Contestant Susan Boyle became an Internet sensation this week after her show-stopping performance on Britain's Got Talent. Boyle's voice, despite limited previous training, is powerful and features an intense vibrato—that warbling you hear in professional singing voices. Can anyone sing with vibrato?
Yes. If you loosen your throat muscles and force air through your vocal tract, then your larynx will oscillate, creating a warbling effect. In more detailed terms, that means relaxing the muscles you use to swallow, letting your tongue sit loose, and keeping your throat expanded. For some people, that amount of relaxation is difficult—after all, talking keeps the throat muscles relatively tight. For others, the balance of breathing, abdominal support, and throat control comes fairly naturally.
Some musical styles are heavier on vibrato than others. Classical singers often use lots of vibrato, in part because the notes tend to be quite long. (If a note is held for an extended period of time, it can sound flat or boring without vibrato.) Another reason is volume: Vibrato is often a byproduct of singing loudly, so you're likely to hear it when an opera singer belts over an orchestra without a microphone. Pop singers use this technique less often, in part because recording microphones don't always respond well to vibrato. But some popsingers will start a note on a straight tone and switch to vibrato at the end—think Whitney Houston's "Iiiiiiiiiieeeeaaaaaayyyyeeee" in "I Will Always Love You." Britney Spears deploys the technique on occasion, although she doesn't have strong vibrato. Mariah Carey, on the other hand, does.
The speed of vibrato can vary. When done right, the larynx will vibrate between 4.3 and 7.2 oscillations per second. (Some say the oscillations can go up to 9.) With a slower rate, you'll sound like a warbling grandma. With a faster rate, your intended vibrato will sound like a trill. Some musicians, like Edith Piaf or Joan Baez, make fast vibrato their trademark. Others, like opera singer Maria Callas, develop a warble late in their careers. (As singers age, they often find it more difficult to control their throat muscles.) Vibrato can also vary by amplitude. For an opera singer with a "wide" vibrato, the pitch might range as much as a fifth—a pretty big interval—from top to bottom. More subtle vibrato might oscillate between two adjacent notes.
It's possible to fake vibrato. One common method is to consciously alternate between two nearby notes, starting slowly and speeding up until you produce a warble. (See a demonstration here.) You can also do what's called a "diaphragmatic vibrato," in which you make your abdomen pulsate during a sustained note. Voice coaches use both of these techniques to teach aspiring singers how to produce a natural vibrato. But it's easy to tell when someone's faking it—it just sounds forced.
Instruments can also produce vibrato. A violinist achieves this effect by moving her left hand back and forth above the fingerboard while pushing down on the string. Trombonists move the instrument's slide back and forth. Oboe players produce vibrato by adjusting air flow and embouchure, or the shape of their lips. Trombonists move the instrument's slide back and forth and use their lips and diaphragms as well. * Vibrato is impossible on most keyboard instruments, since you usually can't affect the sound of a note once it's struck. One exception is the clavichord, on which it's possible to adjust the sound of a note even after you've hit the key.
Vibrato has not always been as popular as it is today. During the Baroque and Renaissance periods, vibrato was used only for occasional ornamentation. That continued into the 19th century, when prominent violin theorist Pierre Baillot used vibrato sparingly in his compositions. Only in the 1920s, when musical recording took off, did classical musicians start using vibrato near-constantly. Some believe vibrato sounds better than straight tones in big concert halls. Others say vibrato was a response to the rise of equal temperament—a tuning system in which every pair of adjacent notes has an identical frequency ratio.
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Explainer thanks Ross Duffin of Case Western Reserve University, Maitland Peters of the Manhattan School of Music, David Sabella-Mills of the New York Singing Teachers' Association, and Kevin Wilson of the Boston Conservatory.
Clarification, April 21, 2009: This article originally suggested that trombones produce vibrato using the slide alone. (Return to the revised sentence.)