Desain, P. (1999) Vibrato and portamento, hypotheses and tests. Acustica 348. ISSN: 1436-7947.

Abstract As Seashore already pointed out, continuous aspects in music performance, which happen during and in-between notes, can be a relevant means for expression. These modulations, like vibrato and portamento, are very consistently controlled and seem to exhibit striking regularities. However, there are many conflicting hypotheses in the literature about these regularities, especially concerning the relation between vibrato and global tempo. To investigate these more systematically, experiments were conducted in which different instruments perform the same piece at different tempi. The results, relating vibrato rate, extent and phase to tempo and timing will be presented. Apart from understanding the process of music performance better, they may be applied in the design of synthesizers and software for the music studio.

More on continuous modulations