One thing that differentiates us jazz violinists from our classical brothers and sisters, is the use of vibrato. Often people think that there should be no vibrato on violin in jazz, but this seems to me to have no basis. Listen to any great sax player, even John Coltrane, and you will hear a range of vibratoes. Trumpet players, trombonists, even some guitarists, use vibrato. Listen to singers like Johnny Hartman, or Billy Eckstine. Only pianists and drummers don't use vibrato (and I have even seen film of Keith Jarrett wobbling his fingers on the keyboard – he wishes he could).
No, there is certainly room for vibrato in jazz on violin, but we have to use it consciously, and with care. Most other frontline instruments don't play with that continuous through-vibrato such as most classical violinists use, but introduce it gradually towards the ends of the notes. Equally, it is not of a constant speed, or width, but varies, according to need and taste.
There are two main types of vibrato: one that varies pitch, and another that gives a kind of throb in intensity. To start, I am going to deal with the pitch-wobbling type.
In this vibrato, the finger tip, or pad (depending on your finger angle) rolls one way then the other. If we roll up to the note from below, we get a feeling of sliding into the note. If you hit the note spot on, then you roll below the note, and back up. The vibrato should not move above the intended pitch, because we hear the top of the wobble as the pitch of the tone. If you go above the note, we hear the note as being sharp.
In general, the lower the position on the fiddle, the wider, physically, you can have your vibrato.
As you get into the higher positions, you need a narrower wobble width, so you don't span two chromatic notes. The vibrato pitch range should be somewhat less than a semitone, so you have to take care of how much your finger is rolling back and forth.
The speed of the vibrato can be lower for lower notes, as well. Higher notes can take a faster vibrato, but even so, we can use a slow vibrato on high notes, if it is very narrow. Sometimes, to my ear, a slow narrow vibrato sounds like I am “chewing” the note. A fast vibrato on lower notes can sound a bit manic, especially if it is quite wide.
We can start slow and narrow, and speed up, or widen the vibrato, as we wish. A note with vibrato will contrast with a plain note, so you can choose which notes to draw attention to by giving them some vibrato colour.
There is another kind of wobbling vibrato that actually slides the finger a little bit down and up. I call this the “blues” vibrato. It has quite a different feel from the rolling finger vibrato, but still shifts the note's pitch. Violinists who use this a great deal are Billy Bang and Regina Carter, as did Stuff Smith. It has a wild sound, a wide wail that gives the note some considerable intensity. However, because it enriches the note so much I suggest that the blues vibrato should be used with caution.
Now we come to what Steven Redrobe calls the “impulse” vibrato, so called because rather than wobbling the note in pitch, you get a variation in its volume or intensity, like a series of impulses going into the string, which give the note a throbbing effect. This is achieved mainly by squeezing and relaxing the left hand, so that the pressure if the fingers on the string increases and reduces. I think this changes the density of the finger tip, and so changes the way that the string is damped by the finger. It gives a glorious liveliness to the sound, and its speed is very controllable. You do get a little pitch wobble, but that is a by-product rather than the aim of the approach.
To sum up, I have described three types of vibrato, all of which we can use on our violins to make our jazz sound more interesting and personal. We can introduce it as and when we will, to help shape our lines, and get the most out of our sound.