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User Manual
4. Applications & Techniques (contd.)
© LA Audio 2004
16
Another useful effect that can be created with a graphic EQ is a ‘Comb Over’. To give
a mono source some interest in a stereo mix, the graphic equaliser can be used to
create variances in each side of the stereo signal, thereby widening the sound. Route
the mono signal to both channels of the EQ231G-SP and on each channel cut
alternate frequencies by around 6dB. With certain source material, you may need to
cut less at low frequencies to avoid an imbalance in the stereo image.
f) Reduction of feedback
In many auditoriums, a graphic equaliser may be used to increase the gain before
feedback (GBF). Essentially, this involves cutting the frequencies associated with
feedback to allow the system to be safely turned up.
The usual method is to set the graphic equaliser to a "flat" position, (i.e. all sliders at
0dB) and to increase the overall level in the auditorium, until feedback commences.
Then reducing the level to just under the feedback point, each frequency band in turn
is boosted until the feedback frequencies have been identified. Some practice will
enable you to identify frequencies by ear to speed this adjustment. By notching the
offending bands down slightly, the overall level may be increased. This may be
repeated until the overall gain reaches the required level.
It is worthwhile to note that if boosted sufficiently, all frequencies will eventually feed
back, so a balance should be struck between gain and tonal integrity, as extreme EQ
adjustments can have a detrimental effect on audio quality. Moreover, the graphic
equaliser is not the only tool at an engineer’s disposal for improving GBF: good
microphone and speaker placement will often reduce the severity of EQ required to
achieve sufficient gain.
g) Graphic equalisers and dynamics
In most instances, it is good practice to place graphic equalisers before any dynamics
processors such as compressors or limiters. This is for two main reasons:
As the graphic equaliser is essentially a set of volume controls (albeit frequency
specific ones) and dynamics units respond to volume, it is best to cut or boost
frequencies as desired before applying compression. This ensures that the
compressor or limiter only acts on frequencies that will be present at the output. This is
particularly important with low frequencies, which are more likely to trigger the