Vibrato is used to add flavor and emotion to just about anything from a slow waltz to a classical caprice. The concept behind vibrato is that you are taking one note and pivioting your wrist, arm, and hand to lower and raise the pitch. Vibrato is a technique of the left hand and arm in which the pitch of a note varies in a pulsating rhythm. While various parts of the hand or arm may be involved in the motion, the end result is a movement of the fingertip bringing about a slight change in vibrating string length. Violinists oscillate backwards, or lower in pitch from the actual note when using vibrato, since perception favors the highest pitch in a varying sound.Vibrato does little, if anything, to disguise an out-of-tune note: in other words, vibrato is a poor substitute for good intonation. Still, scales and other exercises meant to work on intonation are typically played without vibrato to make the work easier and more effective.
Another factor in producin vibrato is learning about your points of contact with your left hand. When you are playing your left hand has 3 points of contact with the violin: The thumb, the 1st finger knuckle on the right side of the nut, and what ever finger you have pressed on the string.
Know take your 3rd finger and place it on the “A” string which produces a “D” note. Move the 2nd point of contact, the 1st finger knuckle, off the violin and make a back and forward motion with you arm, hand, and wrist, but keep your 3rd finger where it is located. The movement of you arm, hand, and wrist will force the 3rd finger to pivot and slightly change the pitch of the note producing a vibrato.
This techinque can then be prefected by playing with a metronome, or by playing with a rythym guitar, or piano.