An investigation into vocal tract length normalisation

This paper investigates several di erent methods for performing vocal tract length normalisation (VTLN) which are either completely linear or piece-wise linear. Furthermore the combination of VTLN with either standard unconstrained maximum likelihood linear regression (MLLR) or constrained MLLR is considered. Results on the Switchboard corpus show that there is little di erence in performance between the di erent forms of VTLN, and that as previously reported that the e ects of VTLN and unconstrained MLLR are largely additive. However it was found that if multiple iterations of constrained MLLR is used there is no additional advantage to also using VTLN.