Audio Engineering

228 Chapter 7

7.18.2.2 Slope Controls

This is the type of tone control employed by Quad in its type 44 preamplifi er and operates
by altering the relative balance of the LF and HF components of the audio signal, with
reference to some specifi ed midpoint frequency, as is shown in Figure 7.53. A typical
circuit for this type of design is shown in Figure 7.65.

The philosophical justifi cation for this approach is that it is unusual for any commercially
produced program material to be signifi cantly in error in its overall frequency

f 1  2 πR^1

2 C 1

f 2  2 πR^1

1 C 1

Frequency

Output (dB)

3dB

3dB

R 1

C 1

R 2

0V

Ein Eout

Figure 7.62 : A modifi ed treble-cut (low-pass) RC circuit.

R 2

R 1

3dB

Output (dB)

Frequency

f 1 ^1

3dB

0V

C 1

Ein Eout

2 πR 2 C 1 f^2 

1

2 πR 1 C 1

Figure 7.61 : Modifi ed bass-cut (high-pass) RC circuit.