Audio Mixers Buyer's Guide

With the video world inundated in software solutions that promise the liberation from all things analog, is there a place for the traditional audio mixer in your edit suite or production toy box? Looking at this line up of affordable mixers for studio and field, the answer is a definite yes.

Virtual mixers are present in most video editing software and they can create some quality results in customizing the audio portion of your program, such as creating the proper balance between tracks or mitigating noise with sophisticated filters. However, when your program leaves the safe haven of the computer for a variety of analog destinations, or when you need to acquire audio from a variety of analog sources, there is no better friend than your audio mixer.

Many video folk have a love-hate relationship with audio and have always felt the mixer was somewhat of an un-favored stepchild in their family of gear. The mixer often took up too much room, was confusing in its design, had too much of what they didn't need and not enough of what they did and, to top it all off, they cost too much. Well, that was then. Audio mixers are now smaller, lighter, electronically quiet and affordably priced.

The most difficult task for the video-centric hobbyist is assessing the I/O needs for studio or field production and understanding the capabilities and, in some cases, the limitations of, an audio mixer for those applications.

Anatomy of a Mixer
Mixers can be a bit confusing at first glance, with the scores of knobs buttons and sliders that cover the interface. However, if you look at one channel column at a time, you'll notice a remarkable amount of redundancy repeated in the adjacent channels. The key phrase is "know one channel, know them all."

Looking at the first channel of a mixer, we can follow the path of the audio signal beginning with the inputs and ending at the fader.

Inputs There can be a number of ways to get audio into your mixer. One microphone-level balanced XLR and one balanced/unbalanced 1/4-inch phone plug line level input are typical. The XLR accepts a low-level microphone input only, and the mixer can often supply +48v DC Phantom power to that type of input alone. The 1/4-inch input will take a balanced or unbalanced line level depending on the type of plug inserted. Make sure you understand the complexity of your sources and match that to your mixer needs. For example, a 1/4-inch balanced professional input has a +4db level that is too hot for unbalanced consumer line level (-10db). This kind of information is also important when going out from the mixer.

Low Cut Filter The low cut takes all audio below 75-80Hz and drops it to nothing. This is invaluable for getting rid of wind noise and the low rumble of machinery and is a critical feature on a field mixer.

Trim The trim is a sensitivity adjustment for the selected input and it works in tandem with the channel fader (slider) to create the most neglected technique in audio: gain structure. Proper gain structure insures that the signal running through the mixer is strong, and above the noise floor of the electronics, without being pushed to distortion. Faders should be positioned at the unity gain level (and not at the bottom) and the sensitivity of the incoming signal should be trimmed in relation to the fader at unity. This is gain structure. This gives the fader a longer throw to change the level of the signal than when it is at the bottom of its scale.

Aux Sends Auxiliary sends are rotary potentiometers (pots) that tap into the signal in the channel after the input, sending the signal to auxiliary destinations. So, even though the mixer has two main stereo outputs, there is potential for many more combinations. Aux sends can feed decks, headphones or sound cards in whatever combination you need.

EQ The equalizing filters in software may be the ones you turn to for tweaking your audio, but with a worthy EQ section in the channel path of your mixer, you can save some serious time. Look for a mixer with high, mid and low bands, perhaps with a sweepable mid range. Sweeping the mid will allow you to find the offending frequency. EQ is one of the top ten tools in audio.

Pan The pan knob lets you place the audio signal to the right, left, center or anywhere in between in the stereo field.

Mute The mute button simply turns off the output on a channel. More professional mixers will route a muted signal to a different output for continued monitoring while the main output is muted.

Solo The solo button helps you isolate audio sources making it easier to track down and identify particular sounds or electronic noise.

Channel Fader Faders are sliders or rotary knobs that control the gain (volume) of a channel. They are the primary tools you'll use to perfect your mix.

Outputs The outputs from the mixer also need to match your destination device, whether this is a camcorder, DAT or your computer. Besides just matching the proper physical connection (e.g. XLR to 1/4-inch to RCA to 1/8-inch stereo mini), you also need to match the level of the output. Another important consideration might be a headphone jack so you can cue and monitor sources that are not going to the main output yet.

Home Suite Home
For post-production use on a mixer designed to stay connected in a permanent location, mixer manufacturers provide an adequate variety of input and output options. Most mixers have more line inputs than microphone inputs, so tallying up your line ins and outs and microphone requirements will quickly let you know if a particular model will meet your needs in this respect. Don't forget to include Aux sends as output sources; anyplace you can tap the signal is viable.

Take The Field
Field production mixers have a more limited and specialized use. These mixers are primarily made for powering up (phantom power), monitoring, amplifying and ultimately summing (adding together) multiple microphones and sending them to a single recorder. They are small, easy to operate from a field case, rugged and should ideally be able to run on battery power. All of these factors add up to a unit that does not cross over well into a studio setting and can be surprisingly expensive. Since most of these mixers come from professional climates, the I/Os are often centered around balanced audio connections, found on only a very small minority of camcorders.

A good field mixer that can take years of hard wear and tear and never let you down is worth its weight. Features to look for besides the number of microphone inputs and outputs are:

Phantom power (if your microphones require it)

Headphone monitor with separate gain control

VU meters

1kHz reference signal

Battery power

Low cut filters for each microphone

One thing is certain: whether you purchase a mixer for the edit suite, the field or both, your production and workflow will instantly improve. The difference in the finished product will not be subtle and, whether they know the reason why or not, your clients will notice the change.

[Sidebar: Follow the Path]
The simple definition of the audio mixer's job is the routing of audio signals from one place to another, the adjustment of intensity (amplitude) and frequency content (equalization) of those signals without adding an excessive amount of noise while passing through those electronics.

Bruce Coykendall | February 2003

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Audio Mixers Buyer's Guide

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