The vocal tract involvement
Singing entails vibration of the vocal cords. The two lower voices, bassu e contra (in some case the mesu boghe as well) have particular laryngeal contraction that brings, in the case of the basso, to a specific acoustic effect, which is a doubling of the period (i. e. a lowering of the pitch of one octave) and a particular roughness of the timbre. In the case of the contras, the larynx contraction does not imply the doubling of the period, but gives the timbre a particular flavour.
A correct synchronization of singing and breathing is important in order to maintain the cohesion with the other singers of the choir. Singers do not do any preliminary exercises before singing, but consider well-being, ease and fit to be essential to a good performance.
Vocal timbres are crucial in the esthetic of the a tenore song. Particular non-sense syllables are characteristic of some village styles, areas, or songs. Generally speaking, the timbre of the vowels have the greatest importance in the songs in free rhythm, and the overall quality of the voice of the singer is one of the most important elements in the individual characterization of the voices. The vowel duration is usually shorter in the rhythmic songs (dances, mutos): in these cases, the role of the consonants is crucial.
Depending on the role of the singers, the vocal qualities required from the singers are different. The bassos and the contras must be able to use properly the contraction of the voice (only some manage to do this as expected); the boghes and the mesu boghes shall have a good vocal timbre, ability to improvise and vibrate and modulate the voice according to the singing style. A good command of pitch is crucial for all singers. In particular, the boghe must be able to chose the exact overall intonation (in recent years, some professional group used a diapason to that end, but this is considered by many a questionable practice). The ability to perform in chord polyphony is an essential requirement for the singers of the choir.
 Bailly, L., Heinrich, N., & Pelorson, X. (2010). Vocal fold and ventricular fold vibration in period-doubling phonation: Physiological description and aerodynamic modeling. J. Acoust. Soc. Amer., 127 (5), 3212-3222.