GIC String Filter - first experiments (was: [sdiy] Filter Banks & CSound)

[Ian Fritz]

Hi Juergen --

>I've finally made my own version of a String Filter Bank.
>Samples from some first experiments are avaiable at
>http://home.debitel.net/user/jhaible/jh_string_filter.html

Congratulations!  That's a big project.  I think I have some idea of what 
it means to "select" the caps.  :-)

The demos sound great, although I don't hear the highest freqs any more.

Did you use the usual Burhans frequency ratio?  What is the maximum 
peak-to-valley ratio on the second demo?  It sounds like you are getting up 
to about the 8-10 range.

>I think the peak/valley ratio of the main filter bank is ok,
>but the air/wood/bridge resonance needs some more
>adjustments. Any hints how to improove this are welcome.
>(Benade gives detailed information about the frequency -
>125Hz, 175Hz, 1.5kHz and 2kHz for Cello -, but not
>about Q and Gain.)

There have been many measurements of violin resonances.  A fairly detailed 
summary can be found in the Fletcher and Rossing book (The Physics of 
Musical Instruments).  Concerning violas and cellos they say "...one must 
search diligently to find 1 or 2% as much published material on their 
acoustical behavior."

For cello, they list the lowest modes as 57, 102, 144, 170, 195, 203, 219, 
277, 302 (Hz).  The lowest mode is the C1 bending mode and is probably 
quite weak.  102 Hz is the A0 (air) mode and 144 Hz is the T1 mode.  The C3 
and C4 modes are at 219 and 195.  They don't actually show any admittance 
curves for cello, unfortunately.  For violin, the A0, T1, C3 and C4 modes 
are the strongest low-frequency resonances, and look quite a bit stronger 
than the higher frequency modes.  So you might try frequencies of 102, 144 
and ~200+.  Also, violin has an overall -9 db/Oct output above about 700 
Hz, so you might want to try prefiltering the input sawtooth a bit.  Also, 
experiment with a pulse drive with different widths.

Please keep us posted on this very interesting work!

   Ian