The EM Poll

P.A. 101

Mar 14, 2008 3:24 PM, By Emile Menasche

           

HOW TO CHOOSE THE RIGHT SOUND SYSTEM FOR YOUR NEEDS WITHOUT TEARS

A Typical Mixer Channel

Before choosing a mixer, take a look at this breakdown of a typical mixer channel. Not all mixers offer every feature listed here, but you might not need all of these features.

Direct output. A direct feed from the channel, these outputs are commonly used to feed a recording mixer.Insert point. Inserts are send-and-return jacks used to feed outboard effects such as compressors, gates, and EQs. Some mixers use separate 11/44-inch jacks for the send and the return. Other boards employ one 11/44-inch TRS (tip-ring-sleeve) jack for both send and return circuits.

Line input. Balanced or unbalanced 11/44-inch line inputs are commonly used for line-level gear such as keyboards, preamps, effects, and some outboard submixers.

Mic input. Typically, you use an XLR input for connecting microphones and balanced signals from a direct box. (A direct-injection box, or DI, is useful for plugging in instrument-level signals such as those from guitar and bass.) However, some low-end mixers may offer 11/44-inch TRS mic jacks for use with high-impedance dynamic mics.

Gain (or trim) pot. This potentiometer (basically a variable resistor) attenuates the input level. For the best sound, you usually should set the gain to the highest setting that doesn't produce distortion. Adjusting the gain pot is a part of setting all of the signal levels throughout the system, so that the system as a whole delivers the maximum amount of undistorted sound while allowing headroom for the engineer to make adjustments during the show. Creating this balance is called gain structuring.

Line/mic switch. This useful feature allows you to match the operating level of your input to the output of your gear. In some mixers, the switch routes the input signal to the channel mic preamp for use with mic-level signals or circumvents the mic preamp for use with line-level signals.

Equalizer. The typical 3-band EQ offers high and low shelving bands (each with fixed cutoff frequencies). The midrange band usually is semiparametric, which means it lets you set the level and "sweep" the center frequency, altering which frequencies are affected. Some boards offer fully parametric EQ, which also offers control of the bandwidth or Q. However, some mixers have more elaborate channel EQ. The most common variety is a 4-band EQ that has high and low shelving bands and two semiparametric or parametric midrange bands.

Low-cut switch. This low-frequency rolloff is especially useful for eliminating the stage rumble that transmits up a mic stand and through the system.

Auxiliary sends/monitor sends. Aux sends typically feed effects processors, whereas monitor sends, as you would guess, carry monitor mixes.

Many consoles allow you to set the sends as either prefader or postfader, using a front-panel switch or an internal jumper. Typically, an effects processor should be connected to a postfader send so that the position of the channel fader affects the send. (As the name implies, a postfader send splits off of the signal path after the channel fader.) This send can be used to add reverb, delay, and other sweetening to the mix. Some boards have buses labeled "effects send"; in most cases, these are simply postfader aux sends, but with mixers that have built-in effects, the effects send is usually hardwired to the internal effects processor.

Since a prefader send splits off before the channel fader, its level is not affected by the fader. That is desirable for monitors because the engineer can adjust the house mix during the show without changing the monitor mix.

Bus assign. If your mixer offers submix buses (often called subgroups), you use the bus assign buttons to route channels to subgroups. You can use the submix bus to group multiple channels (such as a drum, background vocal, or keyboard mix) so that the entire submix can be controlled with a single fader. Subgroups also are handy for creating a separate mix that feeds a 2-track recorder.

Pan. As with home stereo gear, the pan pot sets the stereo position of the channel. Some mixers offer stereo pairs of channels (for example, channels 17/18) with line inputs; in this case, the pan control sets the balance between the odd- and even-numbered channels.

Fader. This sets the output level feeding the master and submix buses.