Vibrato is not really a requirement for a trained voice, it generally occurs naturally, and it's produced by a combination of forces at work when a person sings—or speaks, for that matter. But when one is speaking, the duration of a single tone is usually so short that the vibrato present is not noticeable. I've taken lessons from three different voice teachers, and none of them tried to get me to develop a vibrato. I never even thought about vibrato, but when I listen to tapes, I notice that I do have a bit of it. It just happens. I could suppress it, but when I do, it feels unnatural. Why bother? No one has ever mentioned it to me, and I don't notice it unless I'm specifically listening for it. And most of the singers—not classically trained—that I know, or hear on records, also have at least a touch of vibrato.

With some singers, the periodicity and the width of variation can get out of hand ("wobble") and it becomes very conspicuous. This is not good. A natural vibrato, other than giving the voice "life," should hardly be noticeable. But—if you listen specifically for vibrato, you're bound to hear it in all but a very few singers. And I guess that sometimes that can spoil the experience. It's sort of like "Whatever you do, don't think of an elephant!" When someone, a classical singer for example, opens his or her mouth to sing, you expect to hear vibrato and, son-of-a-gun, that's all you hear.

It's not that opera singers necessarily have more vibrato than other singers, but often they are trying to sing over a whole symphony orchestra, and because they are so bloody loud (not everyone has a big enough voice for this kind of singing), it may become more noticeable. I heard Dennis Bailey, a tenor with Seattle Opera a few years back, sing in a relatively small meeting room, and I was astounded at how loud his voice was. And I've heard that in similar venues, Renée Fleming (not a big woman) can practically blow the walls out if she's a mind to.

As a matter of fact, I'm listening to Renée Fleming right now, on the Metropolitan Opera broadcast of Manon. Her vibrato is there—if I focus on it. But I can't trying to imagine her voice without it. It would sound flat and lifeless. Ah! Here comes the tenor. Him, too.

Vibrato seems to be regarded by most musicians—and audiences—as a desirable thing. Almost all instrumentalists try for vibrato. Watch a violinist. Notes will be emphasized by undulating the left-hand to give the fingered note an up-and-down variation in pitch, with very good effect. Violinists use it almost all the time. Or classic guitarists. Hard to do on steel strings, but on nylon strings it works. Some electric guitars come equipped with a vibrato arm. Popular singers often come at a note "straight" (no vibrato) and a little under the correct pitch, come up to the correct pitch, and add vibrato. Also a very good effect.

Unless it develops into a wobble, it doesn't pay to try to suppress a natural vibrato. Trying to prevent one's voice from doing its natural thing develops undue tension that can result in nodes on the vocal folds. On the other hand, I recall a fairly promising coloratura soprano who lived around here some years back. Her voice teacher—who was also her mother (bad combination, especially since she was a stage mother!)—thought to give Leone a unique voice by getting her to develop a strong vibrato. The ultimate result was that Leone wound up sounding like a bleating goat when she sang. Nice voice to begin with, but it became downright irritating to listen to, and she went nowhere fast.

There is a pretty good rundown on vibrato here:    Clicky #1. Note where the writer points out that, although some choir directors want their singers to sing with a "straight tone" (no vibrato), singing that way can be damaging to the voice. And Wikipedia has a good article on vibrato in both instrumental and vocal music here:    Clicky #2.

If you listen for vibrato in the voices of various folk singers (including traditional singers, not just Joan Baez), you'll notice that a lot of them have at least some. As I mentioned above, Ewan MacColl has a very strong vibrato. Doesn't bother me. That's just part of his natural sound, and it wouldn't sound like Ewan MacColl without it.

Don Firth