FFT with modified frequency scale for audio signal analysis

Frequency axes of acoustic spectra are conventionally expressed on a logarithmic frequency scale. In this paper, a new procedure for frequency analysis of audio signals is presented. The linear frequency scale of the FFT is mapped into nearly logarithmic one using second-order allpass filter. Unlike first order allpass filters, which are unable to adequately approximate logarithmic scale, the ambiguity of frequency mapping must be considered when higher order allpass filters are used in warping procedure. We have achieved one-to-one frequency mapping in case of the second order allpass frequency warping by utilizing of complex, analytic signal.