A parametric approach to vocal tract length normalization

Differences in vocal tract size among individual speakers contribute to the variability of speech waveforms. The first-order effect of a difference in vocal tract length is a scaling of the frequency axis; a female speaker, for example, exhibits formants roughly 20% higher than the formants of from a male speaker, with the differences most severe in open vocal tract configurations. We describe a parametric method of normalisation which counteracts the effect of varied vocal tract length. The method is shown to be effective across a wide range of recognition systems and paradigms, but is particularly helpful in the case of a small amount of training data.