But of course. If you’re an arm-vibrato-er, I guess that could account for your viewpoint.
Eh?
I worked damn hard to get the flexibility and strength in my hand for wrist vibrato that I could vary and control - and just now I had to stop myself using half of it!
I can get a one-way vibrato easy enough with a guitar just by bending a string up and down (perpendicular to the length of the string).
However, with wrist vibrato (where the finger is rocked back and forth parallel with the length of the string, though the tip barely moves), I have a hard time not oscillating up and down in pitch above and below the fretted note.
Looks like the issue of the nature of vibrato (variations in pitch for the purposes of this discussion) is neither as simple nor as predictable as I had hoped.
It may be unilateral or bilateral, apparently. Someone proposed experimentation to help determine this, and while that was one step in development I had hoped to avoid by doing this kind of research, it looks like it will indeed be necessary.
I have to say this: I expected some replies, but I sure didn’t expect this level of interest and participation on such a subject as this! Thanks again.
Good point. This is the standard rock vibrato technique, and since it is produced by bending the string, it is only possible for the oscillation to go above the “true” pitch. The other technique you mention is a more subtle effect: it does both raise and lower the pitch, but only by a rather small amount.
I’ve spent a bit of time slowing down samples, and here’s my ever-so-scientific results:
Violinists (Kreisler, Menuhin, Heifitz), and Janis Joplin: All go above and below.
Maria Callas, Elvis and Sinatra - both go below, and also slightly above.
Pablo Casals - below only. Jpeg Jones may have a point there.
I wonder if ‘below only’ is an American thing?
I randomly stumlbed across this piece of Linux software, which may be useful: http://pitchtune.sourceforge.net/
Geographical differences are certainly plausible - but ‘American-only’ wouldn’t explain Casals.
Further listening (damn, i had to listen to 3 hours of Wagner, such a shame 
)… opera singers definitly go ‘below’, but the timbral change of the more open mouth and throat is easily as significant as any pitch change.