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In live sound applications, graphic equalisation is almost always applied separately to the stage monitor of
foldback system to reduce the level of those frequencies that would otherwise cause feedback problems. These
problems came about due to peaks in the frequency response curves of the monitor speaker systems, monitor
positioning, and sound reflected from the stage walls. An analyser is probably best employed to do this
effectively but many experienced engineers rely on their ears.
In addition to compensating for room acoustics, equalisation can also be used to counteract some of the
problems caused by microphone characteristics and positioning or to tailor the response to improve speech
intelligibility. Also, many speaker systems have a far from flat response, particularly mobile systems that
have to be positioned in physically convenient places rather than the acoustically ideal ones. When equalising
the room, these deficiencies are also catered for to a large extent.
Whatever the application, it is generally better to try to attenuate peaks rather than to attempt to boost the
surrounding frequencies to the same level, Furthermore, all peaks can be reduced be attenuating their respective
band but some response dips simply cannot be corrected. An example is crossover cancellation where very
deep notches may appear covering two or three bands. Attempting to level the response by excessive boosting
will simply eat up system power and achieve no useful result. Ultimately a dip in the response is not so audibly
objectionable as a peak and so it may be as well to leave these dips alone or to try and solve the problem at
source by checking your crossover systems and horn alignment.
In broadcast studios, graphic equalisers are often used during phone-in shows to help compensate for the
restricted bandwidth of telephone lines. No equaliser can completely correct the signal in this way as it is
impossible to boost frequencies that don't exist and telephone lines have a very restricted bandwidth.
Nevertheless, the improvement in subjective terms can be dramatic.
Creative uses may include studio work, live or recorded drama and film soundtrack recordings. Voices may
be harshly filtered to simulate telephone conversation or the tonal characteristics of an instrument may be
modified to fit in with a particular mix.
Though other types of equaliser can often to this job, the graphic equaliser is still the easiest to set up and the
controls give an instant visual presentation of the response curve. In the commercial studio where time is often
of the essence, this attribute should not be overlooked.
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