FREQUENCY WARPING USING ALL-PASS TRANSFORMATIONS
Recall the bilinear transform:
which implements a nonlinear warping of the frequency axis:
This can be implemented as a series of all-pass transformations:
The cepstral coefficients are input and the output are frequency-warped
cepstral coefficients. This is an interesting way to implement
speaker-specific warpings (e.g., male vs. female speakers).