Simplified equivalent circuit of integrated op amp tone control circuit (a)

At high frequency, q and Cz can be regarded as short circuits (that is, RPi does not exist), as shown in Figure 4-6 (a), which can also be equivalent to Figure 4-6
(b). So there is:
    the maximum increase in high frequency: AVI≈(RI +R3 +2Rz)3; the
maximum attenuation in high frequency: ^ vc≈3/(Ri +R3+2Rz).
  In the above two equations, it is assumed: RP2》 (Rt October 3+2R2),
high frequency increase turning frequency:, III= l/?.7tR3 C2.
(Unit: f to ratio, R- fl (Europe), C- F (coward))