to use your own iPad or other device as a control surface, in which case screen size and sensitivity are not limited by the mixer.

• Digital Multicore and Stage-Box. Some of the lower-cost makes and models don't allow a digital connection (and some - usually older - digital mixers require an expansion card before you can use one). Larger-footprint mixers often have analogue inputs as well as a digital connection, while compact versions usually don't have enough space to allow a socket for each input, so require a digital multicore if you want to use more than a few channels.

  Having both options is ideal, as you can buy a digital mixer without having to replace your analogue multicore, and even if you do buy a digital multicore as well, you can keep analogue as a backup in case someone severs your cat-5 cable with a chair-leg.

  However, a digital multicore is easier to transport, install and connect, and although relatively expensive (generally adding anywhere from 10% to more than 30% to the cost of the mixer) is such a useful extra that you may regret buying a mixer that doesn't allow you to add one later.

• Remote Operation. Most modern digital mixers allow remote operation using an i-Pad (you'll commonly also need a wi-fi router), but those that allow Android or Windows notepads as well or instead are less common.

  This certainly brings some advantages (you can set up monitor mixes from the stage, or adjust the main mix and/or EQ from anywhere in the room), but can also be problematic: losing connection is one common problem, and being unable to see the screen in strong sunlight is another. Generally, therefore, remote access is very desirable (if not a requirement), but shouldn't be seen or relied on as a primary mode of operation.

  Another less commonly accessed aspect of remote operation is the ability to change and save mixer settings on a PC or other external device. With some (e.g. Digico mixers, which have a Windows OS) this is well-supported, and you can download an on-screen version of the mixer that is fully compliant with the mixer itself, allowing you to pre-program a show in your living-room. Even with those mixers that support it, you will need to be careful that firmware and software versions are the same on both PC and mixer. However, at the time of writing, support for this type of remote operation is patchy, so you need to look at manufacturer documentation carefully if this is something you would like your mixer to include.

• Recording and Playback. Most digital mixers will at least allow stereo recording in a digital format (usually using USB outputs, although S/PDIF or other connections are often supplied as well). Fewer - but still many - mixers allow digital multi-track recording and/or direct operation from a Digital Audio Workstation (DAW). If you intend using a mixer to make digital recordings, it is important to check its capabilities and available formats (see Compatibility and Upgradeability, below), as this is one area where you should not expect a simple universal plug-and-play feature-set.

  Most only allow recording in a relatively limited number of formats and resolutions (e.g. the Allen & Heath QU-series will only record 48-kHz 24-bit WAV files), so you should check for compatibility if you intend using your recorded tracks with other software.

  Most will also play recorded material from a memory stick or other external digital source, but many will only recognise a limited number of specific formats (some will only read WAV files, others only MP3, not many will read FLAC, and quite a few require a specific directory/file-path before they can see a file at all).

• Compatibility and Upgradeability. Digital Mixers use a variety of Operating Systems, and are not always configurable (indeed, are not usually configurable) to work with all other digital devices. Most allow interaction with i-Pads without major headaches, but interaction with other devices can be less straightforward. Drivers and software can be obtained for some common mixers and applications, but you should not assume you can automatically get it to work with your legacy version of Cubase or anything using Linux.

  Any mixer you consider should allow easy access to and installation of firmware and software updates, as this market is evolving rapidly and anything that cannot evolve with it will rapidly become obsolete.

• Rider Compliance. If you need a desk to meet the technical requirements of touring professional bands and/or their sound-engineers, you would do well to look at some up-to-date technical riders, and see what is being asked for (and what is being refused: it is no use having all the latest bells and whistles if touring engineers won't use the mixer). There isn't such a thing as a mixer that will please everyone, but a few - not always technically ‘the best’ - have very widespread approval.

More generally, you should check it has:

• All the Input and Output Channels You Need. Check that the mixer ships with them, as what looks like a bargain may not feel quite such good value after you have had to buy an expansion card and fit the extra connector panel.
• All the Correct Facilities. If you are going to need compressors, gates and effects, check both that everything you need is included (otherwise you may still need - but may not be able to interface with - an external rack), and that it is the correct type: if you need specific Lexicon effects, make sure they are included or can be loaded; if you need a compressor with side-chain capability or to use as a de-esser, make sure the installed compressor can do it (not all can); if you require four-band parametric EQ, check the top and bottom bands are fully parametric (not shelving-only, as they are on some budget desks).
• Total Save/Recall/Backup. Not all digital mixers can save and recall every single setting, and the absence of moving faders may not seem much of a sacrifice to begin with, but you may soon regret not having them. Ideally you should be able to save, back‑up and recall the entire console state quickly and easily. You will probably also find copying and pasting channel and other settings useful, so make sure copy/paste is available and simple to execute.
• Intuitive Controls and Layout. If you spend enough time with it you may get used to a poorly-designed console, but don't expect much sympathy from the band or the promoter if you can't get anything to work the first time you take it out.

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