A comparison of three speaker-intrinsic vowel formant frequency normalization algorithms for sociophonetics

This article evaluates a speaker-intrinsic vowel formant frequency normalization algorithm initially proposed in Watt & Fabricius (2002). We compare how well this routine, known as the S-centroid procedure, performs as a sociophonetic research tool in three ways: reducing variance in area ratios of vowel spaces (by attempting to equalize vowel space areas); improving overlap of vowel polygons; and reproducing relative positions of vowel means within the vowel space, compared with formant data in raw Hertz. The study uses existing data sets of vowel formant data from two varieties of English, Received Pronunciation and Aberdeen English (northeast Scotland). We conclude that, for the data examined here, the S-centroid W&F procedure performs at least as well as the two speaker-intrinsic, vowel-extrinsic, formant-intrinsic normalization methods rated as best performing by Adank (2003): Lobanov's (1971) z-score procedure and Nearey's (1978) individual log-mean procedure (CLIHi4 in Adank [2003], CLIHi2 as tested here), and in some test cases better than the latter.