Vibrato....a definition: A vibrato is the slight fluctuation of a note used by performers to intensify or prevent the note from sounding flat or stale. The vibrato is usually produced by rocking the hand back and forth while the finger is pressing down the note...this rocking motion sounds most natural if coming from the wrist instead of the entire arm. A vibrato can be achieved by different players in many different ways...each contributing to its own stylistic sound. Most commonly, the violin vibrato is achieved by rocking the hand from the wrist. Be careful not to develop any bad habits in your attempts to learn proper vibrato technique.

On a tremolo, the bow is rapidly drawn back and forth in short succession...this gives the effect of a rapid shuffle bow only sped up. This is relatively easily accomplished and only requires a fluid movement. The tremolo is a quick reiteration of the same note; this technique would be mostly used during a dramatic portion of an orchestral piece.

Since the term "tremolo" is commonly used in place of "vibrato", Many people may be referring to the vibrato effect which is where the left hand, the hand that plays notes on the fingerboard, is moved rapidly back and forth to accomplish a warbling sound on a drawn out note. This ensures that a long drawn out note doesn't sound flat. Singers use this effect so that notes do not sound flat when drawn out for any length of time.

On a violin, the vibrato can be one of the most difficult techniques to learn to do well. A minute fluctuation of pitch is accomplished by moving the hand back and forth as the note is being played. The vibrato technique also serves the violinist well if the intonation is slightly off...when you arrive at the note, and it turns out to be slightly flat or sharp, simply add a strong vibrato and it will appear true in pitch. Traditionally, violin masters felt that the vibrato should be used sparingly and only during heightened levels of note expression. Today, I hear the vibrato used most often both in fiddling and in violin technique. Any time I draw out a note, I'll add just a little vibrato so that the note does not become blase...I'm also careful not to exaggerate the vibrato. I personally believe it should only be added as a tasteful highlight..not as an end in itself.

How do you accomplish a vibrato? With lots of focus and practice. It's next to impossible to learn vibrato technique from the written word.

What to avoid when playing vibrato:

1. Avoid just rapid movement of the left hand without thinking of the piece you're playing. On a slower piece, use a slow vibrato with tasteful overtones...Play a vibrato where the warbling is kept to a minimum and the vibrato itself is subtle and contributory to the piece I'm playing.
2. Try to move the arm with the wrist and not the wrist alone...the forearm should have a slight movement to it as you're moving the wrist. This would contribute to a stronger more forceful vibrato as opposed to a weaker wrist movement only vibrato. I believe this also adds to the control of the vibrato.
3. I've noticed that it's far easier to have a controlled movement when playing with the 3rd and 4th fingers than the 1st and 2nd fingers. And, the 1st finger is especially hard to emit a solid vibrato from. To overcome a weak 1st and 2nd finger vibrato, try lowering your thumb slightly behind the neck. Instead of the thumb riding high on the edge of the neck, the thumb placed lower and right below the edge of the neck, seems to release the 1st and 2nd fingers to move more freely. Please consult with your instructor on this...I only know this works for me.
4. When practicing vibrato, try playing closed position scales and focus on all four fingers independent of each other to ensure that you have an even feel for vibrato...without the imbalance of one finger having a stronger vibrato feel over another.
5. When performing a vibrato, avoid any type of slide movement of the finger. The tip of the finger should be rolling back and forth slightly...there should never be any slide movement whatsoever.

Definition of Vibrato:

Vibrato: An effect, once an ornament but now a standard part of tone production, whereby a singer or instrumentalist imparts a throbbing quality to a note by oscillating between it and a pitch slightly below. With singers, the louder the note, the more pronounced, usually, the vibrato—and the oscillation can become so wide that the hearer may be left in doubt as to just which note is being aimed for. If the technique is applied, as it often is, to a fairly rapid passage, the result is quite unnerving and totally unmusical (except, apparently, in the opera house).

The LaRousse Encyclopedia of Music,
Hamlyn, 1971
p. 547

Is the vibrato movement going from side to side or up and down?

It's a wrist movement from side to side...Roll the tip of my finger from side to side synchronized with the movement of the wrist....think about it: when moving your fingers up the neck, you're increasing the pitch...when moving down the neck, you're lowering the pitch...hence, by shortening this movement to a rapid side to side (pitches are then going up and down) within a small space of the string, you will get a warble from the pitches moving above and below the note where your finger is placed. Seems to me, if you're going up and down in movement, you wouldn't be noticeably raising or lowering the pitch of the string...and it may take more overall movement to notice the pitch variations that create a vibrato.

Be careful to not overdo this; try a controlled side to side wrist driven movement so that your vibrato is subtle most of the time...otherwise, you may take away from the music you're playing by putting too much emphasis on the vibrato...let the vibrato enhance each individual piece of music you're playing not bring attention to itself. Each song should dictate its own level of vibrato...