Vibrato is the word used to describe the vibrations of the left hand on a stringed instrument, which creates a slight undulation in the pitch of the note and produces a richer more luscious sound. In David's film on the natural resonances of the strings and the instrument's sympathetic vibrations, he used no vibrato at all, simply focusing on holding down the strings effectively as possible, so that the sympathetic vibrations could be maximised.
One form of vibrato which was enjoyed in the early part of the 19th Century was described by Dotzauer (a famous cellist and pedagogue of the time) and was called Pochens. This sound is achieved by playing with the sympathetic vibrating strings, stopping them and then releasing them again, to create a sound that is very close to what we do nowadays as vibrato. Modern vibrato is normally described as the variety of pitch as the left hand moves up and down the string, but you can also hear the throbbing of the sympathetic notes even though you can't see it.
Vibrato can be varied in speed and in width, and these variable factors can be used in different ways to express different emotions they can be nervy or sad - the sky is the limit.
Different music calls for different vibrato so when David performs unaccompanied Bach, the main concern is to generate as much sympathetic resonance from the instrument as possible, rather than simply using vibrato as a melodic device.
If he is playing a more romantic tune, the vibrato will be a much bigger part of his melodic element. In the film above David plays a theme from the Concerto for Cello and Orchestra by Dvorak.
You can hear how he varies the vibrato, for instance on the note that joins the two phrases (The E natural in the penultimate bar) his vibrato slows down as it's the last note of the phrase and then it speeds up again, as he joins those two phrases together.
So the vibrato is never the same for each note as musicians always vary the intensity (as a singer would), to guide the ear through the phrase.
It's commonly assumed that vibrato was used increasingly during the 19th Century, so during the middle of the 18th Century, with Bach one shouldn't use vibrato, then more with Mozart, during the 19th Century more and more, then Tchaikovsky and Dvorak vibrato would be the norm. In fact, if you read what musicians and composers were writing about how they expected their music to be played, then vibrato really played the same role during the 19th Century and didn't change until the 1920's. Before this watershed performers and composers felt that vibrato was simply another of the ornaments that were available to performers as part of their expression. So vibrato might be added 3 or 4 times per page on particular notes and for particular expressive effects.
After the 1st World War, the violinists Kriesler and Heifetz (amongst others) started to use a beguiling, sweet, constantly vibrated sound. One theory is that because of the huge number of gramophone records that they made (and don't forget, these were the first ever recordings), their sound became the norm for sting playing. Certainly Heifetz's teacher – Leopold Auer writing in 1921 was very quick to say that his way of considering vibrato lined up with the Paris Conservatoire, where it was one of the ornaments like a trill or a mordant – the vibrated note. He felt that it was an expressive ornament that was part of his quiver of arrows that he could expressively add to the music. However, Auer wrote, 'some of my pupils disagree with me and they want vibrato to be part of the continuous sound.'
Now of course – in the 21st century, the musical world is divided between those who agree with Heifetz and some agree with his teacher, Leopold Auer. We have those who want to make vibrato part of their constant sound production and others who want to use it as an expressive ornament and to be occasionally added as part of a phrase.
For most string players, vibrato will come almost subconsciously, from their emotional response to the music that they see in front of them. With contemporary music this can sometimes be a problem because it is not always apparent exactly what the composer wants in terms of mood. This can be helped by indicating whether vibrato is an important part of the music or not. Senza vibrato (no vibrato) or Molto vibrato are useful markings to add to the music, as unless a marking is made, players will apply their own ideas about vibrato to the music. One thing to remember is that for all string players, the way that the vibrato is linked to the expression of the bow is so deeply engrained, that if you ask a string player to speed up and intensify their vibrato, whilst doing a diminuendo with the bow, because of the way that humans work, that will probably be very difficult for them to do.
The technique of vibrato is often challenging for a beginner to pick up, but David offers some ideas…. 'Firstly, I'm trying to keep my arm as relaxed as possible whilst embed my finger into the fingerboard. Having a completely relaxed left arm allows me to speed up the vibrato as much as I like. With the violin the technique is different. For us, it's using the whole forearm, so with a relaxed upper arm and a rolling forearm, or I can add an element of wrist, or I can even allow the joint of the finger to move in and out to help the pitch changes smoothly. Sometimes it's helpful to support my second finger with a little help from my third finger, this just helps to get it embedded into the fingerboard.'
You can also add vibrato to open strings! The sympathetic resonance when you play a stopped note, (for example a G), and allow the open string also rings works the other way, so you can play the open G and have the stopped G ring. If you then add vibrato to the stopped note that gives the effect of doing vibrato on an open string.