Chest Voice & Head Voice

Chest voice is a term used within vocal music. The use of this term varies widely within vocal pedagogical circles and there is currently no one consistent opinion among vocal music professionals in regards to this term. Chest voice can be used in relation to the following:

• A particular part of the vocal range or type of vocal register
• A vocal resonance area
• A specific vocal timbre

Psysiological process

As the opinions on what exactly chest voice is vary greatly, there is no one consensus on the physiological production of chest voice. Here are a few opinions:

Bel canto understanding

This view understands chest voice as the vocal register used within normal speech. It was discovered via stroboscope that during ordinary phonation, or speaking in a man the vocal folds contact with each other completely during each vibration closing the gap between them fully, if just for a small length of time. This closure cuts off the escaping air. When the air pressure in the trachea rises as a result of this closure, the folds are blown apart, while the vocal processes of the arytenoid cartilages remain in apposition. This creates an oval shaped gap between the folds and some air escapes, lowering the pressure inside the trachea. Rhythmic repetition of this movement a certain number of times a second creates a pitched note. This is how the chest voice is created.

Vocal resonance understanding

This view believes that the chest voice is a product not of vocal registration but vocal resonation. Opinions within this understanding vary. Although some pedagogists believe the chest is an effective resonator, most agree that chest voice actually resonates in the head while creating vibratory sensations in the chest. Tarneaud says,

"during singing, the vibration of the vocal folds impresses periodic shakes on the laryngeal cartilage which transmits them to the bones in the thorax via the laryngeal depressors, and to the bony structures in the head via the laryngeal elevators. Singers feel these shakes in the form of thoracic and facial vibrations".

These internal phonatory sensations produced by laryngeal vibrations are called "resonance" by singers and teachers of singing.

During singing in the lower register, the larynx is lowered since the muscles which connect it to the rib cage are tensed whereas the muscles above the larynx are not tensed. Consequently, a large proportion of the vibratory energy is transmitted to the thoracic area, giving singers the impression that their voice is resonating in the chest. This impression however is false. The chest by virtue of its design and location can make no significant contribution to the resonance system of the voice. The chest is on the wrong side of the vocal folds and there is nothing in the design of the lungs that could serve to reflect sound waves back toward the larynx.

The chest register is the normal vocal range of a singer. When you speak you are in chest voice. So, singing in chest voice is just speaking, sustained. The voice tone of chest voice is fuller and louder than head voice or falsetto, because the vocal chords are thicker and can withstand a lot of air pressure, thereby producing a strong sound wave. When you start singing higher in pitch, in chest voice, you with either have a feeling of wanting to flip into falsetto, or you may have had voice training and are able to belt. Chest voice has a speech quality to it and is used by every artist popular music performance especially RnB and Rock. You are less likely to hear a female opera singer, expecially a soprano, using chest voice. Singing in chest voice is a good way of letting go and singing your heart out but voice training is essential if you are to use it properly!

Head voice is a term used within vocal music. The use of this term varies widely within vocal pedagogical circles and there is currently no one consistent opinion among vocal music professionals in regards to this term. Head voice can be used in relation to the following:

• A particular part of the vocal range or type of vocal register
• A vocal resonance area

Head voice and vocal registration

One prevailing practice within vocal pedagogy is to divide both men and women's voices into three registers. Men's voices are divided into "chest register", "head register", and "falsetto register" and woman's voices into "chest register", "middle register", and "head register". According to this practice, singing in the head register feels to the singer as if the tone is resonating in his or her head (rather than primarily in the chest or throat). According to an early 20th century book written by David Clippinger, all voices have a head register, whether bass or soprano.

Clippinger claims that males and females switch registers at the same absolute pitches. He also states that at about E flat or E above middle C the tenor passes from what is usually called open to covered tone, but which might better be called from chest to head voice. At the same absolute pitches the alto or soprano passes from the chest to the middle register. According to Clippinger there is every reason to believe that the change in the mechanism for male voices into head register is the same as that which occurs in the female voice as it goes into the middle register at the same pitches.

The contemporary vocal pedagogy instructor Bill Martin seconds the view that the change from chest voice to head voice occurs at around E4 in all voices, including the bass, but Martin states in the coloratura soprano it is more likely to occur at F4. A recent book by a former teacher at Oberlin College Conservatory of Music and a vocal pedagogy teacher, Richard Miller; states that in the "tenore lyrico" the higher part of the singing voice above the secondo passaggio at G4 extending upwards is referred to as "full voice in head," or voce piena in testa, effectively stating the head register begins at G4 in the "tenore lyrico," not at E4. According to Singing For Dummies, the bass changes from chest voice into head voice around A3 or A♭3 below Middle C and changes into his falsetto voice around D4 or C♯4 above Middle C.

In the head register (which is above the chest register), some of the bottom end leaves the voice, but it's still, according to Martin, a voice capable of much power.

Explanations for the physiological mechanisms behind the head voice can alter from voice teacher to voice teacher. This is because, according to Clippinger, "In discussing the head voice it is the purpose to avoid as much as possible the mechanical construction of the instrument".

However, not all vocal teachers agree with this view. Thomas Appell's 1993 book Can You Sing a HIGH C Without Straining? aimed to refute the theory that all singers switch registers at the same absolute pitch. Appell defined chest voice as resonance below the vocal folds and head voice as resonance above the vocal folds. He recorded examples of male and female singers changing from chest voice to head voice at different pitches in an attempt to prove that the transition pitch is a function of the intensity of the vocal tone and is not absolute. At higher vocal cord tension (intensity of singing), Appell shows that the pitch at which a singer transitions from chest to head voice will be higher. At lower vocal cord tension (intensity of singing), Appell shows that the pitch at which a singer transitions from chest to head voice will be lower.

Head voice and vocal resonation

This view believes that since all registers originate in laryngeal function, it is meaningless to speak of registers being produced in the head. The vibratory sensations which are felt in the head are resonance phenomena and should be described in terms related to resonance, not to registers. These vocal pedagogists prefer the term "head voice" over the term register and divide the human voice into four registers: the vocal fry register, the modal register, the falsetto register, and the whistle register. This view is more consistent with modern understandings of human physiology and in keeping with stroboscope videos of laryngeal function during vocal phonation. Tarneaud says, "during singing, the vibration of the vocal folds impresses periodic shakes on the laryngeal cartilage which transmits them to the bones in the thorax via the laryngeal depressors, and to the bony structures in the head via the laryngeal elevators. Singers feel these shakes in the form of thoracic and facial vibrations". These internal phonatory sensations produced by laryngeal vibrations are called "resonance" by singers and teachers of singing.There are seven parts of the human body that act as resonators and of those seven the three most effective resonators that help amplify and create the most pleasing sounds are all located in the head: the pharynx, the oral cavity, and the nasal cavity.

