The warping filters where introduced years ago for loudspeaker equalization in order to solve the lack of resolution of the linear filters at low frequencies, and also to follow the frequency resolution of psycho-acoustic scales like the Bark scale, with a more logarithmic than linear behavior. However, this improvement in the frequency resolution at low and mid frequencies is done at the expense of loosing resolution at high frequencies and increasing the complexity of the filter and its implementation computational cost. In this paper a smart combination of linear and warped filter structures previously developed by the authors for FIR filters is presented with new contributions and extended to IIR filters. This combination saves computational cost and obtains a proper frequency resolution at the whole frequency band, obtaining better results for the same computational cost that when using linear or warped filters alone. The results have been subjectively tested using the ABX methodology with successfully results. The presented filter structures, methodology, and apparatus to do the filtering are patent pending.
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