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