Audio Mixers

The Analog Mixer

Mixers are the large-format equivalent of the computer interfaces we’ve discussed earlier; they’re the routing center for a PA system. Analog mixers are quickly becoming a thing of the past, but there are still plenty of schools and venues who haven’t invested into digital technology.

The basic unit of a mixer is the channel strip. It has a single input (or stereo pair of inputs), an input gain pot (stands for potentiometer), a bunch of EQ and routing options, and a volume fader. The smallest mixers only have 1-4 channels, while the large-format consoles can have dozens of banks of 32 channels each. Once you learn one, you can step up to almost any mixer and know what you’re doing. Here’s an example of an analog mixer (with most channels cropped out, but they’re identical to the two you see here).

A Behringer analog mixer with labeled parts

Running a Mixer

Step 1 — Plug everything in: Mics and DI inputs go into the XLR jacks on each channel. A channel can only handle a single, mono source; if you have a keyboard with two DI boxes, for example, it’ll take two channels. Most of the time, a line-level source will go into a dedicated, stereo channel (the last four channels in our example).

Outboard gear goes into the FX sends/returns. Speakers, monitors, and headphones are each plugged into different outputs—main into the main outs, monitors into the aux sends, phones into their own jack.

Step 2 — Set the gain: This is perhaps the most important step. At the beginning of the sound check, with each fader set to -0- (nominal), have each player perform the loudest part of their program. As they play, raise the gain from -∞ to where it begins to clip, then lower it a little to allow for some wiggle room. Distortion and feedback usually result from the gain being set too high. Keep an eye on levels and feedback during the performance, since performers generally play louder during the actual show, and the room full a bodies will respond differently than during the sound check.

Step 2 — Set up Monitor Mixes: As the group plays through some songs, they’ll give you direction on what they want to be sent through the monitors; this is usually accomplished via the aux send pots, and sometimes utilizing group sends. Some mixers offer complete flexibility, and other send the same things to every monitor. With skill, gear, and luck, you’ll hopefully get monitors mixes that satisfy everyone and don’t lead to a muddy, feedback-ridden mess. Large shows usually have a dedicated monitoring engineer with his own mixer and in-ear monitors.

Step 3 — Set Up Effects: As the performers play through some pieces, use the solo switch to hear each channel individually in the headphones. Engage the high-pass filter on most, if not all, channels. Tailor the EQ to taste. Use the Au/FX knobs to decide how much of each input to send to each effect. Often, there is a multi-effects processor for one or two additional effects (like reverb/chorus/delay).

On a digital mixer, selecting a channel brings up a large host of possible effects and dedicated, multi-parameter knobs for the most common ones (parametric EQ, compressor, gate). Digital encoders that can be mapped to hundreds of parameters are used to control uncommon or complicated effects (like a digital reverb).

Step 4 — Get a Mix: Hopefully, you’re in a location that gives you a good idea of what the audience will hear. If not, walk around; this is easiest if you have a digital mixer with a wireless controller since you can alter parameters from anywhere in the house.

Additional, Advanced Step — Tune the House: Hopefully, you’ll have enough time before the show to get a feel for the venue. Play some music you know well or have hand-picked for tuning systems, or use audio waves designed for this very thing (sine sweeps, pink noise). Set up levels and an EQ curve that deals with some of the room’s trouble frequencies so you have less guesswork during the sound check. If it’s too late, you may have to deal with some of these issues on-the-fly. A concert I did at a high school had a house system that had fallen out of tune enough (probably due to students’ meddling) that I had to bring in a different system and bypass the house entirely.

The Digital Mixer

The first digital mixers were basically copies of analog mixers with some form of digital conversion in the signal path. Over the years, they have become almost completely different, with features and price drops that make them a no-brainer for just about every situation. Prices have fallen about 40% from 2014 to 2017 in the budget-but-pro range, and are made by Behringer, Allen & Heath, Soundcraft, PreSonus, Yamaha, Roland and others. Yamaha currently leads the way in innovative features (at a steep premium, and well beyond those listed here). DigiDesign and Midas are a couple other premium brands. Here are some key features that make digital consoles desirable.

Double as an Interface: Digital mixers have a standard computer bus (USB, Firewire, Thunderbolt) so they can act as multichannel DAW controllers/recorders. Increasingly, you can send every channel to the DAW individually.

Flying Faders and Scenes: A flying fader is a fader with a motor. Link faders together and they’ll all move when you move one. Save snapshots (scenes) of where everything on the mixer is located and you can recall it in an instant; this is especially helpful if nothing changes each night, or if artists are on a repeating rotation at a festival.

Scribble Strips: Each channel can be color-coded, and have it’s own text and/or image so you can throw out the masking tape and Sharpie.

Ultra-flexible: Besides usually having more aux outputs than analog consoles, digital consoles also have many mix groups, DCA groups, mute groups, solo groups, pages, sets, scenes, and sometimes a full routing matrix (introduced first by Dante). These all allow for much more flexible grouping and routing.

Fewer Pots that do More: There is one set of pots for common things like compression, gain, EQ, and sends. There are other pots, coupled with a digital display, for thousands of other options that simply can’t fit on an analog console. There are also often use-definable pots and buttons for quick access to anything.

Digital Snakes: Going along with digital mixers are digital snakes. An analog snake requires a separate set of conductors for every input. It ends up being a very heavy cable since it’s basically 8-32 XLR cables in one, fat snake. Then, there are XLR/TS connectors on each side for every channel, and they’re prone to breaking. A digital snake uses either a network or fiber optic cable for 8-32 channels of audio. It’s much easier to deal with on both ends and in the space between.

Resources for this Section

This book provides in-depth tips for live sound from both the engineer and performer’s perspective, making it very flexible for educational use.

Being the most popular console at the moment, here is the X32 resources playlist from Behringer’s channel.

Yamaha also has a series of live classes engineers often attend to be Yamaha cerfied.