Cancelling gain from a filter
The article linked in the question states (page 67): -


  The Q-factor and the resonant frequency are not independent in this
  circuit. For high frequencies, the bandwidth will be the same as that
  for low frequencies. This, in general, is not a desirable feature. For
  example, in an audio mixing desk, the equalising section would use a
  state-variable circuit where the bandwidth changes with the higher
  frequencies.


It's all there in black and white - research the state variable filter and use that instead.