Not falsetto

Resonances and registration aside, the term "head voice" is commonly used to mean "high notes that are not falsetto or strained". For example when Pavarotti or Stevie Wonder slides from chest voice to a high C5 in full, balanced voice, this is referred to as "head voice".
Beginning singers who have difficulty controlling their vocal break need to be taught to eliminate and/or control the physiological conditions associated with falsetto or strain, and "head voice" is a term used to describe this process. A strong falsetto is called a reinforced falsetto and a very light head voice is called voce di testa bianca or 'white head voice'.

High notes that are sung with balanced physiology do tend to have better resonance than falsetto or strained notes, so this definition does not usually contradict the other two.

Chest Voice

A singer's normal speaking voice, when sustained in a single note is referred to as 'chest voice.' Put your hand on your chest and say the word 'at.'

Now make the 'aaa' last a long time--'aaaaaaaaaaat'

You'll feel the vibration in the chest. So 'chest voice' is a reference to the dominant resonance cavity -in this case, the chest.

In Chest Voice the vocal cords come together with a good firm seal and vibrate along their entire length as the air flows between them. This is the lower part of your vocal range.

As the singer climbs into higher notes, the cords begin to tighten (like a guitar string when you turn the tuner peg). At some point, the cords reach a crisis-- they can only stretch so tight before they risk damage. 

If the singer tries to keep this chest voice going ever higher, the cords will preserve themselves by suddenly breaking apart, dumping the extreme tension, and producing the next higher note via 'falsetto.'

Since vocal cords are made of muscle, they can do things a guitar string could never do.

In this case, in addition to breaking apart to relieve the pressure from the lungs, they actually change their thickness (they thin themselves out--the equivalent to changing to a thinner guitar string in middle of a song to reach a higher note!) 

The problem is that the tone goes from firm and rich (chest voice) to something thin and airy and light (falsetto) in the space of only one note. This is fine as a sound effect, but it is the cause of much frustration for singers everywhere. We all wish we could just reach one or two notes higher with that rich, firm chesty tone! But alas. 

But there is great news! There are simple exercises that can cause the singer to release the tension and NOT go into falsetto in these higher notes.

A singer can eventually 'FADE' from chest voice into a firm upper range called 'head voice.' 

Head Voice

The term 'head voice' refers to the fact that on higher notes, the tone begins to resonate more in the small spaces of the head (nasal and sinus cavities).

We'll talk more about the effect of resonance on tone in later issues of 'vocal tips,' but for now, let's talk about what the cords are doing.

They are doing something VERY different between falsetto and head voice. 

In head voice, the cords remain in contact with one another. This makes a huge difference in tone between falsetto and head voice. The head voice sounds clear and 'clean' without the excess 'airy' sound, because there is no escaping excess air.

In the male singer, the chest voice 'crisis point' is around the notes E, F, F-sharp, or G above middle C. In the female, it's at A-flat, A, B-flat, or B above middle C. (Incidentally, the female FIRST crisis point is the male SECOND crisis point). If the singer has learned how to 'FADE' into the next register (head voice), there will be no breaking apart of the cords for self-preservation. They do something wonderful---

They first thin out (like falsetto) but they stay together as they thin. 

Eventually, up toward the very highest notes, they not only thin out, they partially 'ZIP UP' like a guitar string being 'fretted.' This all has the effect of keeping the tone clear (because the cords stay in good contact with one another) AND, more importantly, the cords are not required to tense ever tighter to reach higher notes!

This is huge!

The cords are designed to close themselves off on higher notes so that they don't have to be stretched to the point of injury to reach those notes. 

Head voice is a beautiful, clear sound, rather than the airy falsetto sound.

The best news of all is that there are exercises that can teach a singer to MIX chest voice with head voice as the singer goes higher. And they are NOT difficult exercises at all!

Eventually, a listener will hear a singer go from chest through a 'mixed' area into a pure head voice and it will sound like ONE HUGE SINGLE VOICE!

By huge, I mean huge-sounding because it will be rich in tone, like chest voice. But I also mean huge in range!

I personally have nearly a 4 octave range. Brett has a consistent 5 octave range and on certain days has over 6 octaves with no 'breaks!'

Most of his students grow to 4 octaves and more!

Many people are skeptical when they hear this, because the normal experience of most singers is about an octave and a half before they MUST either stop going higher or break into falsetto.

Two of the most commonly used term in singing circles are “Chest Voice” and “Head Voice”. If you’ve always wondered what this actually means, read on….

In the “chest voice” - the voice most people use to speak with - people generally feel the resonance of pitches in that area vibrating in their chest. Put your hand on your chest and say the vowel “a” as in “cat” nice and strong - feel how that seems to resonate between your throat and chest? That’s your chest voice. Then cheer saying, “Woo-hoo!” - feel how the sound seems to have moved into your head? That’s your head voice.

Now for a more technical explanation: how do the vocal folds work? If you’ve ever seen a picture of the vocal folds in action you’ll see that they are attached at one end in a “V” shape and vibrate together, with the help of breath, along their length to create pitch. (See link below to view video of vocal cords in action). At the pitch “A 440″ (the pitch orchestras tune to) the vocal folds are coming together 440 times/second to create that pitch (the note you hear). Lower pitches have a lower number and pitches up in a singer’s “whistle-tone” register (think Mariah Carey) are vibrating in the 3000′s. When a singer is vocalizing in their chest voice the vocal cords are using their thickest width to create the pitches in that register. Then, at a certain point, the vocal cords have to make a physical shift to reducing the vibrating mass and thickness to create higher pitches. What that means is that the vibrating portion of the vocal folds that is involved in creating the pitch must thin out as the pitches get higher.  Think about how you change pitch with a rubber band.  The lower the desired note, the thicker the vibrating mass of the band will be; the higher the desire pitch, the more you will stretch the band.  Similarly, the voice needs to make a shift to a thinner coordination in the vocal folds as the pitch ascends.  When it comes to bridging from chest to head voice think of the same rubber band experiment:  except that you can only stretch the rubber band so far before you hit a ceiling or break the band (top of your chest voice).  Now stretch the rubber band, but this time, place one finger in the middle of the stretched portion and play the pitch.  Now you’ve “bridged” the band and suddenly have many more higher pitches available without over-straining the vibrating mass.  Do this earlier and you eliminate the chances of breaking the rubber band - or straining your voice.

The first transition or bridge (also known as passagio), between chest and head voice, generally happens around an E-F# above middle C4 for men and around an Aflat-Bflat above middle C for women. Every singer I’ve ever encountered in my studio struggles at the beginning with either their first or their second bridge, though the first bridge transition is the most common struggle. (Every 4th or augmented 4th interval contains another of these bridges.)

