Optimizing a High-Order Graphic Equalizer for Audio Processing

A high-order graphic equalizer has the advantage that the gain in one band is highly independent of the gains in the adjacent bands. However, all practical filters have transition bands, which interact with the adjacent bands and create errors in the desired magnitude response. This letter proposes a filter optimization algorithm for a high-order graphic equalizer, which minimizes the errors in the transition bands by iteratively optimizing the orders of adjacent band filters. The optimization of the filter order affects the shape of the transition band, thus enabling the search for the optimum shape relative to the adjacent filter. The optimization is done offline, and during filtering only the gains of the band filters are altered. In an example case, the proposed method was able to meet the given peak-error limitations of ±2 dB, when the total order of the graphical equalizer was 328, whereas the non-optimized filter could not meet the requirements even when the total order was raised to 672. Optimized high-order graphical equalizers can be widely used in audio signal processing applications.