[sdiy] harmonics & vibrato

[Scott Evans, Gen Mgr]

Thanks Ian,

I stand corrected. Of course the open strings sound different as the end 
of the string is supported at the bridge rather than the finger. But I 
don't think my reponse is way off the mark here. I think that these 
changes have more to do with the strength (Amplitude) of the harmonics 
and not so much the phase relationship thereof, hence the use of a 
filter bank, which alters harmonic strength, would be a good model. Any 
phase changes in the filter bank would be peculiar to the electronic 
circuits and not so much a model in recreating any such changes in the 
violin. But, I will defer until I have reviewed these articles and I 
appreciate your response and help in this direction.

What is really fun to think about is the effect of bowing the string and 
the implications of the changes this makes in regards to these phase and 
amplitude relationships.

Regards, Scott
-------------------------------------------------------------
Ian Fritz wrote:
> 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
> 
> 
>