Acoustic details of vibrato cycle in tenor high notes

It is generally assumed that modulation of intensity within the vibrato cycle is at least partially due to the varying proximity of voice source partials to vocal tract formants. However, accurate measurements of this effect are difficult to obtain, since it occurs in a context of other time-varying factors that can also affect sound pressure level (SPL). In this experiment, the varying frequencies and levels of the partials, as they move toward and away from F1, F2, and the "singer's formant," respectively, are displayed in three-dimensional power spectra (including the time dimension). The components of the SPL are analyzed by a computer program, documenting the shifting prominence of the various partials and formants as fundamental frequency (F0) modulates. Consideration is given to the role of vibrato in facilitating the singer's task of tuning the vocal tract for optimal resonance. The subject is a professional operatic tenor of robust voice.