This is fairly technical post, but several people have asked for ways to work on vibrato, so here goes.
The vibrato is created by a very tiny, regular pulsating change in pitch. It is such a small variation that the ear does not hear it as an actual pitch change but rather as a “waver” or “shake” within the tone. Singers do not normally think of creating vibrato because it occurs naturally when the voice is functioning at its best, when the flow of air and the way the vocal cords are vibrating together is optimal.
When there is no vibrato in the voice, the sound produced is referred to as a straight tone. When the voice is producing a straight tone, it is almost always because something in the vocal mechanism or body is tense. Various approaches to singing have ideals and exercises for relaxing as well as for developing posture, pacing the breath, bringing the vocal cords together and accessing resonance. If you have worked on all of these elements and still the tone is straight, there are some techniques and exercises that sometimes help to liberate the voice into a vibrant tone.
1. A single note vowel chant alternating between “EE” and “OOH”
The lips must form the smallest possible “OOH,” as though they are closing around a small drinking straw.
2. A scale passage that starts low and ascends in pitch on an “AH” vowel, then switches to a very small “OOH” vowel before singing the highest note and descending back to the original pitch.
3. A scale passage that starts low and ascends in pitch on an [λ] vowel, then switches to an “AH” vowel to sing the highest note and descend back to the original pitch.
A healthy, natural vibrato is between 5 to 7 cycles per second, depending on the size and character of the voice.
If the vibrato is present but too slow and broad, it can be helpful to work from a straight tone. Gradually release from the straight tone to produce only a tiny pulse in the tone. Once this is mastered release only enough more to produce a free, spinning vibrato. Because the pitch fluctuation is smaller, the vibrato will be faster.
A slow vibrato can also sometimes be corrected by playing with a tongue trill. Try sustaining a rolled “R” and notice the speed of the resulting trill. Next, sustain a note and intend for the vibrato to fluctuate at the same rate as the tongue trill. The vibrato will be slower than the tongue trill, but trying to match the speed of the tongue trill helps the body adjust and create a faster vibrato. If you have difficulty with a tongue trill, try a lip trill (which is produced by blowing air through slightly pursed lips and causing them to vibrate). This time try to match the rate of the vibrato on a sustained note to the speed of the fluctuation of the lips as they trill. Again, the vibrato will be slower but the physical analogy helps the body.
A full trill between two adjacent pitches can be used to broaden an excessively rapid, tight or narrow vibrato. Alternating between a full trill and a sustained note can help to reflex a fuller, richer vibrato.