Classical and choral singers tend to sing mostly in their Head Voice. Rock/pop and Musical Theater singers tend to sing in their chest voice without transitioning to a thinner cord, though some can sing in “Mix”, sounding like they are effortlessly taking their chest voice higher in their range. When a singer connects seamlessly between chest voice and head voice, maintaining a consistent tonal quality throughout this transition, this is referred to as “Mix” - which is just that: a comfortable mix of the elements of chest voice and head voice.

The biggest problem among singers isn’t being able to hit those higher notes, hold a note for longer, or deliver more volume. It is something much more complicated and tricky: blending or “bridging” their chest voice and head voice.

Head Voice vs Chest Voice

The head and the chest are the two most common resonating areas. Try placing your hand on the top part of your chest (your sternum, or breastbone) and singing a note from the lower end of your range. Can you feel a slight vibration? Now, try singing in a high pitch. Where is the vibration now? It should feel as if the vibration is in your eyes, nose, even your forehead.

This is because your chest voice and head voice are actually in different registers. When you produce sounds that resonate in the top of your chest or throat, your vocal cords vibrate along their full length, produce long sound waves of a low pitch. When you produce sounds that resonate in your head, the ends of the vocal cords close off until only one-third their length is free to open and close. As a result they move much more rapidly, producing short sound waves of a high pitch.

You also have a middle voice. This is when about half the length of your vocal cords is free to vibrate. The best singers can move seamlessly between their chest voice, middle voice, and head voice. When you can do this, your voice is said to be connected.

You can think of the range from head voice to chest voice in this way.

1. twang
2. opera
3. sob
4. belt
5. speaking

The top represents the strongest head voice, while the bottom of the list, your speaking voice, is almost entirely a chest voice. Some think of the middle voice as somewhere between #3 and #4—an excited and forceful sob, or a softer belt. Notice that the “type” of voice does not have a direct relationship to how high or low you are singing. You can sing the exact same pitch with your chest or your head voice. However, each type of voice adds a different quality to your singing.

Source:

http://en.wikipedia.org/wiki/Chest_voice

http://en.wikipedia.org/wiki/Head_voice

http://www.singingfreedom.com/singing-lesson/chest-voice-training.php

http://www.theconnectedvoice.com/V2/2010/03/02/chest-voice-and-head-voice/

http://www.starsinginglessons.com/the-difference-between-chest-voice-and-head-voice.php

http://www.become-a-singing-master.com/head-voice-and-falsetto.html

Falsetto

Falsetto (Italian diminutive of falso, "false") is the vocal register occupying the frequency range just above the modal voice register and overlapping with it by approximately one octave. It is produced by the vibration of the ligamentous edges of the vocal folds, in whole or in part. Commonly cited in the context of singing, falsetto, a characteristic of phonation by both men and women, is also on speech pathology.
The falsetto voice—with its characteristic breathy, flute-like sound relatively free of overtones—is more limited than its modal counterpart in both dynamic variation and tone quality. The term falsetto is most often used in the context of singing to refer to a type of vocal phonation that enables the singer to sing notes beyond the vocal range of the normal or modal voice

Physiological process

The modal register, or normal voice, and falsetto register differ primarily in the action of the vocal cords. Production of the normal voice involves vibration of the entire vocal cord, with the glottis opening first at the bottom and then at the top. Production of falsetto, on the other hand, vibrates only the ligamentous edges of the vocal folds while leaving each fold's body relatively relaxed. Transition from modal voice to falsetto occurs when each vocal cord's main body, or vocalis muscle, relaxes, enabling the cricothyroid muscles to stretch the vocal ligaments. William Vennard describes this process as follows:

“With the vocalis muscles relaxed it is possible for the cricothyroids to place great longitudinal tension upon the vocal ligaments. The tension can be increased in order to raise the pitch even after the maximum length of the cords has been reached. This makes the vocal folds thin so that there is negligible vertical phase difference. The vocalis muscles fall to the sides of the larynx and the vibration take place almost entirely in the ligaments.”

In the modal register, the vocal folds (when viewed with a stroboscope) are seen to contact with each other completely during each vibration, closing the gap between them fully, if just for a very short time. This closure cuts off the escaping air. When the air pressure in the trachea rises as a result of this closure, the folds are blown apart, while the vocal processes of the arytenoid cartilages remain in apposition. This creates an oval-shaped gap between the folds and some air escapes, lowering the pressure inside the trachea. Rhythmic repetition of this movement, a certain number of times a second, creates a pitched note.

In falsetto, however, the vocal folds are seen to be blown apart and in untrained falsetto singers a permanent oval orifice is left in the middle between the edges of the two folds through which a certain volume of air escapes continuously as long as the register is engaged (the singer is singing using the voice). In skilled countertenors, however, the mucous membrane of the vocal folds contact with each other completely during each vibration cycle. The arytenoid cartilages are held in firm apposition in this voice register also. The length or size of the oval orifice or separation between the folds can vary, but it is known to get bigger in size as the pressure of air pushed out is increased.

The folds are made up of elastic and fatty tissue. The folds are covered on the surface by laryngeal mucous membrane which is supported deeper down underneath by the innermost fibres of the thyroarytenoid muscle. In falsetto the extreme membranous edges, i.e. the edges furthest away from the middle of the gap between the folds, appear to be the only parts vibrating. The mass corresponding to the innermost part of the thyro-arytenoid muscle remains still and motionless.

Some singers feel a sense of muscular relief when they change from the modal register to the falsetto register.

Research has revealed that not all speakers and singers produce falsetto in exactly the same way. Some speakers and singers leave the cartilaginous portion of the glottis open (sometimes called mutational chink), and only the front two-thirds of the vocal ligaments enter the vibration. The resulting sound, which is typical of many adolescents, may be pure and flutelike, but is usually soft and anemic in quality. In others, the full length of the glottis opens and closes in each cycle. In still others, a phenomenon known as damping appears, with the amount of glottal opening becoming less and less as the pitch rises, until only a tiny slit appears on the highest pitches. The mutational chink type of falsetto is considered inefficient and weak, but there is little information available about the relative strengths and weaknesses of the other two types

Female falsetto

The issue of the female falsetto voice has been met with some controversy, especially among vocal pedagogists. Many books on the art of singing completely ignore this issue, simply gloss over it, or insist that women do not have falsetto. This controversy, however, does not exist within the speech pathology community and arguments against the existence of female falsetto do not align with current physiological evidence. Motion picture and video studies of laryngeal action reveal that women can and do produce falsetto, and electromyographic studies by several leading speech pathologists and vocal pedagogists provide further confirmation.

