Spectral analysis of sung vowels. I. Variation due to differences between vowels, singers, and modes of singing.

Average 1/3-oct filter spectra of vowels, sung by seven professional male and seven professional female singers , were measured. The material consisted of nine different vowels, sung at six fundamental frequencies (F0, ranging from 98 up to 880 Hz). For each vowel the singers were requested to sing in the following nine modes: neutral, light, dark, pressed, free, loud, soft, straight, and extra vibrato . To study origins of spectral variation, the quantity of spectral variance, based on band filter sound levels, was used. For each fundamental frequency and separately for males and females, portions of total spectral variance associated with the main effects and the interactions of the factors "vowels," " singers ," and "modes of singing," were computed. A considerable decrease in total spectral variance was found when F0 rose from 98 to 880 Hz, mostly due to the reduced spectral variance between vowels. Above about F0 = 660 Hz spectral variation was dominated by differences related to singers and modes of singing. Additional analyses revealed that for all F0 values vowel spectra of the tenor and the soprano singers varied more than those of the bass and the alto singers , there was only a slight dependence of spectral differences between vowels on the mode of singing, and the amount of spectral variation in a vowel, sung by different singers with different modes of singing, was vowel dependent.