A definition of vibrato is, ‘a musical effect consisting of a regular, pulsating change of pitch’.
In barbershop singing, we are constantly attempting to achieve chords that are locked and ring with the ideal result of producing expanded sound. That is where the overtones being produced by one section of singers reinforce the overtones being produced by the other sections, thus producing additional audible notes or expanded sound.
Now since these overtones are only produced when notes are being perfectly tuned, it becomes evident that the movement in and out of tune that vibrato creates is not compatible with the production of expanded sound.
The use of vibrato when attempting to produce the barbershop sound has therefore to be strongly discouraged.
Unfortunately with age, vibrato can and does creep in to the voice due to the weakening of the muscles used in the production of our notes. A contributing factor is also a reduction in the breath support used whilst singing. It is a fact that to produce a perfectly pure I.e non vibrato sound, takes much more effort than to produce one with vibrato. It has been said for instance, that opera singers would not be capable of singing the length of time they are required to sing in many of there classical pieces, if they were forced to sing only in pure tones.
For barbershop singing then, the question is, how can we minimise this age related tendency to produce this unintentional vibrato.
Well firstly, as mentioned above, we can spend more time developing our breath control. By this I mean ensuring that each breath we take is taken in a manner that fills the lungs from the bottom upwards which can only happen once the diaphragm has been lowered. Then, maintaining a constant support for your sound by using the diaphragm.
Exercises such as the one we have used many times in the past of breathing in then hissing out with the feeling of pressure.
Exercises whereby long notes are sung whilst remaining constantly aware that NO vibrato is produced.
Recording oneself and listening carefully to see if any vibrato is being produced. It is not always easy to recognise ones shortcomings whilst in performance mode and recognising one has a problem is an essential precursor to solving it.
Other things that can help would be ensuring that whilst singing you always do so from a correct stance. Any kinks in ones vocal tract will produce added strain to the sound production mechanism.
Maintaining a healthy life-style with less booze and more water. An American coach whose name escapes me used to say “drink right and pee white”
Avoid working your vocal mechanism too much by avoiding gang singing whenever possible.
When performing, try to ensure that you are as confident as possible with what you are about to do. Know your notes and words and sing with guys with whom you have confidence, because any nervousness you are feeling is likely to be reflected in the sound you produce.
Finally a word in support of vibrato. Not all instances of vibrato are unwelcome, even in barbershop singing. Vibrato can add colour to a note and where say, a lead or indeed a harmony singer has a solo spot, the use of a touch of vibrato at the ends of phrases can add a positive improvement to the sound. However I believe it can only apply to true instances of solo singing and is therefore most likely to be restricted to quartet performances.