A comparison of vowel normalization procedures for language variation research

TLDR

The study evaluates vowel normalization procedures to facilitate research on language variation. The authors compared multiple vowel normalization methods on recordings from 160 Dutch speakers, assessing their ability to preserve phonemic and sociolinguistic information while reducing anatomical variation using statistical pattern analysis of F0 and formant measurements. Normalization methods that use information across multiple vowels outperform those relying only on the vowel itself, and individual formant normalization yields better results than formant‑extrinsic approaches.

Abstract

An evaluation of vowel normalization procedures for the purpose of studying language variation is presented. The procedures were compared on how effectively they (a) preserve phonemic information, (b) preserve information about the talker’s regional background (or sociolinguistic information), and (c) minimize anatomical/physiological variation in acoustic representations of vowels. Recordings were made for 80 female talkers and 80 male talkers of Dutch. These talkers were stratified according to their gender and regional background. The normalization procedures were applied to measurements of the fundamental frequency and the first three formant frequencies for a large set of vowel tokens. The normalization procedures were evaluated through statistical pattern analysis. The results show that normalization procedures that use information across multiple vowels (“vowel-extrinsic” information) to normalize a single vowel token performed better than those that include only information contained in the vowel token itself (“vowel-intrinsic” information). Furthermore, the results show that normalization procedures that operate on individual formants performed better than those that use information across multiple formants (e.g., “formant-extrinsic” F2-F1).