Why do singers use vibrato?
Dear Straight Dope:
Why does a gifted singer often lapse into a vibrato (wavering tone) after a few seconds of holding a long note? Is this a natural tendency or is it done for effect? I think the mark of a good singer should be the ability hold a steady note, without wavering between sharp and flat.
I bet you're thinking of "I Will Always Love You," sung by Whitney Houston. Am I right? If not, did I put that song into your head? I love to do that. Short answer: it's done for effect. Hostile answer: you are an uncultured philistine, and probably pick your toenails at the opera. Long answer: hey, that's why I took this gig in the first place.
Anyway, first there's gotta be a clarification of terms. And not just for you, but for the whole music community. A true vibrato is, as you describe, a fluctuation in pitch. The best demonstration of this is what good string players do, that is, rapidly move the left hand on the fingerboard so the pitch moves minutely up and down. On a bowed, and to a lesser extent a plucked, string instrument, this is done to lend a . . . I dunno, I guess a 'warmth' to the tone that doesn't come from simply bowing the string. In the 20th century, this has become such a common feature of playing that composers will write senza (without) vibrato on passages they don't want played that way, the implication being that the music should be played with vibrato at all other times.
Vibrato may be achieved in several ways on a wind instrument. The speed of the airstream can be varied, which produces a fluctuation of intensity or dynamics, which is more accurately called a "tremolo." A tremolo on a string instrument is played by rapidly moving the bow back and forth across the string. A wind player can also alter the embouchure (the manner in which the lips and tongue are applied to the mouthpiece of the instrument) by tightening facial or tongue muscles. This can change the tone as well as the pitch and dynamic of the instrument, but results in a more noticeable 'shake' than a string vibrato. A trombone, obviously, can much more readily approximate a string vibrato by moving the slide, having access to microtones not easily available from other wind instruments. Finally, a brass player in particular may achieve a vibrato by shaking the instrument itself, or changing the shape of the air column by rapidly muting and opening the bell of the instrument.
Last (discounting percussion, where vibrato is not typically controlled by the performer), we have vocalists. The thing about singers is they can easily alter the pitch or dynamic of a note, or change the tone without changing either one. However, as I say, it takes incredible skill to do this right. Opera singers, playing with pit orchestras that always include strings, have taken their cue to add vibrato to their singing whenever possible. However, the best approximation of a bowed string instrument, most authorities agree, is not a vibrato (pitch shake) but a tremolo (volume shake). A heavy vibrato, once necessary to make one's voice recognizable in a large room, accompanied by a full orchestra, now stands out in these days of great acoustics and microphones, as an extreme fluctuation of pitch, to the point that the actual pitch is obscured. Cynics like yourself might say that's the idea. However, a tremolo, raising and lowering the intensity of the voice without changing pitch, is still considered a welcome addition to a singer's repertoire.
Yes, a good singer CAN hold a note steady, and adds the tremolo for effect. If there's a few cents difference in pitch, that doesn't detract from the quality of the performance. Whether it's an actual warmth added to the sound, or whether we're just conditioned to think so, a well done tremolo (popularly referred to as a vibrato) is the mark of an accomplished singer.