One possible explanation for this failure to recognize the female falsetto is the fact that the difference in timbre and dynamic level between the modal and falsetto registers often is not as pronounced in female voices as it is in male voices. This is due in part to the difference in the length and mass of the vocal folds and to the difference in frequency ranges.It is an established fact that women have a falsetto register and that many young female singers substitute falsetto for the upper portion of the modal voice. Some vocal pedagogists believe that this failure to recognize the female falsetto voice has led to the misidentification of young contraltos and mezzo-sopranos as sopranos, as it is easier for these lower voice types to sing in the soprano tessitura using their falsetto register. Female singers of popular music noted for possessing a falsetto register are Leona Lewis, Christina Aguilera and Whitney Houston.

Use in singing

Falsetto is more limited in dynamic variation and tone quality than the modal voice. Falsetto does not connect to modal voice except at very low volumes, leading to vocal breaks when transitioning from modal voice. Most trained singers have at least an octave of range that they can sing in either modal voice or falsetto. In the absence of modern vocal training to hold back the volume of modal voice, in this overlapping area a given pitch in modal voice will be louder than the same pitch sung in falsetto. The type of vocal cord vibration that produces the falsetto voice precludes loud singing except in the highest tones of that register; it also limits the available tone colors because of the simplicity of its waveform. Modal voice is capable of producing much more complex waveforms and infinite varieties of tone color. Falsetto, however, does involve less physical effort by the singer than the modal voice and, when properly used, can make possible some desirable tonal effects.

The falsetto voice has a number of highly specialized uses within a musical context. The following list includes the most common ones:

·   in a male choir, to enable the first tenor to maintain the very demanding tessitura.

·   in yodeling

·   in Barbershop music for the Tenor voice (not always necessary) and occasionally with the Lead and Baritone voices in certain arrangements.

·   for comic effect in both operas and musicals

·   by some lyric (Irish) tenors, folk singers, and so forth

·   by falsettists or countertenors

·   for pitches which are above the range of the modal register

·   for pianissimo tones that would be difficult to execute in the modal register

·   for vocal development

Singing in falsetto is a vocal technique that produces sounds that are pitched higher than the singer's normal range. In boys or men, it can sound a little artificial. In females it sounds more 'normal'. It's other name is 'Head Voice', although some people refer to Head Voice as a stronger version of falsetto where the voice has been trained to withstand more air pressure underneath the vocal chords. The voice tone of falsetto has is breathy because the length of the vocal chords are not coming together properly, so air is escaping, much like a gas leak. It is not 'wrong' to sing in falsetto or even use it from time to time. In more and more popular music singing styles, artists are using falsetto to portray moments of tenderness, sexyness or vulnerubility. Some people, consider it a vocal weakness to flip over into falsetto while others consider it a vocal feature. It all depends on what you are trying to get the audience to feel. Falsetto singing is sometimes said to be the healing part of the voice. Males find falsetto a little harder to access than females and should not ignore this part of their voice training during singing lessons. During singing lessons falsetto should always be accessed by a singing teacher so as to give the student a more thourough voice training session.

One of the most common questions that we get at Singing Success is some version of this:
'Isn't 'head voice' the same as 'falsetto'?'
If you've ever wondered that, you'll want to read this 'vocal tips' issue.
Here's the short answer: Head voice and falsetto are not the same, but so many people (including MANY vocal teachers) think they are the same that the terms have become confused and are commonly used interchangably. BUT THEY SHOULDN'T BE.
I know that's a long 'short answer.' 

The easiest way to understand the difference of course is to simply HEAR examples of both. Clear head voice doesn't sound like falsetto.

But since I can't sing in this email to show you the difference, you'll need to go to Brett's free online lesson (which is an excerpt from his 'Brett Manning Live!' DVD) to hear with your own ears.

This issue will deal with what happens physically to make these two very different vocal sounds.

What's In A Name?

Falsetto means literally 'false voice.' To identify whether the sound you are making is falsetto or not, listen for a very 'airy' sound. If up high, your tone changes from firm and clear to airy, that's falsetto. 

The reason falsetto has an airy tone is because of how it's produced by the vocal cords. In falsetto, the tiny vocal folds are coming close enough to one another to cause the edges to vibrate as the air flows between them, but they are not making contact with one another.
The airy sound comes from all the air that escapes through the space left between the cords. 

**If you have Brett's program, in the workbook, you can actually see photos of Brett's vocal cords doing these different vocal coordinations.
You'll notice a tiny space between the cords when he's doing his falsetto voice. But with head voice something completely different happens.
To understand what Head Voice is, we first must look at another voice. 

"a coordination where the outer layer of the vocal cord (mucosa, i.e. internal skin or muscular covering) is vibrating, creating sound, but without engaging the actual musculature of the cord. Also, there exists no medial compression. In other words, during the vibratory cycle, the cords never fully approximate. In head voice, the cords approximate, but the vibration of the cord moves away from the full depth of the vocal cord (chest voice) to a pattern that involves less and less depth of vocal cord as you ascend toward the top of your range. The highest notes of your range involve only the vocal ligament. However, there is no consensus among experts on the official definition of vocal registers."

Source:

http://en.wikipedia.org/wiki/Falsetto

http://www.artspace2000.com/singing_lessons/singing_tips/falsetto.htm

http://www.singingfreedom.com/singing-lesson/falsetto-voice-training.php

http://www.become-a-singing-master.com/head-voice-and-falsetto.html

Vibrato

Vibrato is a musical effect consisting of a regular pulsating change of pitch. It is used to add expression to vocal and instrumental music. Vibrato is typically characterized in terms of two factors: the amount of pitch variation ("extent of vibrato") and speed with which the pitch is varied ("rate of vibrato").

It is with increasing frequency that singers write me and ask the question, "What is vibrato and how do I develop it in my voice?" Another question that arises is "Are there certain singers who just don't have that kind of sound in their vocal production? Can vibrato be developed?" I will try to address these questions and offer some thoughtful advice to those who wish to have vibrato defined. I will also give some concrete ideas on how to vocalize in such a way that vibrato is encouraged to develop.

I define vibrato as a "slight variation of pitch resulting from the free oscillation of the vocal cords". This free oscillation of the vocal cords results from
(a) an open pharynx or what many call the "open throat" along with
(b) healthy "closure of the cords" (see article on vocal cord closure) I consider that vibrato is a result of these two opposites working together: open throat and closed cords.
(c) Another major factor to be considered in regard to vibrato is the even sub-glottic breath pressure. This is regulated by the "support system" which involves the abdominal muscles, lower lumbar/upper gludial muscles, intercostal muscles and pectoral muscles. (See articles on breath and breath management).
Environmental Factor: As a child, I always had a vibrato. Whether developed through vocal freedom or imitation I do not know. I had an older sister who was an excellent soprano and used to sing a lot of opera and operetta in the home. I found great joy in imitating her vocal sound while I was still a boy soprano. I could match it quite well and was later asked to join the Texas Boy's Choir because I had a healthy and even vocal sound. Other cultures encourage different types of vibrato. For example, in some Asian cultures, a wide and slow vibrato is very desirable. Many French pop singers use a faster tighter vibrato. Neither of these examples represents healthy vocalism.

