The Mixer

The first time I stepped into a pro studio and saw a mixing console the size of a dining table, its top studded with hundreds of knobs and blinky lights, I was awestruck and intimidated. But in truth, a mixer is a fairly simple device. A mixer doesn’t make any sound on its own — all it does, basically, is route audio signals from one place to another.

Mixers aren’t just for big studios. Once your home studio grows to include more than one or two devices that make sound but have no speakers of their own, you’ll need a mixer. If your band plays live shows with more than one microphone, again, a mixer becomes a necessity.

Fortunately, mixers are available to suit any budget and any combination of needs. In this column I’ll explain what mixers do and point out some key features to look for.

In a home studio, most people plug the audio signals from several sources into a mixer. The sources may include their computer, a keyboard, and perhaps a second keyboard, a rackmount synth module, or a vintage drum machine. The mixer needs to have enough inputs to accommodate all of the signals. The main stereo output of the mixer is then attached to the studio monitoring system, which could be a pair of powered monitors or a stereo amplifier that drives the monitors.

Mixers perform five or six basic tasks:

• Combining two or more audio inputs into a single audio output. (That’s the “mixing” part.)

• Controlling the level (loudness) of each signal at each point along the signal path.

• Panning each signal to the left or right in the stereo field.

• Changing the tone of signals using equalization (EQ).

• Routing the incoming audio signals to one output or another. For example, a stage mixer might have one output to feed the main house P.A. system and a separate output to feed onstage monitor speakers. After turning down the main house feed, you can play your instrument to check the sound and not be heard by the audience.

• Providing meters (often called VU meters) with which you can check the loudness of a signal visually.

The controls of most mixers are laid out in vertical columns called channel strips (see Figure 1). Each channel strip houses the controls for one input channel. To the right side of the mixer is a separate section called the master section, which contains output level controls and a few other things.

To use a mixer, you plug each signal source into one of the rear-panel jacks (or into two adjacent jacks if the source has stereo outputs). Bring up the master output level, and then use the vertically mounted sliders — they’re most often called faders — to adjust the relative levels of the signals while playing your music.

If you can’t get one of the signals loud enough, or if one is so loud that it distorts, you’ll need to adjust the input trimpots (see Figure 2). These are usually found at the upper end of the channel strip.

Perhaps the most important thing to watch for when buying a mixer is to make sure that it has the type(s) of inputs you need. To make connections with the rest of your gear, you need to consider both the type of physical connector and the signal level. Just because you see the right type of connector (¼" phone jack, RCA phono jack, three-pin XLR connector, etc.) there’s no guarantee the mixer will be able to handle the signal level(s) coming from your other gear.

The outputs of most studio gear, including your keyboard and computer, are at line level. Without getting into technical detail, it’ll suffice to say that most mixers, except some that are designed specifically for P.A. use, have line-level inputs.

P.A. mixers have inputs for microphones. The signal coming from mics, electric guitars, and turntables is typically at a much lower level than line level. Your mixer will need mic-level and/or instrument-level inputs in order to accept the signal from a mic or guitar. (Many mixers have both mic- and line-level inputs.) If you plug a low-level signal into a line-level input and attempt to crank it up loud enough to hear, you’ll add all sorts of background noise.

Some mic cables have three-pin XLR connectors. However, not all of the XLR inputs on a mixer are suitable for mics. Some are a type of line-level input called a balanced connection. For further details on audio signal levels and types, you might want to consult the short but decent tutorial at Transom.org (www.transom.org/tools/basics/200207.analogbasics.html).

When buying a mixer, tell the salesperson what equipment you’re planning to connect to it. The salesperson will be able to help you figure out what features you need.