Audio Mixers Buyer's Guide: Mix it Up (page 2)

If you are setting mic and amp inputs for stereo playback of audio for video, it's important to keep screen position matched with the audio image. You don't want your far left lead guitar player wailing from the right speaker. It's easy to keep straight. Channel 1 takes the left signal, 2 the right. All the audio channels follow in kind, odd to left, even to right. You can also use the mixer's pan pots to assign them to left and right. In post, a pan pot is a great way to accentuate sound moving across the screen, such as an ambulance dashing to the hospital.

Auxiliary Send is the next step. This enables you to route the signal to an outboard processor such as reverb, limiter, or to remove the "S", or sibilance, on voice-overs. One advantage of using one of these hardware devices compared to software processing in post is that you can hear the results live. Some mixers have pre and post switches so you can monitor the bus before or after the processing. Other mixers have effects built in.

Equalization, known as EQ, is frequency control. Some mixers employ a simple low cut filter where the bass frequencies are attenuated, useful if you want to eliminate stage noise from a vocal mic. Some use high cut, which will attenuate hiss. The simplest form of equalization is graphic, dividing the audio spectrum of 20Hz to 20kHz into multiple slices which you boost or cut according to your preference. A glance at this device gives you a graphic representation of your frequency modification.

Most audio mixers used in video settings break the signal into bass, midrange and treble with knobs that allows you to attenuate or accentuate each. Better mixers split the frequencies into more bands. Parametric equalization is more sophisticated, a three-stage process. First you isolate the frequency you need, then you boost or cut it, and finally you determine the bandwidth of your adjustment.

The solo switch allows you to isolate each channel for monitoring. Some mixers also have mute buttons to kill a channel. Another common switch is cue, which allows you to select any audio input signal to monitor through the headphone jack without affecting master output.

Each channel finishes with a fader, either a rotary knob or slider. Sliders are easier to use and give you a quick visual reference as to which channels are in use and what their relative volumes are. Knobs are more common on compact mixers where available space is at a premium.

Once you've assigned the channel's signal to one of the two output channels, master faders monitored by a VU meter will control the overall volume. Your output audio should have an average peak at 0dB. It is okay for transients to slide into the red zone, but the needle should not peg (overdriving the meter). On digital meters, you should shoot for a level where the signal consistently peaks on the last green LED, occasionally dipping into the yellow, but never hitting red, which signifies signal overload.

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