[sdiy] harmonics & vibrato

[Ian Fritz]

At 02:33 AM 12/18/2002, Scott Evans, Gen Mgr wrote:
Brendan Lynskey wrote:
>>Thinking out loud, (well...in black and white), as the fingertip isn't an
>>infinitesimal point, could it be true that different harmonics are damped to
>>different degrees, depending on how close a part of the finger'pad' is to
>>the peaks/troughs of the harm?

>No, as the strings pitch would be determined by the freely vibrating 
>portion of the string which would be anything not under the finger. Any 
>size finger will do.

As a physicist and onetime cellist, I agree with Brenda.  The finger does 
not give a sharp, hard boundary.  This is why open strings sound *way* 
different from stopped ones.  And mechanical damping generally increases 
with increasing frequency, so higher harmonics should be affected more.


>>And wouldn't this effect change depending on the 'phase' of the
>>vibrato...and so wouldn't the timbre change through each vibrato cycle?
>
>Good question here. Although I have no scientific theory to back this up, 
>I suspect that this matters little, with the "frequency" of the vibrato 
>being so slow in comparison to the pitch. Anyone out there care to comment 
>on this one?

Sorry, but wrong again.  The effect Brenda describes is exactly what 
explains the rich dynamic sound of string instruments, and the whole reason 
for building filter banks to simulate string sounds.  Please read the 
Matthews and Kohut paper refered to here earlier, which describes the 
effect in great detail.  As far as modulation theory, the modulation index 
(m) for vibrato is around 1.  Not insignificant at all.

   Ian