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Traditionally, the formant frequencies are regarded as the most important characteristics of the frequency spectra of vowels. It is possible, however, to approach the differences between vowel spectra in a more general way by means of a dimensional analysis. For a particular vowel, the sound-pressure levels in each of a number of frequency passbands can be considered as coordinates of a point in a multidimensional Euclidean space. Different vowel spectra will result in different points. Frequency spectra of 15 Dutch vowels were determined with 18 bandpass filters (10 speakers). The analysis indicated that the “cloud” of 150 points can be described by four independent dimensions that are linear combinations of the original 18. The percentage of total variance “explained” by these dimensions were 37.2%, 31.2%, 9.0%, and 6.7%, respectively. This approach presents interesting perspectives for the development of vowel-discrimination equipment.
Plomp et al. (1967) studied this question.