Creating a pulse
As we talked about in Concept of vibrato, we need to create a pulse in our vibrato. When we vibrate we bend the pitch slightly higher and lower. In other words, there will be a low and high points in pitch when we vibrate. These points become the pulse when you vibrate.
You can make either the high or the low point of the pitch as the point of the pulse. I recommend the high point to make the pulse because you are aiming towards the higher region of the pitch this way, which will make your tone brighter than when you are aiming towards the lower region of the pitch. In this article, I will explain assuming that we are going for the high point.
Either way, do not aim for both the high and the low points to make 'two' pulses in each cycle of a vibrato. You go for either the high or the low point.
Practice with a metronome
We need a bow for these exercises.
We set a metronome at 50, and match the high point of the pitch to the metronome. When the metronome clicks you are at the high point of the pitch. Move quickly to the top of the pitch and relax as soon as you get to the top. In other words, the vibrato motion is not made at an even speed. Going upward is very quick and comes back slowly. This will create a pulse at the top of the pitch.
When you can comfortably match the top of the pitch with the metronome, create 2 pulses in 1 click of the metronome. When you can do that, create 3 pulses in 1 click, then 4 pulses, then 6 pulses in 1 click.
When you can create 6 pulses in 1 click of a metronome, that is already a real vibrato. Most of us will find that we cannot control our vibrato motion perfectly at one point or another before we can get to the 6 pulses in 1 click. And that's where you really have to practice. Don't move onto a faster vibrato motion when you can not control the motion perfectly at a lower frequency of the pulse.
Gain total control of your vibrato
When you practice the way I just explained, you will start to notice that you are able to control the speed and width of the vibrato. Vibrato is not a random hand trembling motion; It is an intelligent and informed decision of a technical application that will enhance the beauty of the music you are playing. Some music would require a fast vibrato, while some other music may require a wide vibrato. We need to think about the types of vibrato in each phrase, and be able to execute the type of vibrato that is appropriate for the occasion.
Once you can play 6 pulses in one click, you can practice with different speed and width of vibrato. You can combine fast and wide, slow and wide, fast and narrow, and so on. After a while you will gain a total control of your vibrato, and you will be able to produce all kinds of tone colors and atmosphere from changing the types of vibrato.
Add a vibrato practice to your daily routine. You just have to put in 5 to 10 minutes everyday for vibrato. Continue the routine for a few months, and you will see a dramatic difference in your vibrato!