Graphic Equalizer Design with Symmetric Biquad Filters

A novel graphic equalizer design comprised of a single second-order section per band is proposed, where the band filters have a symmetric shape about their center frequency in the entire audio range. The asymmetry of the band filters at high frequencies close to the Nyquist limit has been one source of inaccuracy in previous designs. The interaction between the different band filters is accounted for using the weighted least-squares design, which employs an interaction matrix. In contrast to prior works, the interaction matrix is designed with a different prototype gain for each band filter, helping to keep the maximum approximation error below 1 dB at the center frequencies and between them when the neighboring command gains are the same. An iteration step can further diminish the approximation error. Comparisons of the proposed design with previous methods show that it is the most accurate graphic equalizer design to date.