Vibrato Problems:
(1) The Vocal Wobble:
We often hear singers that have a wide and slow vibrato (see article on the vocal wobble.) The causes have been described in the article entitled "The Vocal Wobble". A wide vibrato is usually a lack of proper "resistance of the breath pressure" or a lack of "focus in the tone". It can also be a result of a lack of proper adduction of the vocal cords. One or all of these problems create a sound that our culture defines as "age in the voice". I have found that singers in their 20's can have a wobble. I have students in my studio who are in their 70's who have no sign of such a vocal characteristic. In fact, they have what our culture calls a youthful, and more importantly, healthy sound. I have found the primary cause of the vocal wobble to be misuse rather than age. An unhealthy vocal technique used over a short or long period of time can be the cause such a vocal problem. The solution is quite simple: vocalize exercises that require body support along with focus. The "ng" is a healthy sound that can help develop focus in the voice. The sustained "hiss" can help a singer learn what muscles to use in order to "hold back" the breath pressure or "support the tone".

(2) The Overly-Fast Vibrato:
Some singers have an overly fast vibrato that can be as disconcerting as the wobble. Neither the wobble nor the fast-vibrato is the desired vocal sound for healthy singing. A fast-vibrato can be caused by a number of vocal situations.
(a) Pressure at the root of the tongue. This pressure at the root of the tongue can have its origin at inhalation or at the attack or onset of sound.
(b) Lack of vocal cord approximation: Many singers who do not quite understand that the vocal cords must close after inhalation. This lack of proper adduction of the cords can result in a faster vibrato speed. If the vocal cords do not approximate closely enough, the vibrato can become faster depending upon the size and shape of the vocal cords themselves.
(c) Lack of support is another cause of this vocal problem. Most of us have heard singers with definite vibrato problems and we have experienced singers with healthy vibrato. One key factor in attaining a healthy sound is to be sure that the vibrato is vibrating at an even rate. An uneven vibrato can be caused by sudden changes in the sub-glottic breath pressure. This is caused by a lack of even "body resistance" or support in the body. The vocal cords then begin to separate and vibrate unhealthily. The result is an uneven vibrato sometimes accompanied by pitch problems. The fast vibrato is less noticeable if the rate of vibrato is even rather than sporadic.

(3) The Straight Tone:
So often I have singers who come into my studio with a straight tone (no vibrato). Some of these singers are not aware of vibrato or how it is developed in the voice. Many come into my studio with the express desire to develop vibrato in their sound realizing that their voice is lacking in that particular area. In over 25 years of teaching, I have never had a singer in my studio that could not develop healthy vibrato.
Some straight tone singers have sung in choirs where the director has demanded straight tone. This is potentially a damaging circumstance. Straight tone singing is extremely unhealthy for the voice. Vocal nodules can result from such vocal production because of too much pressure held at the glottis to prevent vibrato from occurring in the tone. Choral blend is developed through vowel and acoustical alignment, not squeezing the voice into straight tone sound. The proper vowel and acoustical alignment can create a beautiful vocal blend. I experienced this personally in Berlin when 11 of my singers sang "Let Your Garden Grow" from Candide as a finale along with a men's choir. The resulting vocal sound of these 11 singers who were trained on the "ng" ring was amazing to say the least. Because these singers were trained with vowel and resonance alignment, the resulting sound was one of beautiful blend of tone along with fullness of vocal sound and blend. Several conductors from German opera houses came to me after the concert to ask about the training of these singers.
Most straight tone singers cannot use the idea of vocal cord closure during the first part of their training because "too much pressure" has been held at the vocal cords for too long a time period. I have found that vibrato comes into the voice when the singer achieves proper balance in the "support muscles" and when the singer keeps the feeling of the "u" vowel in the pharynx. The Italian "u" is a crucial part of a singer's training in order for vibrato to occur. The "u" vowel allows a healthy adduction of the vocal cords without too much pressure at the glottis. It is understandable that this vowel is crucial in the Italian School. I find that the "u" vowel must be produced without the "bunching" of the back of the tongue and with a "high and wide soft palate" in order to be efficient acoustically. The result is beauty and resonance simultaneously. 

(4) Diaphragmatic Vibrato:
A diaphragmatic vibrato is the pulsating of the diaphragm during a sustained tone to "create" a false vibrato. Music theatre singers develop this damaging vocal habit in order to have some sort of vibrato when none is present in the tone. This is a huge mistake. A diaphragmatic vibrato is difficult to repair because the lower abdominal muscles memorize the pulsating sensation so deeply. This situation can be repaired with lots of time and hard work. Solution: Use the idea of the sustained "hiss" and memorize what the body "feels" during this function. Then sing a tone while keeping the same "feel" in the body. This will stabilize the shaking diaphragm.

(5) The role of the vocal trill:
In some cases, a singer can begin to awaken the vibrato function by using a trill. A trill is an educated yodel at the vocal cords that may or may not be easy for a singer to produce. Some connect with this idea and begin to release the "over-squeezing" of the vocal cords, therefore allowing for the development of a vibrato.
Healthy vibrato can be achieved in a rather short period of time. Usually the time factor is dependent upon the singer's mind/body coordination. Some singers have more of a connection to their body than others. I recently had a large-voiced baritone who began to develop some vibrato in his sound after only three lessons. I have had others who have taken much longer because of singing straight tone for so many years. At any rate, any singer can achieve a properly regulated and even vibrato with concentration, proper instruction, and by embracing the process rather than the result. Patience is a most important aspect while training and balancing vocal production.
The use of vibrato is intended to add warmth to a note. In the case of many string instruments the sound emitted is strongly directional, particularly at high frequencies, and the slight variations in pitch typical of vibrato playing can cause large changes in the directional patterns of the radiated sound. This can add a shimmer to the sound; with a well-made instrument it may also help a solo player to be heard more clearly when playing with a large orchestra

Typical rate and extent of vibrato
The rate and extent of the variation in pitch during vibrato is controlled by the performer. The extent of vibrato for solo singers is usually less than a semitone (100 cents) either side of the note, while singers in a choir typically use narrower vibrato with an extent of less than +/- a tenth of a semitone (+/- 10 cents). Wind and bowed instruments generally use vibratos with an extent of less than +/- half a semitone

Vibrato's use in various musical genres
Vibrato is sometimes thought of as an effect added onto the note itself, but in some cases it is so fully a part of the style of the music that it can be very difficult for some performers to play without it. The jazz tenor sax player Coleman Hawkins found he had this difficulty when requested to play a passage both with and without vibrato by the producer of a children's jazz album to demonstrate the difference between the two. Despite his technique, he was unable to play without vibrato. A symphony saxophonist was brought in to play the part.
Many classical musicians, especially singers and string players, have a similar problem. The violinist and teacher Leopold Auer, writing in his book Violin Playing as I Teach It (1920), advised violinists to practise playing completely without vibrato, and to stop playing for a few minutes as soon as they noticed themselves playing with vibrato in order for them to gain complete control over their technique.

