Preamplifi ers and Input Signals 231By this means it is possible, by combining elements of frequency lift or cut, to choose
from a variety of possible frequency response curves without losing the ability to attain a
linear frequency response.
7.18.2.4 Parametric Controls
This type of tone control, whose frequency response is shown in Figure 7.55 , has
elements of similarity to both the standard bass/treble lift/cut systems and the graphic
equalizer arrangement in that while there is a choice of lift or cut in the frequency
response, the actual frequency at which this occurs may be adjusted, up or down, in order
to attain an optimal system frequency response.
A typical circuit layout is shown in Figure 7.67.
7.18.2.5 The Graphic Equalizer System
The aim of this type of arrangement is to compensate fully for the inevitable peaks and
troughs in the frequency response of the audio system, including those due to defi ciencies
in the loudspeakers or the listening room acoustics, by permitting the individual
adjustment of the channel gain, within any one of a group of eight single-octave segments
of the frequency band, typically covering the range from 80 Hz to 20 kHz, although 10
octave equalizers covering the whole audio range from 20 Hz to 20 kHz have been offered.
Ein0.1μ 82 K 22 K 12 K 15 K 27 K 100 K 0.068μ2M20V0V91 K
Flat39 K0.0039μ
0V0.068μ0.022μEoutFigure 7.65 : The Quad tilt control.