“Lengthening” is a better vowel dimension than “rounding”

The impressionistic phonetic specification of vowel quality is usually given in terms of the quasi-articulatory dimensions "height," "backness" and "rounding," relative to the quality of the cardinal vowels placed in a stylized vowel quadrilateral. For some purposes, an acoustic approach to vowel dimensions may be preferable. A system of reference vowels created by a scaling discretisation of formant space (SDF) is used in this study to derive new acoustic dimensions closely aligned to the traditional dimensions mentioned above. Some implications of the new acoustic dimensions for vowel classification are investigated, using a well-known vowel dataset. Based on this analysis, it is argued that "lengthening" is a more appropriate vowel dimension than "rounding."