In classical music
The use of vibrato in classical music is a matter of some dispute. For much of the 20th century it was used almost continuously in the performance of pieces from all eras from the Baroque onwards, especially by singers and string players. A drastic change in approach cannot be understood wholly without regarding the rise of notionally historically accurate ("period") performance from the 1970s onwards. However, there is no actual proof that singers performed without vibrato in the baroque era. Vocal music of the renaissance is almost never sung with vibrato as a rule, and it seems unlikely it ever was. There are only a few texts from the period on vocal production, but they all condemn the too frequent use of vibrato. However, it should be understood that "vibrato" occurs over a wide range of intensities: slow, fast, wide, and narrow. Most sources in condemning the practice seem to be referring to a wide, slow, perceptible oscillation in pitch, usually associated with intense emotion, whereas the ideal for modern vibrato, and possibly in earlier times as well, was to imitate the natural timbre of the adult singing voice, from which a measure of vibrato (it has since been shown) is rarely absent.

Leopold Mozart’s Versuch einer gründlichen Violinschule (1756), for example, provides an indication of the state of vibrato in string playing at the end of the baroque period. In it, he concedes that “there are performers who tremble consistently on each note as if they had the permanent fever”, condemning the practice, and suggesting instead that vibrato should be used only on sustained notes and at the ends of phrases when used as an ornament. This however, does not give anything more than an indication of Mozart's own personal taste, based on the fact that he was an educated late Rococo/Classical composer. Mozart acknowledges the difference between the heavy, ornamental vibrato that he finds objectionable, and a more continuous application of the technique less obtrusively for purposes of improving tone quality (in which case he does not refer to it as "vibrato" or "tremolo" at all; describing it merely an aspect of correct fingering). In this respect he resembles his contemporary, Francesco Geminiani, who advocated using vibrato "as frequently as possible" on short notes for this purpose. Although there is no aural proof, as audio recordings were not around for more than 150 years, that string players in Europe did not use vibrato, its overuse was almost universally condemned by the leading musical authorities of the day.

Certain typtes of vibrato, then, were seen as an ornament, but this does not mean that it was used sparingly. In wind playing too, it seems that vibrato in music up to the 20th century was seen as an ornament to be used selectively. Martin Agricola writing in his Musica instrumentalis deudch (1529) writes of vibrato in this way. Occasionally, composers up to the baroque period indicated vibrato with a wavy line in the sheet music. Again, this does not suggest that it was not desired for the rest of the piece any more than the infrequent use of the term in 20th century works suggests that it is not used elsewhere.

Vibrato wars
Music by late Romantic composers such as Richard Wagner and Johannes Brahms is now played with a fairly continuous vibrato. However, some musicians specialising in historically informed performances such as the conductor Roger Norrington argue that it is unlikely that Brahms, Wagner, and their contemporaries would have expected it to be played in this way. This view has caused considerable controversy. The view that continuous vibrato was invented by Fritz Kreisle and some of his colleagues is held to be shown by early sound recordings, which allegedly demonstrate that vibrato appeared only in the 20th century. Against this are cited sources which are said to prove that early 19th-century Viennese string players like Franz Clement and Joseph Mayseder were noted for their tasteful use of vibrato. These musicians (and the two Hellmesbergers) are said to represent the school on which Fritz Kreisler based his stylistic approach.

The alleged growth of vibrato in 20th century orchestral playing has been traced by Norrington by studying early audio recordings but his opponents contend that his interpretations are not supported by the actual samples. Norrington claims that vibrato in the earliest recordings is used only selectively, as an expressive device; the Berlin Philharmonic Orchestra were not recorded using vibrato comparable to modern vibrato until 1935, and the Vienna Philharmonic Orchestra not until 1940. French orchestras seem to have played with continuous vibrato somewhat earlier, from the 1920s.

Defenders of vibrato claim that the sonic limitations of 78-rpm recordings, particularly with respect to overtones and high frequency information, make an uncontroversial assessment of earlier playing techniques difficult (although, it must be said, early recordings of operatic singers manage to show clearly the extent to which a vibrato is present [or not] in their voices). In addition, the defenders of vibrato point out a distinction needs to be made between the kind of vibrato used by a solo player, and the sectional vibrato of an entire string ensemble, which cannot be heard as a uniform quantity as such. Rather, it manifests itself in terms of the warmth and amplitude of the sound produced, as opposed to a perceptible wavering of pitch. The fact that as early as the 1880s composers such as Richard Strauss (in his tone poems "Don Juan" and "Death and Transfiguration") as well as Camille Saint-Saëns (Symphony No. 3 "Organ") asked string players to perform certain passages "without expression" or "without nuance" strongly suggests the general use of vibrato within the orchestra as a matter of course.
Despite this, the use of vibrato in late Romantic music is still common, though challenged by Roger Norrington and others of the historically informed performance movement. Performances of composers from Beethoven to Arnold Schoenberg with limited vibrato are now not uncommon. Norrington caused controversy during the 2008 Proms season by conducting Edward Elgar's Enigma Variations, and the Last Night of the Proms, in non-vibrato style, which he calls pure tone. Some take the view that even though it may not be what the composer envisioned, vibrato adds an emotional depth which improves the sound of the music. Others feel that the leaner sound of vibratoless playing is preferable. In 20th century classical music, written at a time when the use of vibrato was widespread, there is sometimes a specific instruction not to use it (in some of the string quartets of Béla Bartók for example). Furthermore, some modern classical composers, especially minimalist composers, are against the use of vibrato at all times.

In opera
All human voices possess the capacity to produce a vibrato. This vibrato can be varied in width (and rapidity) through training. In opera, as opposed to pop, vibrato begins at the start of the note and continues to the end of the note with slight variations in width during the note.
Traditionally, however, the deliberate cultivation of a particularly wide, pervasive vibrato by opera singers from the Latin countries has been denounced by English-speaking music critics and pedagogues as a technical fault and a stylistic blot (see Scott, cited below, Volume 1, pp. 123–127). They have expected vocalists to emit a pure, steady stream of clear sound — irrespective of whether they were singing in church, on the concert platform, or on the operatic stage.

