In his Observations on the Baroque and Modern Vibrato, in which he pays homage to the limited-vibrato proponent Moens-Haenen, Frederick Gable explains that vocal vibrato is the body's reaction to muscular tension in vocal production. (3) As a vocalist raises the volume of a tone, the muscles tighten and release at a regular interval to reduce tension and allow the tone to be sustained for a longer period of time. This action produces fluctuation of both intensity and pitch. He goes on to assert that a wider "natural" vibrato has been created in the 20th century due to the demands of "continual loud singing needed in large opera houses and for being heard over a 20th century orchestra". (4) This vibrato then becomes learned and translated to all dynamic levels. In the Baroque period, the lack of these demands facilitated a "natural" vibrato that Moens-Haenen characterizes as narrower and less obtrusive. (5) One must wonder, however, whether or not this narrower, less obtrusive vibrato that Gable advocates is possible if a particular 20th century performer wishes to sing anything but early music.
Frederick Neumann responds to this question of the 'obtrusiveness' of a wider vibrato in terms of the sonance phenomenon. In his Performance Practices of the 17th and 18th centuries, he describes sonance: "...the vibrato oscillations...are fused into the sensation of a richer tone as the perception of the oscillations diminishes". (6) In short, our ears synthesize the pitch fluctuation of a particular vibrato into one warmer, richer tone. Similarly, Robert Donington addresses the need for vibrato from the listener's perspective in that the ear becomes easily fatigued of a constant, straight tone. (7) Gable responds to this by arguing that what sounds "straight" to a modern ear actually has small pitch fluctuations in it-- this is the "natural" vibrato employed during the Baroque period. This narrower "natural" vibrato allows a performer or ensemble to create a more brilliant and distinctly "Baroque" sound. Again, the question remains: how does one reconcile this with the fact that some 20th century audiences and therefore some 20th century ears may not be receptive to this Baroque sound? Are they deemed "unworthy" of the privilege of listening to early music because of their aversion to historical performance practice? It seems that too few musicians have deemed the question itself worthy of asking.
3. Gable, p. 93
4. Gable, p. 93
5. As interpreted by Gable, p. 91
6. Neumann, Performance Practices of the Seventeenth and Eighteenth Centuries, p. 499
7. Robert Donington, as quoted in Gable (full text), p. 98