Spectrographic Determination of Vowel Quality
Peter Ladefoged · The Journal of the Acoustical Society of America · 1960
Thirty-one sets of eight equivalent vowels were analyzed on a modified Kay Sona-Graph. The formant frequencies of vowels such as [e, ɛ, a]) usually could be determined unambiguously by visual inspection and measurement of the spectrographic displays. But the spectrograms of [i, ɑ, ɔ, o, u] often provided inadequate data for determining the precise formant frequencies. The analysis indicated that it is generally true that the quality of a vowel can be specified in terms of the relationship between the pitches of its first three formants and the pitches of the first three formants of other vowels spoken by the same speaker. But in very high vowels, like [i, u] where it is difficult to determine the formant frequencies (and hence the pitches) from spectrographic data, the quality may be specified in terms of other auditory attributes such as the pitch of formant two and the relative loudness of formants two and three (the precise pitch of formant one being of less relevance). For very back vowels like [ɑ ɔ, o, u] the chief auditory quality may be the mean pitch of formants one and two and the comparative absence of energy in the upper part of the spectrum.