During the 19th century, for instance, New York and London based critics, including Henry Chorley, Herman Klein, and George Bernard Shaw, castigated a succession of visiting Mediterranean tenors for resorting to an excessive, constantly pulsating vibrato during their performances. Shaw called the worst offenders "goat bleaters" in his book Music in London 1890-1894 (Constable, London, 1932). Among those censured for this failing were such celebrated figures as Enrico Tamberlik, Julián Gayarre, Roberto Stagno, Italo Campanini and Ernesto Nicolini—not to mention Fernando Valero and Fernando De Lucia, whose tremulous tones are preserved on the 78-rpm discs that they made at the beginning of the 20th century.

The popularity of an exaggerated vibrato among many (but by no means all) Mediterranean tenors and singing teachers of this era has been traced back by musicologists to the influential example set by the early-19th century virtuoso vocalist Giovanni Battista Rubini (1794–1854). Rubini had employed it with great success as an affecting device in the new Romantic operas of Gaetano Donizetti and Vincenzo Bellini. A host of young Italian tenors—including the renowned Giovanni Mario (1810–1883) — copied Rubini's trend-setting innovation in order to heighten the emotional impact of the music that they were singing, and to facilitate the delivery of fioritura "by, as it were, running up and down the vibrato" (to quote Scott; see p. 126).

Prior to the advent of the charismatic Rubini, every well-schooled opera singer had avoided using a conspicuous and continuous vibrato because, according to Scott, it varied the pitch of the note being sung to an unacceptable degree and it was considered to be an artificial contrivance arising from inadequate breath control. British and North American press commentators and singing teachers continued to subscribe to this view long after Rubini had come and gone.

Accordingly, when Enrico Caruso (1873–1921) — the most emulated Mediterranean tenor of the 20th century — made his acclaimed New York Metropolitan Opera debut in November 1903, one of the specific vocal attributes for which he was praised by music reviewers was the absence of a disruptive vibrato from his singing. The scholarly critic William James Henderson wrote in The Sun newspaper, for example, that Caruso "has a pure tenor voice and [it] is without the typical Italian bleat". Caruso's gramophone recordings support Henderson's assessment. (Other prominent Mediterranean tenors of the late 19th century-early 20th century who, like Caruso, did not "bleat" were Angelo Masini, Francesco Tamagno, Francesco Marconi, Francisco Viñas, Emilio De Marchi, Giuseppe Borgatti and Giovanni Zenatello, while the phenomenon was rare among French, German, Russian and Anglo-Saxon tenors of the same period—see Scott.)

The intentional use of a pronounced vibrato by Mediterranean tenors is a practice that has died out over the course of the past 100 years, owing in no small measure to Caruso's example. The last really important practitioners of this style and method of singing were Alessandro Bonci (in the 1900-1925 period) and Giacomo Lauri-Volpi (in the 1920-1950 period). Both of them featured bel canto works, dating from Rubini's day, in their operatic repertoires, and both of them can be heard on recordings which faithfully capture the distinct shimmer inherent in their timbre.

Italian or Spanish-trained operatic sopranos, mezzo-sopranos, and baritones exhibiting a pronounced vibrato did not escape censure, either, by British and North American arbiters of good singing. Indeed, Adelina Patti and Luisa Tetrazzini were the only Italian sopranos to enjoy star status in London and New York in the late-Victorian and Edwardian eras, while such well-known compatriots and coevals of theirs as Gemma Bellincioni and Eugenia Burzio (among several others) failed to please Anglo-Saxon ears because, unlike Patti and Tetrazzini, they possessed unsteady, vibrato-laden voices—see Scott for evaluations of their respective techniques. To give an additional female example from a later date, whenever the vivacious mezzo-soprano of the 1920s and '30s, Conchita Supervia, performed in London, she was admonished in print for her exceedingly vibrant and fluttery tone, which was unkindly likened by her detractors to the chatter of a machine-gun or the rattle of dice in a cup.

In 1883, Giuseppe Kaschmann (né Josip Kašman) — a principal baritone at La Scala, Milan—was criticised for his strong vibrato when he sang at the Met, and the theatre's management did not re-engage him for the following season, even though other aspects of his singing were admired. (Kaschmann never performed in Great Britain but he remained a popular artist in the Latin countries for several decades; in 1903, he made a few recordings which exhibit only too well his perpetual flutter.) Similarly, another one of Italy's leading baritones, Riccardo Stracciari, was unable to turn his pre-World War I London and New York operatic engagements into unambiguous triumphs due to an intrusive quiver in his tone. He subsequently moderated his vibrato, as the discs that he made for Columbia Records in 1917-1925 show, and this enabled him to pursue a significant career not only in his homeland but also at the Chicago opera.

There is another kind of vibrato-linked fault that can afflict the voices of operatic artists, especially ageing ones—namely the slow, often irregular wobble produced when the singer's vibrato has loosened from the effects of forcing, over-parting, or the sheer wear and tear on the body caused by the stresses of a long stage career.

Techniques for producing vibrato
Not all instruments can produce vibrato, as some have fixed pitches which cannot be varied by sufficiently small degrees. Most percussion instruments are examples of this, for instance the xylophone.

Keyboard instruments
Some types of organ however, can produce the effect by altering the pressure of the air passing through the pipes, or by various mechanical devices (see the Hammond or Wurlitzer Organs for example). The clavichord, though technically a fixed-pitch keyboard instrument, is capable of producing a type of vibrato known as Bebung by varying the pressure on the key as the note sounds. Some digital keyboards can produce an electronic vibrato effect, either by pressure on the keys, or by using a joystick or other MIDI controller

String instruments
The method of producing vibrato on other instruments varies. On string instruments, for example, the finger used to stop the string can be wobbled on the fingerboard, or actually moved up and down the string for a wider vibrato.
Many contemporary string players vary the pitch from below, only up to the nominal note and not above it, although great violin pedagogues of the past such as Carl Flesch and Joseph Joachim explicitly referred to vibrato as a movement towards the bridge, meaning upwards in pitch, and the cellist Diran Alexanian, in his 1922 treatise Traité théorique et pratique du Violoncelle, shows how one should practice vibrato as starting from the note and then moving upwards in a rhythmic motion. In a 1996 acoustic study by the Acoustical Society of America, along with Wellesley College and the Massachusetts Institute of Technology, found that the perceived pitch of a note with vibrato "is that of its mean", or the middle of the fluctuating pitch.

