How To Improve Your Vibrato
In 1756, Leopold Mozart described vibrato in his book, Versuch einer gründlichen Violinschule, saying, "The left-hand finger should make a small, slow movement, which, however, must not go toward the side, but forward and backward. That is, the finger should bend forwards towards the bridge and backwards towards the violin’s scroll, quite slowly for soft tones, but somewhat faster for loud ones."
This vibrato technique, often described as an ornament, creates a wavering of tones for extended notes that become an inherent part of the composition's emotional expression. When done well, the effect is an appealing enhancement; when too rigid, abrupt or overused, vibrato becomes a nuisance. That's why intermediate string musicians are wise to improve and perfect their vibrato technique, with the same level of diligence used to enrich their instrument's sound when they were beginners.
There are plenty of techniques used for teaching vibrato, but there are also some tips musicians can adopt on their own to make their vibrato honey-toned and palatable, as opposed to harsh and used to excess.
Make the Starting Note as Beautiful as Possible
Since the finger motion used to produce vibrato wavers the pitch of the note in small increments, it's essential that the starting note be pitch-perfect and have a rich, lovely tone to begin with. Otherwise, the vibrato is un-anchored, and the wavering pitch used to convey emotion becomes a detriment to the overall sound effect.
Anchoring from a beautiful starting note (pitch) requires good intonation and an adept knowledge of the fingerboard. If you're still getting these basics down, don't leap ahead. Your determination to play the vibrato will impede the ability to create the root of accurate pitch required to do it well. If you don't have those fundamentals in place, be patient and know your patience will be rewarded down the road when you produce beautiful sounds - with or without vibrato.
Align the Base of the Knuckles Parallel with the Strings
When your left-hand is in place (particularly in the lower positions), verify that the base of the knuckles run parallel with the strings. If they aren't parallel, the rocking of the finger back and forth is more difficult and strained, the fourth finger becomes restricted, and the motion is wasted.
Think of Your Joints as Being Loose & Springy
There is a false assumption for players learning to play vibrato that you need to clamp down harder to grip the neck and fingerboard and rock the vibrato finger more securely. In fact, as with playing in general, it's important that your body and joints are loose and relaxed so that your playing remains fluid. This fluidity will show up in better sound quality, and you'll feel the difference in your body.
While practicing vibrato, have your teacher or a trusted musician friend tug lightly on your left elbow in the hopes that it automatically "springs" back into place as if it is floating in a pool of water. Similarly, your thumb should not press against the neck but should rest lightly against it. Any tension in your body will show up in the vibrato (abrupt and sharp, rather than languid and expressive).
We recommend viewing this video from Violin Lab, where you can watch vibratos on all four of the fingers, played in real time and slow motion. You'll be amazed at how relaxed the finger is as it moves back and forth, rocking on the firmly anchored pad. This is very difficult to observe via your own fingers when they're in motion, so this video provides a unique opportunity to view flexible, relaxed vibratos from multiple vantage points.
Keep the Pitch as the Top Boundary; It's all Down (hill) From There
The human ear is inherently programmed to perceive the highest pitch (there's rarely more than a single piccolo playing in the orchestra...). Thus, if you start on the pitch - in tune - and vibrate upwards, the pitch sounds sharp. The appropriate method for creating a pleasing vibrato is to begin on the pitch and vibrate downwards instead, yielding a more appealing and sensual tone.
If you're just starting to work on the vibrato, be diligent about using a downward-first motion. If you've already begun learning to create vibrato with upwards-motion first, it can be a difficult habit to break. However, it's worth devoting your time to correcting as your current instructor (or one down the road) will eventually notice and it will be more difficult to correct over time.
Getting your teacher's "go ahead" to begin learning to play vibrato is one of the most exciting milestones in an intermediate string player's life. The ability to play vibrato well, in an intentionally controlled and proficient way, will take your musicianship to the next level, bringing new levels of depth to everything you play.
Above image of Joshua Bell courtesy of http://info.music.indiana.edu