Specifications

AUTOMATIC MIXERS

Problems often arise when multiple microphones are used for recording or

sound reinforcement. As more microphones are added, pickup of reverberation

and unwanted room noise increases, which decreases intelligibility. In situations

where a sound reinforcement system is being used, additional microphones also

increase the likelihood of feedback or “howling”. These problems cause listener

fatigue, as it becomes necessary to concentrate harder to comprehend the

talker’s message. The solution is to activate microphones only when they are

being addressed and to keep them turned down when they are not needed. In

addition, when more than one microphone is addressed at a time, the overall

sound system volume must be reduced slightly to prevent feedback.

Automatic or voice-activated mixers are designed to do both of these things,

without the aid of a live operator. Automatic mixers

have special circuitry added

which senses when sound is arriving at a microphone, and then turns on that

microphone. The best units are able to turn on or “gate” the microphone in just

a few thousandths of a second - so fast that not even the first syllable is missed.

Some automatic mixers use ordinary microphones, while other types require

special microphones. The latter type can actually sense the location of the sound

source and activate the microphone only when the sound comes from the

desired direction. This prevents background noises, such as doors opening,

from fooling the mixer, no matter how loud they are.

SETTING AND ADJUSTING LEVELS

To achieve professional sounding results, it is important that the mixer you

use is equipped with a meter. Without one, it is nearly impossible to adjust

signal levels properly. The most popular type is called a VU meter

(VU

stands for “volume units”), and may be in the form of either a needle-type

indicator or a series of light-emitting diodes (LED’s).

During setup, first set the master gain control knob to about 3 or 4. Then

have each speaker talk into his or her microphone in a normal voice. Don’t

let them lean close to the microphone and quietly say “hello” - have them

state their name and enough other miscellaneous information (hometown,

etc.) to give you enough time to set an accurate level. Watch the meter

carefully, and adjust the input channel knob (also called a “fader” or “pot”)

so that the needle hovers below 0 VU, and only occasionally goes into the red

zone. If the meter is ever “pegged” (with the needle hitting the far end of the

scale), it means you’ve set that input level too high. Repeat this procedure

for each input channel. If you will be turning down mics that are not being

addressed, write down the appropriate setting for each channel on a piece of

tape and stick it on top of or in front of the mixer; this will make it easier to

set the right level quickly when someone begins talking. As the event begins,

watch your levels carefully; people often speak significantly louder when they

are live. For more dynamic talkers, you may have to turn their average level

down quite low in order to accommodate the occasional loud outburst.