Monday, May 01, 2006

Bernoulli, Doppler and Natural Vibrato

A number of students have asked me to teach them how to "belt". Apparently, belting is a term having to do with singing musical theater songs in keys that are just high enough to make listening painfully impossible to avoid at any distance. I call it by it's true name, "yelling" and explain that the range of a voice is measured in octaves and intervals and not in yards. The singers who attempt this sort of material without the proper background usually have a mistaken concept about volume, and horrifying breathing technique not unlike the forced wheeze of an old accordian...well hell, a new accordian for that matter. I'm not bad-rapping accordians, but they aren't a good mechanical example on which to model any sort of vocal technique. But the one vocal characteristic which forces me to make damn sure the dairy products are properly stowed in the refrigerator before the "belting" begins is the vibrato. It is too wide, too slow, too fast, flat or sharp. It is always conspicuous but never pleasing, It is a widely misunderstood thing, this vibrato, and it will turn a three minute song into an hour at the metal shop if it isn't atended to.

True vibrato is a shimmer, a patina on the voice, nothing more. True, a vibrato can be manipulated for effect, but this should be a matter of choice and not a lack of technique. Skeptic that I am, and trusting my instinct, I've come to believe that true, natural vibrato is the result of the Bernoulli effect and the Doppler effect as they occur within the singer's throat. Yeah, this may get real boring, but this is the shit that keeps me up at night when TNT runs out of "Law and Order" re-runs.

Now, the Bernoulli effect is what keeps airplanes in the air. Very simply, if you blow air across a surface, the surface will be pulled toward the flow of air. You can demonstrate this by holding a small piece of paper as if you were going to give yourself a paper cut across your lower lip. Now blow. the paper will rise and be pulled into the air flow. Think of your vocal cords as two pieces of paper facing each other. When an air flow is passed through the gap, the cords are pulled into the flow and toward each other. the natural tension on these opposing membranes pulls them back, away from the flow. This is called "Phonation" and when this cycle of events occurs 440 times per second, the note "A" is produced.

The Doppler effect is best illustrated as that thing that happens when a train goes by and the "ding ding ding" get's higher in pitch as the train approaches and lower in pitch as the train gets farther away. If Phonation occurs in a relaxed throat, with no undue tension , the Doppler effect will come into play and cause the vibrato, or shimmer. The vocal cords, being pulled toward each other into the airflow, are also being pushed by the flow ever so slightly up, toward the mouth. Being the delicate membranes that they are, and being under tension, they fight that tension and relax back, away from the mouth. This tension and relaxation cycle shifts the point of phonation closer then further from the mouth and again, given a relaxed throat, this shift back and forth creates a regular, almost imperceptible modulation in pitch and intesity which we know as the vibrato.

A masterful singer can manipulate the tension to make the vibrato more pronounced or disappear completely. Check out Joni Mitchell on the "Miles of Aisles" album. At the end of "Love or Money" she slowly takes the vibrato out of the last note to match Tom Scott's saxophone...brilliant detail.

Well, that's my rant of the day, Sometime soon, I'll try to explain the whole inter-costal, diaphramatic breathing thing. In the meantime, ask a lot of questions, and remember that it's always simpler than it seems. Cheers.


boulejazz said...

I haven't thought about the "Miles of Aisles" album in quite a while. It could be the best sounding "live" album I've ever heard. I'd love it if Joni Mitchell would go out on tour just one more time with the L.A. Express.

Gustavo Lacerda said...
This comment has been removed by the author.
gustavolacerda said...

I doubt the Doppler effect in your throat could be strong enough to be noticeable. For the first frequency doubling (octave), you'd need the sound source to be moving at half the speed of sound (i.e. v = 1/2 c). To triple the frequency (i.e. lambda = 3), you'd need it to move at 2/3 the speed of sound. In general, 1/lambda = 1-v/c, or v = c (1 - 1/lambda).

If we take the minimal noticeable change to be 20 cents (where 1200 is an octave), lambda = 1220/1200 = 61/60.
Thus v = c (1/61) = 1/61*340m/s ~= 5.57 m/s .

I don't think throats reach that speed when they vibrate.

singing cave said...

I agree that the bernoulli effect is involved, but not the doppler effect.

But I liked this post. It was interesting and informative.