Ideally, the tone in messa di voce should remain constant and full in both piano and forte, as well as during crescendo and decrescendo. The vibrato rate, intonation and resonance should also remain as close to constant as possible. During messa di voce, breath support must be adjusted to the change in intensity in order to produce a constant pitch and compensate for natural tendencies such as straining and pushing. In other words, the singer must not go sharp during the crescendo and flat during the decrescendo.

Western operatic singers normally perform messa di voce using one of two different vocal techniques. In the first approach, the vocal folds are brought to their optimum state and are kept there for the entire exercise. The sound quality remains constant throughout the phonation without breathy initiation. The second technique involves a breathy beginning followed by a gradual closing of the vocal folds during crescendo and a gradual opening of the folds during decrescendo. The breathy sound eventually attains full timbre.

In the laboratory, among beginners and experienced singers, we found that few could control pitch and loudness independently. All singers encountered difficulties in maintaining resonance as well as consistency of vibrato with decrescendo; the decrescendo generally caused the most problems. The second technique lacks power and projection at piano as verified by weak spectral resonance, especially in the range of the singer’s formant.

The Singer’s Formant is the peak of sound energy in the 3 kHz to 4 kHz frequency range found uniquely in professional opera singers’ voices (and not in amateur voices), which allows their sound to project over an orchestra (whose sound energy tapers off above 3 kHz). The tenor Jussi Bjoerling was a singer whose formant allowed his seemingly smallish voice to carry over an orchestra. This may also explain why Bjoerling and Pavarotti’s voices record so well. - Wah Keung Chan