More questions than answers about vibrato at Musical Crematorium. I'm especially concerned with the New Harvard Dictionary's definition, which seems to imply that vibrato is something that a singer does and uses. It's maybe a little irresponsible to offer the view that a singer adds vibrato to his singing the way that a violinist makes the conscious effort to fluctuate the pitch in order to enrich the sound.

I am pleased to see, though, that the student blogger (DepauwDiva) is circumspect enough to take in other sources, including Mozart himself, that recognize vibrato as a natural vocal function. She also cites Cornelius Reid, author of arguably the most important books in the 20th century vocal pedagogy canon. Reid's early statement sees vibrato as a mystery, but in his later book, Free Voice: A Guide to Natural Singing, he expounds on his former position. Regrettably, it seems the student never got around to reading it [I can't blame her; it's quite technical, lofty, and not for those easily confused). Still, it remains, in my overeducated experience, the most likely and logical mechanical explanation for the phenomenon of the vibrato:

"After the pressure of the breath against the stretched vocal cords has set them into vibration an unusual action occurs. Instead of remaining in a fixed position of vibratory tension the cords yield somewhat to the breath pressure exerted beneath them so that the air escaping from the lungs is released in a series of puffs. With each puff the chords spread apart momentarily; then, after the briefest interruption the opening immediately closes as the cords in an undulating motion return to normal position.

With the vocal cords the upward and outward movement followed causes a slight raising of the pitch to take place. With the reduction of breath pressure made possible by the escape of each puff of air this change is straightaway counteracted by a lowering of the pitch as the vocal cords spring back to their normal position. During the return of the cords to the normal position the mean pitch is exceeded, so that when a tone is sustained a series of rapid pitch fluctuations take place whereby the tone that is heard actually represents the center point of a rapid alteration between an imperceptibly raised peak and a slightly lowered depression. One of the most important features of this phenomenon is the regularity of its occurrence, both in amplitude, that is to say, in width of pitch change, and in periodicity, or the number of oscillations per second. The action just described is heard in singing as a vibrato."

You can purchase Reid's books from Jospeh Patelson Music House.