When string players use vibrato, the movement of their hands looks as if they are changing the point at which the string is stopped against the fingerboard. This should change the pitch of the note. But what I hear is not a pitch change but a change in volume. Am I misunderstanding what is going on?
鈥� Your correspondent is mishearing vibrato on stringed instruments. Classical vibrato, as used by violinists, involves rocking the finger back and forth parallel to the string. This alternately lengthens and shortens the vibrating string, producing a variation in pitch. I suspect that rapid vibrato, especially, can give the impression of greater volume. The bow can also be driven harder at the same time, which will produce an actual volume increase.
Guitarists also use classical vibrato. On the guitar, this has the effect of increasing and then lowering string tension, producing a change in pitch. Sideways vibrato, as used in blues and rock playing, also stretches and unstretches the string, with a corresponding pitch variation. However, guitars have frets, unlike a violin, so vibrato cannot lower the pitch below that of the fretted note, whereas a violinist can move above and below the initial pitch.
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Blues and rock players can get a true 鈥渦p and down鈥� pitch vibrato only when they have initially bent the string sideways to give a new note. A sideways vibrato then gives notes both above and below this pitch.
In theory, you can impart more energy to the string with vibrato, but on the violin this is negligible in comparison with the energy from bowing. On the guitar, vibrato has a dampening effect, causing the note to decay faster.
Neil Paterson, Wormit, Fife, UK