@hemmer Is the Pony VCF also on your list?
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It is, it’s on my workbench. Little hard to know how to approach this one. It’s based on SSI2144 FATKEYS™ Chip, with resonance compensation. Is it acceptable to take (and reference) an appropriately licensed ladder vcf implementation, and just tune the response? Getting the feedback mechanism sounding like the hardware will be the tricky part.
I don’t have the skills to model the circuitry of the chip (or surrounding circuitry).
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No sin to ask around for a pointer or guidance or just get someone to do it for you. It’s for the greater good of more free Befaco!! lol, but seriously ask Vult or Cytomic or other modeling genius, worst could happen is you are rebuffed and no worse off. You other work has been terrific and I love the idea of fully poly Pony VCO, thank you!! Maybe take a crack at the VCF anyway and see what you see. Can’t wait to play around with Burst!! Thanks again
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SurgeXT has the same license as Befaco and I’m sure they wouldn’t mind donating one of the filter models for starting. Maybe have a chat with @baconpaul and see if there’s a fit.
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I have a kit on order for it and will probably have built it by the end of the week. Whatever solution you find, if you want me to A/B anything, then let me know.
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Cheers! I’ve actually had one myself for a little while, just been prioritising midi thing / octaves work. But if/when there’s something up and running getting people with the hardware to check would be super helpful.
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It’ll be interesting to hear how much my calibration is off 
Just want to say thanks for realizing these wonderful hardware modules with pride and conviction. A real joy to use this collection.
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All of our filters are here in a gol3+ header only 4-way simd library:
That also includes tests and a sample juce plugin which run them and of course if you want a rack example of using them the surge xt module does exactly that
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Are any of them models of an SMM 2044?
I’m not sure what that is so probably not!
that’s a typo! I meant SSM 2044 - same chip I used in the Voyetra 8 in the early 80’s! This Befaco is supposed to be a “SSI2144”, so I just assumed that’s a clone that you can still get. But I don’t know…
I figure the virtual version of this Pony VCF is supposed be be an emulation, so…
Well I’m still not sure what that is!
We have models based loosely on research of the moog ladder, the obxd filter, the korg sallen whatzit, a diode ladder, and a couple of super interesting esoteric models from Jatin as well as a collection of svf and other basics. I haven’t actually read any of this thread other than Lars asking if we would share our filters
“Based on Dave Rossum’s patented classic improved ladder topology”
https://www.soundsemiconductor.com/downloads/ssi2144datasheet.pdf
And, quoting from the sheet:
“The SSI2144 reprises the SSM2044 of legacy chipmaker Solid State Micro Technology, which many believe to be the best-sounding analog synthesis filter IC ever produced”
SSM2044 is also used in a bunch of classic synths like Prophet 5 and also Polysix, PPG Wave and others.
SSI2144 is also used in Prophet 5/10 reissue by Sequential.
No, the 2044 was not used in the prophet. That thing used all Curtis chips, no SSM.
Prophet 5 rev. 2 use SSM2040 filter IC’s (excerpt from Prophet 5 Synthesizer Technical Manual TM1000C jan. 1980 p. 2-30):
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Thanks all for the useful input. Taking a step back, in general my philosophy (and one shared by team at Befaco) is that the VCV versions should be faithful representations that reflect the hardware, but not necessarily perfect emulations. They should get the key ideas and character (e.g. with wavefolders, I’m careful to capture the response accurately) but may only approximate other parts. Someone buying the module shouldn’t get any big surprises, but could probably tell them apart (sometimes!).
By example, the recent Wasp filter, which was a very carefully circuit modelled project, represents a higher level of detail/emulation than I (or Befaco) are prepared to invest. For PonyVCF the key parts to capture are
- 4 pole low pass, transistor ladder
- Self oscillating
- Three channel mixer with VCA (and appropriate CV)
- Some sort of feedback for channel 3
- Some gain compensation
I really am looking to take a pre-existing ladder model, tune it, add appropriate CV control. Thanks to all for resources about where to start! I suspect it’s a case of trying a few and seeing which match most closely (though if anyone has intuition about specific models that might be close please say).
The reason I’m asking is also partly, it’s one thing to adhere to the license but it’s also nice if the original authors are supportive, given the usage here is effectively minor tweaks and reskinning.
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We write surge code so people can use it as long as they read the licenses. We even break into submodule some parts have less restrictive licenses ! (By which I mean - even though it looks like it might not help in this instance, thrilled for you to use any of our code in whatever license adhering context you want)
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