Implementation of frequency-warped recursive filters

Frequency-warped "lters are bene"cial in many audio applications because they inherently use nonuniform frequency resolution which may be matched so that it approximates the frequency representation of hearing. Warped transversal "lters are immediately obtained by replacing the unit delays of a conventional "lter with "rst-order allpass blocks. Implementation of warped recursive "lters is a problem since those "lters contain delay-free loops. A technique to implement any such "lter without changing the coe$cients or the structure of the "lter is presented in this paper. In addition, a method to modify such a "lter to a new structure where the delay-free loops are eliminated is introduced. 2000 Elsevier Science B.V. All rights reserved.