gradually becoming louder then softer

The art of increasing and diminishing the tone on a single note, it is an important indication of a singers vocal technique and control.

A tone begun softly, which is then swelled into a crescendo, and then back in a descrescendo. (Not to be confused with mezza voce, or, half voice.) In the 19th century it was a "must" for singers of Italian bel canto operas. Nowadays it is not so common - few singers have the technique to do it. It requires complete control over the dynamics of the voice. You can read more about the technical aspects of the messa di voce at La Scena Musicale . Example: Bellini: I Puritani - excerpt from Elvira's "Vieni al tempio" aria in Act I (from the CD NC 170562-2) The context: Elvira has just discovered that her fiancé has left her, minutes before the wedding ceremony. She loses her reason because of the shock. In the aria she fantasizes about the wedding ceremony. The messa di voce toward the end conveys the great pain felt by the abandoned young woman.

moderate swell.