High-Order Digital Parametric Equalizer Design

A family of digital parametric audio equalizers based on high-order Butterworth, Chebyshev, and elliptic analog prototype filters is derived that generalizes the conventional biquadratic designs and provides flatter passbands and sharper bandedges. The equalizer filter coefficients are computable in terms of the center frequency, peak gain, bandwidth, and bandwidth gain. We consider the issues of filter order and bandwidth selection, and discuss frequency-shifted transposed, normalized-lattice, and minimum roundoff-noise state-space realization structures. The design equations apply equally well to lowpass and highpass shelving filters, and to ordinary bandpass and bandstop filters.