For years it was recognized that if
one could sweep the center or knee frequency
of an equalizer, this would
provide much more precise control of
the sound. The technique was very
costly due to the nature of the electronic
circuitry in early equalizers. The
coils (inductors) were either fixed in
value or very difficult to alter. Newer
circuits utilize relatively less costly
integrated circuit operational amplifiers,
plus relatively inexpensive capacitors
and resistors, to emulate the
function of the inductor, with the
added advantage of easily changed
circuit values. This has made it practical
to build stable, cost effective equalizers
with sweepable frequency controls.
The sweep type equalizer is much
like the multi frequency conventional
EQ discussed in Section 14.1.3, except
that instead of switching the center or
knee frequency, one can continuously
adjust it. One such sweepable equalizer
is illustrated in Figure 14-5