Frequency warping with arbitrary allpass maps

A method for the computation of spectra with nonuniform resolution using a preprocessed fast Fourier transform (FFT), due to Oppenheim et al. (1971), is reviewed and extended to arbitrary allpass distortion maps. The magnitude response and distortion properties of the resulting infinite impulse response (IIR) cascade are no longer coupled; the resulting choices for frequency response compensation, including losslessness and power conservation, are discussed. The complexity overhead due to preprocessing is essentially linear in the number of fast Fourier transform (FFT) channels.