Vibrato is an effect that comes from the variation of the target note frequency using an exaggerated pressure on the string with a left hand finger, followed by a pressure release. There are several ways to obtain a vibrato, either with an horizontal oscillation of the finger on the fret, or by a vertical oscillation of the finger on the fret. The speed of this oscillation determines whether a vibraoto is slow or fast. Though each vibrato must be playable with all four fingers, it's more often than not the ring finger that is chosen due to the fact that is can be better controlled.
the palm of the hand stays at an equal distance from the neck. The finger must be pinned at the same place (first example). If the finger moves as is the case on the second example, that creates parasite noises ans the control over the sound is tougher. The third example shows a vibrato played with each finger.
soft vertical Vibrato
the side of the hand rests under the neck and the finger presses and moves the string downwards (or upwards) before the release, several times in a row. This vibrato, when played very quickly without the hand touching the neck, gives the typical Rosenberg sound. The second example shows a vertical vibrato played with each finger.
Strong vertical vibrato
This kind of vibrato is the one that gives his typical sound tp Stochelo Rosenberg, the absolute master of this movement. It is very hard to achieve (I can't do it properly on the following videos) because it demands a lot of strength in the left arm. The palm of the hand must not be in contact with the neck like previously. The movement only stems from the forearm that is really tensed and that must literally shake. You can use another finger to more firmly bend the string. When this vibrato is applied onto the high E string, the string must be bent upwards (which is far from being easy). For the other strings, you can bend the string downwards, or oscillate around the string, alternatively above and under (easier).
|Strong vibrato on the A string|
|Strong vibrato on the high E string|