[sdiy] Other resonator designs

[Tom Wiltshire]

I'm definitely a fan of resonators, and not just for sweepy, phasey  
filter weirdness. JH has some demos on his site of how well-placed  
filters can make a string sound very much more stringy, and Ken  
Elhardt's polymoog resonator demo shows a similar improvement on some  
basic brass sounds. Most (all?) acoustic instruments include some  
cavity or body that resonates to increase the volume and improve the  
tone. Sounds without this character sound artificial, and that  
(unfortunately) covers a lot of synths. Which is not to say that  
sometimes pure, synthetic, artificial sound isn't what you're after,  
but I like the idea of having a virtual instrument body to tweak  
along with other sound parameters.

With this in mind, all this discussion of resonators set me looking  
at various schematics for them again.

There's the PolyKorg version, very simple and based on vactrols, but  
bandpass response only, and no resonance control:

	http://homepage2.nifty.com/rjb/pdf/ 
rjb_diy_synthe_701a_resonator_schem_revA.pdf

or alternatively:

	http://www.modular.fonik.de/pdf/PS3100.pdf

Then there's state variable filter based designs, which have all the  
options, but are quite a bit more complicated, like this one, based  
on the MFOS SVF.

	http://mypeoplepc.com/members/scottnoanh/birthofasynth/id25.html

I've done a similar SVF resonator stage myself, based on Roman Sowa's  
Dual SVF design (although I haven't got the LPF and HPF outputs on  
this schematic):

	http://www.electricdruid.com/VCResonator.jpg

(basically just the filter from http://sowa.synth.net/modular/vcf.html)

The Polymoog SVF design that Florian posted earlier, good but not  
voltage controlled like the ones above:

	http://fa.utfs.org/diy/polymoog/polymoog_resonator_schematics.jpg

Enjoy!
T.