Signal Processors - Shure MUSIC EDUCATORS Manual

Signal Processors

A signal processor enhances the audio signal, or can assist in correcting
imperfections in the sound system. While not usually essential to the operation of a
sound system, they offer some significant advantages. Signal processing equipment
includes equalizers, special effects processors, and dynamic processors.
Equalizers come in two basic varieties: graphic and parametric. The graphic equalizer
(see figure 14) is the most common type. The controls on a graphic equalizer consist
of a row of faders that are used to cut or boost specific frequencies. The more faders
there are, the more precise the level of control. Each fader represents a "band";
common graphic equalizers are 5-band, 10-band, 15-band, and 31-band. Graphic
equalizers give the user visual "feedback" (no pun intended) by graphically representing
which frequencies have been cut or boosted. While easy to use, graphic equalizers
only allow alteration of the frequencies shown on the front panel. For example, a 31-
band equalizer allows you to cut at 400 Hz (Hertz) and 500 Hz, but not anywhere in
between. A cut at 450 Hz could be simulated by reducing both 400 and 500 Hz,
but this results in cutting more frequencies than is necessary. A parametric equalizer,
on the other hand, offers more precise control. Fully parametric equalizers consist of
three controls; frequency, boost/cut, and bandwidth. The frequency control permits
the user to select a specific frequency, the boost/cut control selects how much that
frequency is raised or lowered, and the bandwidth control selects how many adjacent
frequencies are affected by the adjustment.
Figure 14: Graphic Equalizer
Equalizers are often employed in an attempt to control feedback. While not the
ultimate solution (see sidebar on feedback), they can be a useful tool in this applica-
tion. To begin, turn on all microphones, and raise their individual levels to the point
where they will most likely be used during the performance. Slowly bring up the
master output level of the mixer until feedback occurs. Now go to the equalizer and
pull down the offending frequency roughly 3dB (decibel). If the feedback is a "hoot"
or "howl" try cutting in the 250 to 500 Hz range. A "singing" tone may be around 1 kHz.
"Whistles" and "screeches" tend to occur above 2 kHz. Very rarely does feedback
occur below 80 Hz or above 8 kHz. It takes practice to develop an ear for equalizing
a sound system, so be patient. After locating the first feedback frequency, begin
turning up the system again until the next frequency begins ringing. Repeat the above
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