Cubic spline approximation of bilinear frequency unwarping

Nonlinear frequency warping is of recent interest in speech processing studies as due to its ability to extract speaker specific features. In particular, all pass Bilinear Transformation (BLT) is highly recommended tool in realizing such desired frequency-warping. Proposed work suggests a generic approach to unwarp formerly unmanageable second order BLT frequency mappings. Various spline approximation techniques have been analyzed to fit the inverse warping functions. Experiments have been performed to inverts first and second order warping approximations of state of the art Mel scale and bark scale. This method has been employed to derive inverse triangular filter bank for arbitrary frequency warping.