Audio Engineering

Recording Consoles 785

adjustment of bass and treble ranges, as illustrated in Figure 27.12. This type of response
(for fairly obvious reasons) is often termed a “ shelving ” equalizer. So, the Baxandall
shelving EQ is invariably appended with a midfrequency equalizer, which is tunable
over a range of frequencies, thereby enabling the sound engineer to adjust the middle
band of frequencies in relation to the whole spectrum (see also Figure 27.12 ). A signal
manipulation of this sort requires a tuned circuit, which is combined within an amplifi er
stage, which may be adjusted over a very wide range of attenuation and gain (perhaps as
much as 20 dB). How such a circuit is derived is illustrated in Figure 27.18.

Figure 27.18(a–c) : Derivation of midband parametric EQ circuit; see text.

In

VRI A

B





Out

Z 1

(a)

In

VRI





Out

(b)

(c)

P 



Rb

Ca

Ra

P

Rb Ra

L Ca