The guqin, a Chinese bridgeless zither, has documents describing over 25 different types of vibrato that can be executed. Most peculiar is the vibrato ting yin (literally "still vibrato"); ancient manuals state that the finger on the left hand that is pressing the string should only move or rock ever so slightly so as to alter the pitch minutely, and some manuals say that the finger should not move at all but let the pulse of the finger do the vibrato.

Wide vibrato, as wide as a whole-tone, is commonly used among electric guitar players and adds a vocal-like expressiveness to the sound. This effect can be achieved both by the movement of fingers on the fretboard and by the use of a tremolo arm, a lever that adjusts the tension of the strings.

Wind instruments
Players of wind instruments generally create vibrato by modulating their air flow into the instrument. This may be accomplished either through stomach vibrato, the pulsing of the diaphragm slightly up and down, or throat vibrato, a variation of vocal chord tension to manipulate air pressure as singers do. Players of other instruments may employ less common techniques. Saxophonists tend to create vibrato by repeatedly moving their jaw up and down slightly. Clarinet players rarely play with vibrato, but if they do, the saxophone method is common because of the similarity of the saxophone and clarinet mouthpieces and reeds.

Brasses
Brass instrument players may produce vibrato by gently shaking the horn which varies the pressure of the mouthpiece against the lip. Alternatively, the embouchure can be rapidly altered, essentially repeatedly "bending" the note. On a trombone, a player may provide a slightly more pronounced vibrato by gently moving the slide back and forth, centering on one note to give a lyrical effect.

Auto-vibrato
Some instruments can only be played with constant, mechanical vibrato (or none at all), notably electric organists using a Leslie speaker. Vibrato on the theremin, which is a continuously variable-pitch instrument with no "stops", can range from delicate to extravagant, and often serves to mask the small pitch adjustments that instrument requires

David Bowie has a fast one. Mary J. Blige has a slow, sultry, one. Maynard James Keenan doesn’t have a trace of one. Singing with vibrato is a matter of taste. Having a choice is a matter of control. For most singers, the subtle, rhythmical movement of vibrato feels more like fate. When you want vibrato, it hides on you; don’t think about it, and it shimmers on the end of a note. Vibrato brings vitality to a voice. Sound without variation is boring. Compare a refrigerator to a fly buzzing around. The steady hum of the compressor quickly becomes background noise while the bug gets harder to ignore. With the exception of rappers and singers like Beck who don’t sustain notes, those without vibrato tend to rely on overdrive to create excitement. This often leads to blow outs. The more vocal colors available on your pallet, like vibrato, breathy, nasal and gritty, the easier it will be to paint an interesting portrait of a song without killing yourself.

The mechanics of vibrato are simple and reflexive, which is what makes it so elusive. Picture the fret hand of a guitarist sustaining a note. The finger movement alters the length of the string creating a slight waver in pitch. Things are just a little more complex with the voice. Like a stringed instrument, the tension of the vocal folds is varied rhythmically, creating movement in pitch. Along with this tension change, though, is a variation in the thickness of the vocal fold. The combined movements of pitch, volume and tone are what set vibrato apart from tremolo (change in volume only) and wobble (change in pitch only).

Tension squashes vibrato. Not just the obvious neck bulging stuff, but subtle everyday stiffness can neutralize it as well. Like the freedom required to wiggle your finger when sustaining a note on guitar, vocal vibrato requires muscle independence. Backing off the air pressure is the first step to releasing your voice. Let the ability to produce vibrato be your guide. Lay down flat on your back and place your hand on your belly button. Breath so that your hand rises and falls. Now sing a comfortable note and look for the presence of vibrato. If the pitch is stiff notice what your abs are doing. Are they contracting to drive the note? Check the behavior on various pitches. If you push too much from your stomach, the muscles surrounding the larynx will brace and vibrato will be lost. Reduce the volume and try again. The goal is to reduce the air pressure to the point where flexibility is found. Don’t be alarmed if this only happens at very low volumes. With practice, you’ll be able to increase the volume without loading the neck with pressure. Strike the proper balance during a song and vibrato will blossom. That’s why it tends to come in at the ends of notes; once we feel safely on pitch, we ease off the pressure a bit. 

Another check for vibrato-eating throat tension is to rotate your head in a small circle when singing. Pretend you are tracing the outline of a quarter with your nose. Does the rotation stop when you begin to sing? Is it stiffer on high notes? Again, reduce the volume until you find the correct air pressure. Neck tension is not a requirement of singing loud or high. We often see singers so locked up in the neck that they literally have to shake their heads or jaws in order to create vibrato. In the same way, a guitar player who needs to shake the guitar to move a note must be applying a death grip on that fretboard. There’s nothing wrong with using force to make a strong statement. Too often, though, the statement it makes is that we are overcompensating to mask weakness. Be brave and do the dirty work in private. Use vibrato as your guide and discover the power within. 

How To Develop An Outstanding Singing Vibrato
You see, when vibrato is flowing effortlessly in your voice it means that something good is happening. Vibrato is a sign of good vocal technique. Plus it sounds fantastic. he chances are that once you master your singing vibrato, you will be able to connect with all areas of your voice, low and high. And your voice will most likely sound very balanced as well.
So where does vibrato come from, and how can you develop an effortless one? Let's explore this further. Vibrato happens when your voice shifts quickly between two pitches. So if you were to sing a middle C, and then a C# and then a C again, followed by a C# followed by a C, you would be singing with vibrato. The key to a great vibrato is the speed in which you change between the two pitches. If you can oscillate between the two pitches around six times per second, you will have a very natural sounding vibrato. 

Let's Do An Exercise To Get Your Singing Vibrato Happening!
Here is a simple exercise that will allow you to see what singing vibrato feels like. Please understand that this is not a finished sound. It's an exaggerated version that will later be honed into something more usable. 

Here's how to do the exercise.
1. Place your hands at the bottom of your chest and feel where your ribs come together in the middle. Now move your hands slightly below this point. (it's the soft area a few centimeters above your belly button)
2. Now sing a note on one pitch in your easy range. Any note will do.
3. As you're singing this note, push in gently with your hands. The key is to push in, then pull out, and push in, then pull out and so on. Try doing this at a rate of around 3 to 4 cycles a second. 

Listen to how your voice wavers in a singing vibrato like fashion. Now it probably sounds a little exaggerated at this point, but this exercise is just to get things going. There is a home study course that includes many highly effective exercises that will help you develop an amazing vibrato. You will also learn how to increase your vocal range, improve your tone quality, and gain greater control over your voice.


Source :
http://en.wikipedia.org/wiki/Vibrato
http://www.voiceteacher.com/vibrato.html
http://www.voicelesson.com/html/lessons/free_lessons_07.htm
http://www.become-a-singing-master.com/singing-vibrato.html